The Vaccine Discovery Process: History and Milestones

Introduction
What is the Vaccine Discovery Process?
The Ancient Roots of Immunization
3.1. Variolation in China and India
3.2. Ottoman Practices and European Introduction
Edward Jenner and the Birth of Vaccination
4.1. The Cowpox Experiment
4.2. Scientific Opposition and Societal Resistance
4.3. Global Impact and Smallpox Eradication
Louis Pasteur’s Laboratory Revolution
5.1. Germ Theory and Attenuation
5.2. Anthrax Vaccine Development
5.3. Rabies Vaccine Breakthrough
5.4. Ethical Considerations
Toxoid Vaccines for Bacterial Diseases
6.1. Diphtheria: From Antitoxin to Vaccine
6.2. Tetanus Toxoid Development
6.3. Manufacturing Challenges
The Polio Vaccine Campaign
7.1. Jonas Salk and the Killed-Virus Approach
7.2. The Polio Pioneer Trials
7.3. Albert Sabin’s Oral Vaccine
7.4. Global Eradication Efforts
Influenza: The Annual Challenge
8.1. Discovery and Early Vaccines
8.2. Antigenic Drift and Shift
8.3. Annual Reformulation Process
8.4. Production Challenges
Childhood Combination Vaccines
9.1. Measles Vaccine Development
9.2. Mumps and Rubella Vaccines
9.3. The MMR Combination
9.4. Global Implementation
Bacterial Capsule Vaccines
10.1. Pneumococcal Vaccine Challenges
10.2. Hib Conjugate Technology
10.3. Production Innovation
Recombinant Vaccine Technology
11.1. Hepatitis B Breakthrough
11.2. Hepatitis A Development
11.3. Biotechnology Revolution
COVID-19 and the mRNA Revolution
12.1. Decades of mRNA Research
12.2. Katalin Karikó and Drew Weissman
12.3. Rapid Development and Deployment
12.4. Global Distribution Challenges
Scientists Behind the Vaccine Discovery Process
13.1. Edward Jenner
13.2. Louis Pasteur
13.3. Emil von Behring
13.4. Maurice Hilleman
13.5. Baruch Blumberg
13.6. Jonas Salk and Albert Sabin
13.7. Katalin Karikó and Drew Weissman
Clinical Trial Protocols
14.1. Early Experimental Approaches
14.2. Randomized Controlled Trials
14.3. Modern Fast-Track Protocols
Vaccine Opposition Throughout History
15.1. Religious and Philosophical Opposition
15.2. 19th Century Anti-Vaccination Movements
15.3. Modern Vaccine Hesitancy
15.4. Social Media Impact
Technology and Social Change
16.1. Genomic Surveillance
16.2. Artificial Intelligence
16.3. Digital Communication
Barriers in the Vaccine Discovery Process
17.1. Scientific Uncertainties
17.2. Pathogen Variability
17.3. Manufacturing and Distribution
17.4. Ethical and Social Challenges
17.5. Global Access and Equity
The Future of the Vaccine Discovery Process
18.1. Universal Vaccines
18.2. Personalized Immunization
18.3. Next-Generation Platforms
Conclusion
Sources

1. Introduction

The vaccine discovery process represents one of humanity’s most transformative scientific achievements. Throughout history, infectious diseases claimed countless lives, decimated populations, and shaped civilizations. Consequently, the development of vaccines fundamentally changed this reality, offering protection against deadly pathogens and saving millions of lives each year. Indeed, the vaccine discovery process encompasses not merely laboratory science but also clinical experimentation, public health strategy, ethical debate, and social acceptance (WHO).

Understanding the vaccine discovery process requires examining centuries of scientific progress—from ancient variolation practices to modern genetic engineering. Furthermore, each vaccine tells a unique story of curiosity, persistence, and courage. Scientists faced skepticism, technical failures, ethical dilemmas, and sometimes public hostility. Nevertheless, through rigorous experimentation and global collaboration, the vaccine discovery process evolved into a sophisticated, multidisciplinary endeavor that continues to protect humanity from emerging threats (Frontiers).

2. What is the Vaccine Discovery Process?

The vaccine discovery process begins with identifying a disease-causing pathogen and understanding its interaction with the human immune system. Specifically, vaccines introduce antigens—fragments or weakened forms of pathogens—that train the immune system to recognize and combat future infections. Consequently, this process involves multiple stages: pathogen isolation, antigen selection, laboratory testing, animal studies, clinical trials in humans, regulatory approval, manufacturing scale-up, and post-market surveillance.

Flowchart showing every stage of the vaccine discovery process, from detecting the pathogen to global immunization

Different vaccine types emerged throughout the vaccine discovery process history. For instance, live attenuated vaccines use weakened pathogens, whereas inactivated vaccines contain killed organisms. Similarly, subunit vaccines include specific protein fragments, toxoid vaccines neutralize bacterial toxins, conjugate vaccines link polysaccharides to proteins, and genetic vaccines (mRNA/DNA) instruct cells to produce antigens. Importantly, each approach reflects scientific understanding at different historical moments, with innovations building upon previous discoveries.

The vaccine discovery process demands collaboration across disciplines: microbiology, immunology, chemistry, epidemiology, manufacturing, public health, and communications. Moreover, success requires not only scientific breakthroughs but also public trust, regulatory frameworks, manufacturing capacity, and equitable distribution systems (Frontiers).

3. The Ancient Roots of Immunization

Long before the modern vaccine discovery process emerged, ancient societies observed that surviving certain diseases conferred immunity. Consequently, this empirical understanding led to deliberate exposure practices known as variolation, marking humanity’s first attempts at controlled immunization.

3.1. Variolation in China and India

In 16th-century China, physicians developed variolation against smallpox by collecting material from pustules of mild cases. Subsequently, they dried this material, ground it into powder, and introduced it into healthy individuals through nasal insufflation. Furthermore, historical texts describe this practice spreading through Chinese provinces, particularly among wealthy families seeking to protect children during epidemics.

Similarly, Indian practitioners employed cutaneous variolation, scratching smallpox matter into the skin. Despite being risky, these methods demonstrated empirical effectiveness. Notably, observers noted that individuals who underwent variolation typically experienced milder disease and survived at higher rates than those naturally infected. Thus, this represented the earliest phase of the vaccine discovery process, built entirely on observation rather than scientific understanding (WHO).

3.2. Ottoman Practices and European Introduction

Meanwhile, Ottoman physicians refined variolation techniques, which came to European attention through Lady Mary Wortley Montagu in 1721. After observing successful inoculations in Constantinople, she had her own children variolated and advocated for the practice in England. Specifically, the method involved inserting threads soaked in pustule material under the skin.

Benjamin Franklin, initially skeptical, became a strong advocate after his son died from smallpox. Consequently, he publicly promoted variolation despite religious opposition and concerns about unnatural interference with divine will. Furthermore, Colonial American physicians conducted variolation campaigns during epidemics, though controversy persisted. Importantly, death rates from variolation ranged from 1-2%, significantly lower than natural smallpox mortality of 20-30%, yet public fear remained substantial (WHO).

4. Edward Jenner and the Birth of Vaccination

Edward Jenner transformed the vaccine discovery process by applying scientific method to folk observations, creating modern vaccinology’s foundation.

4.1. The Cowpox Experiment

In rural Gloucestershire, Edward Jenner heard milkmaids claim that cowpox infection protected them from smallpox. For years, Jenner pondered this relationship. Although Benjamin Jesty had performed similar experiments in 1774, Jenner’s systematic approach and documentation proved decisive.

On May 14, 1796, Jenner collected material from cowpox lesions on milkmaid Sarah Nelms’ hands and inoculated eight-year-old James Phipps, son of his gardener. Initially, Phipps developed mild fever and discomfort but recovered completely. Subsequently, six weeks later, Jenner exposed Phipps to fresh smallpox matter multiple times. Remarkably, the boy never developed smallpox, demonstrating acquired immunity through cowpox exposure (PMC).

4.2. Scientific Opposition and Societal Resistance

Jenner submitted his findings to the Royal Society in 1797, but the paper was rejected for insufficient evidence. However, undeterred, he conducted additional experiments on 23 subjects, documenting each case meticulously. Subsequently, in 1798, he privately published “An Inquiry into the Causes and Effects of the Variolae Vaccinae,” introducing the term “vaccination” from the Latin vacca (cow).

Initially, medical professionals resisted Jenner’s method. Additionally, variolators whose incomes depended on the old practice campaigned against him. Furthermore, religious leaders preached that vaccination interfered with God’s plan. Moreover, contamination issues arose when cowpox samples were handled improperly, sometimes resulting in accidental smallpox transmission. Consequently, these early challenges in the vaccine discovery process demonstrated that scientific innovation requires more than laboratory success—it demands public education, quality control, and persistence against opposition (Jenner Institute).

4.3. Global Impact and Smallpox Eradication

Despite resistance, vaccination’s superiority became undeniable. For instance, the British military adopted vaccination; Napoleon vaccinated his army. Subsequently, by the mid-1800s, most European nations implemented vaccination programs. Ultimately, the vaccine discovery process that Jenner initiated led to the World Health Organization’s global eradication campaign, which declared smallpox extinct in 1980—the only human disease ever eradicated. Indeed, this monumental achievement validated Jenner’s vision and demonstrated what the vaccine discovery process could accomplish with sustained global effort (WHO).

5. Louis Pasteur’s Laboratory Revolution

Louis Pasteur revolutionized the vaccine discovery process by introducing controlled laboratory experimentation and germ theory principles, transforming vaccination from empirical practice into predictive science.

5.1. Germ Theory and Attenuation

Pasteur’s investigations into fermentation and disease causation established that specific microorganisms caused specific diseases. Consequently, this understanding enabled intentional manipulation of pathogens. Furthermore, through serial passage and controlled aging, Pasteur discovered attenuation—weakening microorganisms while preserving their immunogenic properties. As a result, this breakthrough fundamentally altered the vaccine discovery process, making it reproducible and designable rather than dependent on natural occurrence like cowpox (Frontiers).

5.2. Anthrax Vaccine Development

In 1881, Pasteur developed an anthrax vaccine by exposing anthrax bacteria to oxygen at specific temperatures, reducing virulence. Furthermore, he staged a dramatic public demonstration at Pouilly-le-Fort, vaccinating 24 sheep, one goat, and six cows while leaving controls unvaccinated. Subsequently, all animals were then challenged with virulent anthrax. Remarkably, the vaccinated animals survived; unvaccinated animals died. Consequently, this spectacular vindication of the vaccine discovery process established Pasteur’s reputation and proved vaccines could be manufactured deliberately (Pasteur Institute).

5.3. Rabies Vaccine Breakthrough

Rabies presented unique challenges. The virus remained invisible under contemporary microscopes, however Pasteur deduced it infected nervous tissue. Through inoculating rabbits with rabid dog brains and serially passaging the virus, he created a “fixed” virus with stable, predictable incubation. Subsequently, he then attenuated this virus by drying infected rabbit spinal cords.

On July 6, 1885, nine-year-old Joseph Meister arrived at Pasteur’s laboratory severely bitten by a rabid dog. At that time, Pasteur had never tested his vaccine on humans. After consultations with physicians Alfred Vulpian and Jacques-Joseph Grancher, they administered 13 injections over 10 days, using progressively stronger viral preparations. Fortunately, Meister survived, and the vaccine discovery process achieved its first human success against a viral disease (PMC).

5.4. Ethical Considerations

Pasteur’s rabies experiment raised profound ethical questions that continue to shape the vaccine discovery process. Indeed, he had no certainty the vaccine would work; failure meant the boy’s death would be attributed to Pasteur’s intervention. Nevertheless, rabies was universally fatal, and desperate parents sought any hope. Consequently, this tension between experimental uncertainty and humanitarian duty established precedents for emergency compassionate use, informed consent, and researcher responsibility that govern modern vaccine trials (EBSCO).

6. Toxoid Vaccines for Bacterial Diseases

The vaccine discovery process advanced significantly when scientists learned to target bacterial toxins rather than the bacteria themselves, creating an entirely new vaccine category.

6.1. Diphtheria: From Antitoxin to Vaccine

Diphtheria, caused by Corynebacterium diphtheriae, killed thousands of children annually. In 1890, Emil von Behring and Shibasaburo Kitasato discovered that injecting diphtheria toxin into animals produced “antitoxins” (antibodies) that could neutralize the toxin. Subsequently, Behring received the first Nobel Prize in Physiology or Medicine in 1901 for this discovery, though Kitasato was controversially excluded.

Initially, early antitoxin therapy reduced mortality dramatically but provided only temporary passive immunity. Therefore, the vaccine discovery process required creating active immunity. Consequently, Behring developed diphtheria AT (antitoxin-toxin) vaccine in 1913, mixing toxin with antitoxin to create complexes that stimulated immunity without causing disease. Importantly, clinical trials in Berlin showed that vaccinated children remained healthy during outbreaks while unvaccinated children succumbed to infection (PMC).

Moreover, Anna Wessels Williams, working at the New York City Health Department, isolated the “Park-Williams No. 8” strain in 1894, which became the standard for antitoxin production worldwide. Furthermore, her contributions to the vaccine discovery process demonstrated the critical role of strain selection in vaccine manufacturing. Although Williams faced discrimination as a woman scientist, she persisted, eventually receiving recognition for her work that saved countless lives (WHO).

6.2. Tetanus Toxoid Development

Tetanus, caused by Clostridium tetani spores in contaminated wounds, produced a powerful neurotoxin causing muscle spasms and often death. Similarly, Emil von Behring and Kitasato also developed tetanus antitoxin in 1890, establishing passive immunization. However, active immunization required a safe vaccine.

Alexander Glenny at the Wellcome Research Laboratories discovered in 1924 that treating tetanus toxin with formaldehyde created “toxoid”—a non-toxic molecule retaining immunogenicity. Consequently, this innovation in the vaccine discovery process allowed safe, effective vaccination. In addition, Glenny also discovered that adding aluminum salts enhanced immune response, inventing the first vaccine adjuvant. Therefore, his work revolutionized vaccine formulation (Proclinical).

6.3. Manufacturing Challenges

Producing consistent, safe toxoid vaccines required industrial-scale microbiology. Specifically, manufacturers grew massive cultures of diphtheria or tetanus bacteria, extracted toxins, treated them with formaldehyde under precise conditions, and tested potency on guinea pigs. Unfortunately, quality control failures occasionally resulted in contaminated batches. For instance, the 1942 Bundaberg disaster in Australia, where poor aseptic technique caused 12 children’s deaths, highlighted manufacturing risks in the vaccine discovery process and led to stricter regulatory oversight (Frontiers).

7. The Polio Vaccine Campaign

Polio epitomizes the 20th-century vaccine discovery process: massive public investment, scientific competition, large-scale clinical trials, and eventual global coordination toward disease elimination.

7.1. Jonas Salk and the Killed-Virus Approach

Poliomyelitis terrorized parents throughout the early 20th century, causing paralysis primarily in children. Moreover, three viral serotypes complicated vaccine development. However, by the 1940s, John Enders, Thomas Weller, and Frederick Robbins succeeded in growing poliovirus in non-neural tissue culture—a breakthrough that earned them the 1954 Nobel Prize and made vaccine development feasible.

Jonas Salk at the University of Pittsburgh chose to develop an inactivated (killed) vaccine using formaldehyde-treated virus. Notably, his approach contradicted conventional wisdom that only live vaccines provided durable immunity. Nevertheless, Salk worked tirelessly, testing different viral strains, inactivation protocols, and dosing schedules. Furthermore, his meticulous attention to safety reflected lessons from earlier vaccine disasters. Overall, the vaccine discovery process he followed emphasized careful validation at each step (Salk Institute).

7.2. The Polio Pioneer Trials

In 1954, the National Foundation for Infantile Paralysis (March of Dimes) organized the largest medical field trial in history. Specifically, over 1.8 million children participated across the United States, including 600,000 who received vaccine, 600,000 who received placebo, and 600,000 observed controls. Furthermore, Dr. Thomas Francis Jr. directed the double-blind study to ensure scientific rigor.

On April 12, 1955—tenth anniversary of President Franklin D. Roosevelt’s death from polio complications—Francis announced results: the vaccine was 80-90% effective against paralytic polio. Immediately, church bells rang nationwide; parents wept with relief. Consequently, Jonas Salk became an instant hero. Indeed, the vaccine discovery process demonstrated that rigorous, large-scale clinical trials could definitively prove vaccine safety and efficacy, setting standards for all future vaccine development (History of Vaccines).

7.3. Albert Sabin’s Oral Vaccine

In contrast, Albert Sabin pursued an alternative approach: live attenuated vaccine administered orally. Through passaging poliovirus through monkey tissue cultures, Sabin selected mutant strains that replicated poorly in human neurons but induced strong intestinal immunity. Importantly, his vaccine prevented viral shedding, reducing community transmission—a significant advantage over Salk’s injectable vaccine.

Initially, Sabin faced challenges conducting human trials in the United States after Salk’s success. Therefore, he partnered with Soviet scientists, conducting massive trials involving 10 million Soviet children in 1959-1960. Fortunately, results confirmed safety and efficacy. Moreover, the oral vaccine’s ease of administration—no needles required—made it ideal for mass campaigns in developing nations. Consequently, by the 1960s, most countries adopted Sabin’s vaccine. Thus, this pragmatic approach in the vaccine discovery process prioritized global accessibility alongside scientific innovation (Science History Institute).

7.4. Global Eradication Efforts

In 1988, the World Health Organization launched the Global Polio Eradication Initiative. Subsequently, through coordinated vaccination campaigns, surveillance, and rapid outbreak response, wild poliovirus was eliminated from most regions. However, by 2025, only Afghanistan and Pakistan report endemic cases. Importantly, the vaccine discovery process extends beyond laboratory development to implementation science, requiring political commitment, community engagement, and logistical excellence. Indeed, polio eradication demonstrates both the promise and complexity of applying the vaccine discovery process to global health challenges (Polio Eradication Initiative).

8. Influenza: The Annual Challenge

Influenza presents unique obstacles in the vaccine discovery process due to constant viral evolution, requiring perpetual adaptation of vaccine formulations.

8.1. Discovery and Early Vaccines

In 1933, British scientists Wilson Smith, Christopher Andrewes, and Patrick Laidlaw isolated the influenza virus by infecting ferrets with throat washings from infected humans. Subsequently, this breakthrough enabled vaccine development. Later, during World War II, Thomas Francis Jr. and Jonas Salk developed the first killed-virus influenza vaccine for military use, protecting troops from anticipated flu epidemics.

Initially, early flu vaccines used chicken eggs to grow virus—a method still used today. Specifically, manufacturers inject virus into fertilized eggs, harvest viral particles, inactivate them, purify antigens, and formulate vaccines. However, this labor-intensive process requires months of production time, constraining the vaccine discovery process for rapidly evolving pathogens (PMC).

8.2. Antigenic Drift and Shift

Influenza’s surface proteins—hemagglutinin (H) and neuraminidase (N)—constantly mutate through “antigenic drift,” causing gradual changes that reduce vaccine effectiveness. Occasionally, reassortment between different strains causes “antigenic shift,” creating pandemic viruses like 1918 H1N1, 1957 H2N2, 1968 H3N2, and 2009 H1N1.

Maurice Hilleman first described antigenic shift in 1957. Working at Walter Reed Army Medical Center, he identified the “Asian flu” pandemic virus, rapidly developed a vaccine, and likely prevented millions of American deaths. His vigilance exemplified how the vaccine discovery process must incorporate ongoing surveillance and rapid response capabilities (Britannica).

8.3. Annual Reformulation Process

Each year, the Global Influenza Surveillance and Response System monitors circulating strains worldwide. In February and September, WHO convenes expert meetings to recommend Northern and Southern Hemisphere vaccine compositions. Manufacturers receive viral seed strains and begin production immediately. This six-month timeline limits adaptability when unexpected variants emerge.

The vaccine discovery process for seasonal influenza requires international data sharing, computational modeling of viral evolution, and manufacturing flexibility. Despite sophisticated surveillance, vaccine-strain mismatches occur when viruses evolve rapidly or unanticipated strains dominate. The 2014-2015 season saw only 19% effectiveness due to H3N2 mismatch, eroding public confidence (Journal of Infectious Diseases).

8.4. Production Challenges

Egg-based production faces limitations: some viruses grow poorly in eggs, mutations arise during egg adaptation, and egg supply constrains capacity. Cell culture and recombinant protein technologies offer alternatives but require new regulatory pathways and manufacturing infrastructure. The vaccine discovery process for influenza continues evolving, with universal flu vaccine candidates targeting conserved viral regions currently in clinical trials (PMC).

9. Childhood Combination Vaccines

The development of measles, mumps, and rubella vaccines represents a pivotal chapter in the vaccine discovery process, transforming childhood disease prevention through combination immunization strategies.

9.1. Measles Vaccine Development

Measles killed approximately 2.6 million people annually before vaccination. In 1954, John Enders and Thomas Peebles isolated measles virus from David Edmonston, a sick Boston student. Enders attenuated the virus through serial passage in human kidney cells, chicken embryo cells, and chick embryo fibroblasts—a process taking years of meticulous work.

The first measles vaccine licensed in 1963 used the Edmonston B strain but caused significant fever and rash. Maurice Hilleman further attenuated the virus, creating the Moraten strain (more attenuated Enders) with improved tolerability. Hilleman’s daughter, Jeryl Lynn, contracted mumps during this period; Hilleman isolated the virus from her throat, launching mumps vaccine development. This personal connection humanized the vaccine discovery process (PMC).

9.2. Mumps and Rubella Vaccines

Hilleman attenuated the Jeryl Lynn mumps strain through passage in embryonated hen’s eggs and chick embryo cell cultures. The resulting vaccine, licensed in 1967, proved remarkably safe and effective. Rubella vaccine development intensified after the 1964-1965 pandemic caused an estimated 20,000 cases of congenital rubella syndrome—babies born with deafness, blindness, heart defects, and intellectual disabilities.

Multiple research teams pursued rubella vaccines. Stanley Plotkin at the Wistar Institute developed the RA 27/3 strain, isolated from an aborted fetus during the 1964 outbreak. Plotkin attenuated the virus through 27 passages in WI-38 human diploid cells. His strain provided superior immunity compared to competing vaccines and became the global standard. The ethical complexity of using fetal cell lines in the vaccine discovery process sparked debates that continue today (Smithsonian).

9.3. The MMR Combination

In 1971, Maurice Hilleman combined measles, mumps, and rubella vaccines into a single injection—MMR. Combining three live viruses without interference required careful formulation and stability testing. The combination simplified vaccination schedules, improved compliance, and reduced healthcare costs. Hilleman’s achievement demonstrated how the vaccine discovery process extends beyond individual vaccines to comprehensive immunization strategies.

By the 1980s, routine MMR vaccination dramatically reduced disease incidence. Measles cases in the United States dropped from hundreds of thousands annually to mere hundreds. However, success bred complacency. When vaccination rates declined in some communities, outbreaks returned, proving herd immunity thresholds must be maintained (University of Chicago).

9.4. Global Implementation

Implementing MMR globally required Cold Chain systems, healthcare infrastructure, public education, and sustained political commitment. The Expanded Programme on Immunization (EPI), launched by WHO in 1974, coordinated global childhood vaccination. Countries adapted strategies to local contexts—some used two-dose schedules, others single-dose based on epidemiology and resources. The vaccine discovery process demonstrated that scientific breakthroughs alone cannot achieve public health impact without effective delivery systems (WHO).

10. Bacterial Capsule Vaccines

Developing vaccines against encapsulated bacteria like pneumococcus and Haemophilus influenzae type b required innovative chemistry that transformed the vaccine discovery process.

10.1. Pneumococcal Vaccine Challenges

Streptococcus pneumoniae causes pneumonia, meningitis, and bacteremia, killing hundreds of thousands annually. The bacterium’s polysaccharide capsule—its virulence factor—exists in over 90 serotypes. In 1977, Robert Austrian at the University of Pennsylvania developed a 14-valent polysaccharide vaccine covering the most common disease-causing serotypes.

Polysaccharide vaccines faced a critical limitation: they produced T-cell-independent immune responses, ineffective in children under two years—the population most vulnerable to pneumococcal disease. The vaccine discovery process required solving this immunological challenge through conjugate vaccine technology (PMC).

10.2. Hib Conjugate Technology

Haemophilus influenzae type b (Hib) caused severe meningitis, epiglottitis, and pneumonia in young children. Like pneumococcus, Hib’s polysaccharide capsule elicited poor infant immune responses. John Robbins and Rachel Schneerson at the NIH pioneered conjugate vaccine technology in the early 1980s.

Conjugation chemically links polysaccharide antigens to carrier proteins like tetanus or diphtheria toxoid. This converts T-independent antigens into T-dependent antigens, triggering robust immunity and immunological memory in infants. The first Hib conjugate vaccine licensed in 1987 revolutionized pediatric infectious disease prevention. Within years, Hib meningitis virtually disappeared in countries with vaccination programs—a stunning success in the vaccine discovery process (PMC).

10.3. Production Innovation

Pneumococcal conjugate vaccines followed, initially covering 7 serotypes (PCV7, licensed 2000), expanding to 13 (PCV13, 2010) and 15-20 valent formulations currently. Manufacturing complexity increased dramatically—each serotype requires separate fermentation, purification, conjugation, and testing. Quality control ensures correct polysaccharide-protein ratios and conjugation efficiency.

Producing conjugate vaccines costs significantly more than polysaccharide vaccines, raising access issues in low-income countries. GAVI, the Vaccine Alliance, negotiated advance market commitments with manufacturers, enabling affordable PCV access globally. This model demonstrated how the vaccine discovery process must address economic and equity dimensions alongside technical challenges (PNAS).

11. Recombinant Vaccine Technology

The emergence of biotechnology fundamentally altered the vaccine discovery process, introducing genetic engineering methods that improved safety, purity, and scalability.

11.1. Hepatitis B Breakthrough

Baruch Blumberg discovered the “Australia antigen” in 1967 while studying lipoprotein variations. He realized this antigen indicated hepatitis B virus (HBV) infection and predicted its causal relationship with liver cancer. This discovery earned him the 1976 Nobel Prize and launched the vaccine discovery process for hepatitis B.

Early hepatitis B vaccines used surface antigen purified from infected human blood—effective but concerning due to potential contamination risks. In the early 1980s, scientists at Merck, led by Hilleman, developed the first recombinant vaccine. They inserted the gene encoding HBV surface antigen into yeast (Saccharomyces cerevisiae), which produced pure antigen without infectious virus. Licensed in 1986, this recombinant vaccine eliminated blood-borne pathogen concerns and enabled unlimited production (Fox Chase Cancer Center).

Universal infant hepatitis B vaccination, implemented globally through WHO recommendations, dramatically reduced chronic infection rates and prevented liver cancer—the first cancer prevention through vaccination. Blumberg’s work exemplified how the vaccine discovery process bridges basic research and public health impact (Stanford).

11.2. Hepatitis A Development

Hepatitis A virus, causing acute liver infection through fecal-oral transmission, affected millions annually. Unlike hepatitis B, it doesn’t cause chronic infection but created significant morbidity. Maurice Hilleman and his team at Merck developed the first hepatitis A vaccine by growing virus in human cell culture, inactivating it with formaldehyde, and adding aluminum adjuvant.

Clinical trials in Thailand demonstrated high efficacy. The vaccine received FDA approval in 1995. Hilleman, who developed over 40 vaccines during his career, considered hepatitis A among his most important contributions to the vaccine discovery process. Combined hepatitis A and B vaccines followed, simplifying immunization for travelers and healthcare workers (Montana State University).

11.3. Biotechnology Revolution

Recombinant technology opened new possibilities in the vaccine discovery process: virus-like particles (VLPs) mimicking viral structure without genetic material, subunit vaccines expressing specific proteins, and vectored vaccines using harmless viruses to deliver antigens. Human papillomavirus (HPV) vaccines, preventing cervical cancer, employed VLP technology—another milestone in cancer prevention through vaccination.

The biotechnology revolution in the vaccine discovery process demonstrated that vaccines need not contain actual pathogens. Genetic information suffices to produce immunogenic molecules, improving safety profiles and enabling rapid design modification—principles that would prove crucial for COVID-19 vaccine development (PMC).

12. COVID-19 and the mRNA Revolution

The COVID-19 pandemic accelerated the vaccine discovery process in unprecedented ways, validating decades of mRNA research and demonstrating what global scientific collaboration can achieve under crisis conditions.

12.1. Decades of mRNA Research

mRNA vaccine technology wasn’t invented during COVID-19—it culminated from decades of foundational research. In the 1990s, researchers demonstrated that injecting mRNA could produce proteins in vivo, but applications remained limited due to instability, poor delivery, and inflammatory responses. Katalin Karikó, working at the University of Pennsylvania, pursued mRNA therapeutics despite consistent rejection from funders and colleagues who considered the approach impractical.

In 2005, Karikó and Drew Weissman discovered that modifying mRNA’s nucleosides—substituting pseudouridine for uridine—dramatically reduced inflammatory responses while increasing protein production. Their paper, initially overlooked, became foundational for mRNA vaccine development. Both scientists persisted despite career setbacks, demonstrating that the vaccine discovery process often requires sustained commitment through skepticism and failure (Boston University).

12.2. Katalin Karikó and Drew Weissman

Karikó’s journey epitomizes resilience in the vaccine discovery process. Demoted at Penn, denied grants repeatedly, and told to pursue “realistic” projects, she continued mRNA research driven by conviction in its potential. Drew Weissman, an immunologist studying HIV vaccines, became her essential collaborator. Their partnership combined RNA biology expertise with immunological insight.

Neither achieved immediate recognition. Karikó left Penn for BioNTech in Germany, where she served as senior vice president. When SARS-CoV-2 emerged, BioNTech partnered with Pfizer to develop an mRNA vaccine using Karikó and Weissman’s modified nucleoside technology. Similarly, Moderna employed the same principles. In October 2023, Karikó and Weissman received the Nobel Prize in Physiology or Medicine, validation arriving decades after their initial discovery (PMC).

12.3. Rapid Development and Deployment

On January 11, 2020, Chinese scientists published SARS-CoV-2’s genetic sequence. Within days, Moderna designed its vaccine. BioNTech/Pfizer followed shortly. The vaccine discovery process accelerated dramatically—vaccines moved from design through Phase 3 trials to emergency authorization in under a year, compared to typical 10-15 year timelines.

Speed didn’t compromise safety. Overlapping trial phases, advance manufacturing, global data sharing, and unprecedented funding enabled rapid progress while maintaining scientific rigor. Over 40,000 participants enrolled in Pfizer trials; Moderna enrolled 30,000. Results showed approximately 95% efficacy against symptomatic COVID-19. The FDA granted Emergency Use Authorization to Pfizer’s vaccine December 11, 2020, followed by Moderna December 18, 2020 (OSF Healthcare).

12.4. Global Distribution Challenges

mRNA vaccines require ultra-cold storage (-70°C for Pfizer’s original formulation), challenging Cold Chain logistics globally. Wealthy nations secured advance purchase agreements, acquiring most initial supply. The COVAX initiative aimed to ensure equitable access but faced funding, supply, and distribution challenges. By late 2021, high-income countries administered multiple booster doses while many low-income countries lacked first doses.

This inequality exposed limitations in the vaccine discovery process ecosystem. Scientific achievement alone doesn’t guarantee global health impact without addressing manufacturing capacity, intellectual property, technology transfer, and distribution infrastructure. The pandemic highlighted that the vaccine discovery process must integrate equity considerations from inception through delivery (Frontiers).

13. Scientists Behind the Vaccine Discovery Process

The vaccine discovery process throughout history has depended on brilliant, dedicated individuals whose persistence overcame skepticism, failures, and sometimes personal tragedy.

13.1. Edward Jenner (1749-1823)

Edward Jenner, English physician and naturalist, transformed folk wisdom into scientific practice. Beyond vaccination, he studied cuckoo bird behavior and hydrogen balloons. Despite ridicule from the medical establishment, he persisted in vaccination advocacy, personally vaccinating thousands free of charge. His systematic documentation established scientific standards. Jenner declined lucrative London practice to remain in rural Gloucestershire, prioritizing public health over personal wealth—a model of scientific service (PMC).

13.2. Louis Pasteur (1822-1895)

Louis Pasteur, French chemist and microbiologist, revolutionized medicine despite lacking medical training. His competitive nature drove breakthroughs but also controversies. Recent scholarship reveals that Pasteur sometimes exaggerated results and downplayed collaborators’ contributions. Nevertheless, his impact on the vaccine discovery process remains immense. He pioneered laboratory-based vaccine development, established the Pasteur Institute, and trained generations of microbiologists. His public demonstrations skillfully combined science and spectacle, building public trust essential for vaccination programs (Pasteur Institute).

13.3. Emil von Behring (1854-1917)

Emil von Behring, German physiologist, co-discovered diphtheria antitoxin with Shibasaburo Kitasato. Behring received the first Nobel Prize in Physiology or Medicine (1901) for this work, while Kitasato was excluded—a decision reflecting both scientific politics and racial bias. Behring’s later career involved commercial vaccine production, where profit motives sometimes conflicted with public health priorities. His complex legacy demonstrates that the vaccine discovery process exists within broader social, economic, and ethical contexts (Nobel Prize).

13.4. Maurice Hilleman (1919-2005)

Maurice Hilleman, perhaps the most prolific vaccinologist ever, developed over 40 vaccines—more than any other scientist. Born to poverty in Montana, orphaned as an infant, he earned his way through college during the Depression. At Merck, he created or improved vaccines for measles, mumps, rubella, chickenpox, meningitis, pneumonia, and hepatitis A and B. His gruff demeanor and perfectionism drove subordinates hard but ensured quality. Hilleman’s contributions to the vaccine discovery process likely saved more lives than those of any other single individual (Hilleman Film).

13.5. Baruch Blumberg (1925-2011)

Baruch Blumberg’s hepatitis B discovery emerged serendipitously from anthropological research on genetic variation. Curious about why blood transfusion recipients sometimes developed antibodies against donor antigens, he identified Australia antigen in Aboriginal blood samples. Recognizing its connection to hepatitis B took years of persistent investigation. Blumberg’s intellectual curiosity and willingness to pursue unexpected findings exemplify qualities essential to the vaccine discovery process. After his Nobel Prize, he became NASA’s chief scientist, demonstrating remarkably broad interests (Fox Chase).

13.6. Jonas Salk (1914-1995) and Albert Sabin (1906-1993)

Jonas Salk and Albert Sabin represent contrasting approaches within the vaccine discovery process. Salk, cautious and methodical, prioritized safety with his killed-virus vaccine. Sabin, more daring, pursued live-virus advantages despite greater risks. Their scientific rivalry became personal, with Sabin criticizing Salk’s vaccine as inferior. Yet both contributed enormously to polio eradication. Salk refused to patent his vaccine, declaring “Could you patent the sun?” His altruism became legendary, though some historians note commercial motives also influenced this decision. Their complex relationship illustrates that the vaccine discovery process involves human ambition, ego, and competition alongside humanitarian goals (Science History Institute).

13.7. Katalin Karikó (1955-) and Drew Weissman (1959-)

Katalin Karikó and Drew Weissman’s partnership exemplifies the vaccine discovery process requiring patience, collaboration, and faith in unconventional ideas. Karikó, Hungarian biochemist, emigrated to America with her husband and daughter, carrying $1,200 sewn into her daughter’s teddy bear to evade currency laws. Facing repeated grant rejections and institutional skepticism, she persisted through demotions and career setbacks. Weissman, educated at Boston University, shared her conviction that mRNA held therapeutic potential. Their chance meeting at a University of Pennsylvania copy machine initiated collaboration that ultimately enabled COVID-19 vaccines, demonstrating that the vaccine discovery process sometimes depends on serendipitous human connections (Lasker Foundation).

14. Clinical Trial Protocols

Rigorous clinical testing is fundamental to the vaccine discovery process, balancing the urgency of disease prevention against ethical obligations for safety and informed consent.

14.1. Early Experimental Approaches

Early vaccine experiments lacked formal ethical oversight. Jenner tested on his gardener’s son; Pasteur on a desperate boy. Such experiments would violate modern ethics, yet they occurred before regulatory frameworks existed. Benjamin Waterhouse, introducing vaccination to America, tested on his children and servants. While demonstrating conviction, these practices exemplified paternalistic medical culture with insufficient consideration of autonomy and consent. The evolution of ethical standards represents crucial progress in the vaccine discovery process (James Lind Library).

14.2. Randomized Controlled Trials

The 1954 polio trials established gold standards for the vaccine discovery process: randomization, double-blinding, placebo controls, and statistical analysis. Thomas Francis Jr.’s meticulous protocol ensured objective evaluation. Participating children received numbered vials containing either vaccine or placebo, with neither families nor administrators knowing contents. This design minimized bias and generated definitive evidence.

Subsequent vaccine trials adopted similar methodologies. Measles vaccine trials in the 1960s enrolled thousands of children; hepatitis B trials in the 1980s followed tens of thousands of healthcare workers. Each trial refined protocols: stratification by age and risk factors, active surveillance for adverse events, independent data monitoring committees, and standardized case definitions. These innovations in the vaccine discovery process balanced scientific rigor with participant safety (History of Vaccines).

14.3. Modern Fast-Track Protocols

COVID-19 vaccine trials demonstrated that the vaccine discovery process can accelerate without sacrificing safety. Adaptive trial designs allowed real-time modifications based on accumulating data. Rolling review enabled regulators to evaluate data as generated rather than after trial completion. Advance manufacturing prepared for distribution before approval, assuming financial risk to gain time.

Critics worried that speed compromised thoroughness, but trials maintained scientific standards. Phase 1, 2, and 3 studies followed established safety and efficacy endpoints. Independent data monitoring boards could halt trials for safety concerns. Long-term follow-up continues monitoring participants. The pandemic proved that the vaccine discovery process can respond rapidly to emergencies while preserving ethical and scientific integrity (OSF Healthcare).

15. Vaccine Opposition Throughout History

Opposition has accompanied the vaccine discovery process since its inception, reflecting deeper tensions about bodily autonomy, government authority, scientific trust, and medical ethics.

15.1. Religious and Philosophical Opposition

Jenner’s smallpox vaccine faced religious objections that vaccination defied divine will—if God sent disease, humans shouldn’t prevent it. Clergy preached that vaccination interfered with God’s plan. Political cartoons depicted vaccination causing people to grow cow parts. These anxieties, while appearing irrational today, reflected genuine theological concerns within religious frameworks. Some religions permitted vaccination as preserving life (a higher commandment), while others condemned it as unnatural intervention. These debates established patterns recurring throughout the vaccine discovery process (History of Vaccines).

15.2. 19th Century Anti-Vaccination Movements

Compulsory vaccination laws sparked organized resistance. The 1853 Vaccination Act in England mandated childhood smallpox vaccination, with fines or imprisonment for refusal. Working-class parents resented government intrusion and medical authority. The Anti-Vaccination League formed, organizing protests and publishing literature. Leicester, a major city, largely rejected vaccination, implementing sanitation and quarantine instead during outbreaks—with mixed results.

Vaccination critics raised legitimate concerns: contamination risks, lack of quality control, and government overreach. The 1898 Vaccination Act added conscience clauses allowing exemptions, acknowledging individual rights within public health policy. This tension between collective protection and personal autonomy continues shaping debates around the vaccine discovery process (History of Vaccines).

15.3. Modern Vaccine Hesitancy

Modern vaccine hesitancy gained prominence with the fraudulent 1998 Wakefield study falsely linking MMR vaccine to autism. Despite retraction and Andrew Wakefield’s medical license revocation, the damage persists. Parent advocacy groups, celebrity endorsements, and social media amplified these discredited claims. Measles outbreaks returned in communities with low vaccination rates, causing preventable deaths.

Vaccine hesitancy encompasses a spectrum from those with specific concerns to committed anti-vaccine activists. Psychological research identifies various motivations: distrust of pharmaceutical companies, preference for “natural” immunity, libertarian political philosophy, and conspiracy theories. Addressing hesitancy requires empathetic engagement rather than dismissal, recognizing that trust-building is essential to the vaccine discovery process success (PMC).

15.4. Social Media Impact

Social media transformed vaccine discourse. Misinformation spreads rapidly, algorithms create echo chambers, and emotional anecdotes outcompete statistical evidence. During COVID-19, conspiracy theories proliferated: vaccines contained microchips, altered DNA, or caused infertility—all demonstrably false yet widely believed.

Public health authorities struggled to counter misinformation effectively. Traditional communication strategies proved inadequate for digital environments. Some platforms implemented fact-checking and content moderation, raising free speech concerns. The vaccine discovery process must now incorporate digital communication strategies, recognizing that scientific achievement alone cannot ensure public acceptance without effective, transparent, and empathetic communication (PMC).

16. Technology and Social Change

Modern technology profoundly influences every stage of the vaccine discovery process, from antigen discovery through post-market surveillance and public communication.

16.1. Genomic Surveillance

Rapid genome sequencing revolutionized the vaccine discovery process. SARS-CoV-2’s genetic sequence, published January 11, 2020, enabled vaccine design within days. Global networks like GISAID facilitate real-time viral sequence sharing, tracking mutations and variant emergence. This genomic surveillance guides vaccine updates, monitors breakthrough infections, and predicts evolutionary trajectories.

Next-generation sequencing technologies enable comprehensive pathogen characterization, identification of conserved epitopes for universal vaccines, and understanding of host immune responses at molecular levels. Bioinformatics and computational modeling predict immunogenicity, optimize antigen design, and accelerate the vaccine discovery process dramatically compared to historical trial-and-error approaches (Frontiers).

16.2. Artificial Intelligence

Machine learning algorithms analyze vast datasets to identify vaccine candidates, predict protein structures, optimize manufacturing processes, and forecast epidemic trajectories. AI-driven approaches in the vaccine discovery process include: epitope prediction identifying which pathogen fragments trigger immune responses, structural biology predicting how antigens fold and interact with antibodies, clinical trial optimization identifying ideal participant populations and dosing regimens, and supply chain management ensuring vaccine distribution efficiency.

While AI accelerates discovery, it cannot replace human judgment in ethical decisions, clinical interpretation, and public health strategy. The vaccine discovery process increasingly integrates AI as a powerful tool within broader scientific and social contexts (PMC).

16.3. Digital Communication

Digital technology transforms vaccine acceptance and uptake. Mobile apps remind individuals of vaccination appointments, track immunization records, and report adverse events. Telemedicine facilitates vaccine counseling. Social media campaigns promote vaccination—though also spread misinformation. WhatsApp and text messaging enable community health workers to reach remote populations.

During COVID-19, vaccine appointment systems overwhelmed with demand, highlighting digital divide issues—disadvantaged populations lacking internet access faced barriers. The vaccine discovery process must address how technological solutions can inadvertently worsen health inequities, ensuring that digital innovations enhance rather than replace accessible, human-centered public health infrastructure (OSF Healthcare).

17. Barriers in the Vaccine Discovery Process

Despite remarkable progress, the vaccine discovery process confronts persistent scientific, technical, social, and structural barriers that constrain its effectiveness and reach.For example, in rural areas of Africa and Asia, limited transportation infrastructure and cold chain availability often hinder vaccination campaigns, despite global funding efforts.

17.1. Scientific Uncertainties

Many pathogens remain without effective vaccines despite decades of research. HIV’s extreme genetic variability, latency, and immune evasion mechanisms have defeated vaccine development for 40 years. Malaria’s complex life cycle and parasitic nature pose unique immunological challenges. Tuberculosis vaccines provide incomplete protection. These failures humble scientific confidence and demonstrate that the vaccine discovery process, despite sophistication, cannot yet solve all infectious disease challenges. Understanding protective immunity requires ongoing basic research into immunology, pathogen biology, and host-pathogen interactions (PMC).

17.2. Pathogen Variability

Viral and bacterial evolution constantly challenges the vaccine discovery process. Influenza’s antigenic drift necessitates annual vaccine updates. SARS-CoV-2 variants reduced vaccine effectiveness, requiring booster modifications. Bacterial pathogens like pneumococcus present dozens of serotypes; vaccines covering some serotypes exert selective pressure, potentially increasing non-vaccine serotypes (serotype replacement). Developing broadly protective or universal vaccines targeting conserved pathogen features represents a major frontier, but achieving this goal requires fundamental immunological breakthroughs (Frontiers).

17.3. Manufacturing and Distribution

Scaling laboratory discoveries to billions of doses presents enormous challenges in the vaccine discovery process. Manufacturing requires specialized facilities, skilled workforce, quality control systems, and regulatory compliance. Supply chains involve raw materials, adjuvants, vials, syringes, and packaging. Cold chain requirements—especially for mRNA vaccines—demand reliable refrigeration from factory to patient.

Distribution challenges intensify in resource-limited settings with inadequate infrastructure. Last-mile delivery to remote villages, maintaining cold chains without electricity, and training healthcare workers require creative solutions. The vaccine discovery process extends beyond scientific innovation to implementation science, addressing real-world constraints that determine whether vaccines actually reach those who need them (Proclinical).

17.4. Ethical and Social Challenges

Ethical complexities permeate the vaccine discovery process. Clinical trials in developing countries raise exploitation concerns—do communities hosting trials benefit from resulting vaccines? Pregnancy exclusions from trials delay safety data for pregnant individuals, leaving them unprotected. Placebo controls in outbreak contexts present ethical dilemmas when untreated participants face disease risk. Balancing speed against thoroughness tests ethical principles.

Social challenges include vaccine hesitancy, cultural beliefs affecting acceptance, gender inequities in healthcare access, and political factors influencing distribution. Addressing these requires community engagement, cultural competence, transparent communication, and recognition that scientific evidence alone doesn’t ensure vaccine uptake. The vaccine discovery process must integrate social science insights alongside biological research (OSF Healthcare).

17.5. Global Access and Equity

Vaccine inequity remains perhaps the greatest failure in the vaccine discovery process. COVID-19 starkly illustrated this: high-income countries administered multiple boosters while low-income countries struggled to obtain first doses. Intellectual property protections, limited manufacturing capacity, advance purchase agreements, and export restrictions all contributed to inequity.

COVAX, established to ensure equitable access, fell short of goals due to insufficient funding, supply shortages, and nationalistic policies. Technology transfer initiatives face resistance from pharmaceutical companies protecting commercial interests. The vaccine discovery process increasingly recognizes that scientific and manufacturing challenges pale beside political and economic barriers to truly global immunization. Solving these requires international cooperation, political will, and rethinking intellectual property frameworks for essential medicines (Frontiers).

18. The Future of the Vaccine Discovery Process

The vaccine discovery process continues evolving rapidly, with emerging technologies and changing disease landscapes shaping future directions.

18.1. Universal Vaccines

Universal flu vaccines targeting conserved viral regions could provide multi-year or lifetime protection, eliminating annual reformulation needs. Multiple candidates are in clinical trials, focusing on hemagglutinin stem regions or internal proteins like nucleoprotein and M2. Success would transform influenza prevention, though achieving sufficient breadth and durability remains challenging. Similar approaches target broadly neutralizing HIV epitopes, though HIV’s extreme variability complicates development.

Pan-coronavirus vaccines protecting against multiple coronavirus species could prevent future pandemics. These efforts in the vaccine discovery process exemplify rational design based on structural biology and immunology, contrasting with earlier empirical approaches. Success could establish templates for universal vaccines against other pathogen families (PMC).

18.2. Personalized Immunization

Genomic and immunological profiling may enable personalized vaccination strategies. Some individuals respond poorly to standard vaccines due to genetic factors or immune status; personalized approaches could optimize their protection. Cancer vaccines, designed to target patient-specific tumor antigens, represent extreme personalization. mRNA technology facilitates such customization, rapidly producing tailored vaccines.

Personalized immunization in the vaccine discovery process raises logistical and equity concerns—will such approaches be accessible globally, or only to wealthy populations with advanced healthcare? Balancing innovation with equity requires careful consideration (OSF Healthcare).

18.3. Next-Generation Platforms

Self-amplifying RNA vaccines use viral replication machinery to produce sustained antigen expression from smaller doses. DNA vaccines deliver genes using electroporation or nanoparticles. Viral vectors like modified adenoviruses or measles viruses carry vaccine antigens. Each platform offers distinct advantages: thermostability, manufacturing simplicity, or immune response profiles.

Infographic comparing mRNA, DNA, viral vector, protein subunit, and self-amplifying RNA vaccine platforms with icons and bullet points.

Nanoparticle vaccines displaying multiple antigens in precise arrays may enhance immunity. Microarray patches delivering vaccines painlessly through skin could simplify administration. Plant-based vaccine production offers rapid, inexpensive manufacturing. These innovations in the vaccine discovery process expand possibilities, though each requires validation through clinical trials and regulatory approval (Frontiers).

19. Conclusion

The vaccine discovery process stands as one of humanity’s greatest intellectual and humanitarian achievements. From Jenner’s cowpox experiments to Karikó’s mRNA breakthroughs, each advance built upon previous knowledge while overcoming skepticism, failure, and opposition. Vaccines have eradicated smallpox, nearly eliminated polio, and helped prevent HPV and hepatitis B virus–related cancers, substantially reducing these cancer incidences where vaccination is widespread ([WHO], [Britannica]).

Yet the vaccine discovery process remains incomplete. HIV, malaria, tuberculosis, and emerging pathogens require continued innovation. Vaccine inequity denies billions of people protection available to others. Anti-vaccine movements threaten hard-won progress. Climate change, urbanization, and ecological disruption create conditions for novel infectious disease emergence.

Future success in the vaccine discovery process demands not only scientific innovation but also ethical integrity, global cooperation, public engagement, and commitment to equity. The scientists profiled here—Jenner, Pasteur, Behring, Hilleman, Blumberg, Salk, Sabin, Karikó, Weissman, and countless unnamed researchers—demonstrated that persistence through adversity, intellectual curiosity, and dedication to public good can overcome seemingly insurmountable challenges. Their legacy inspires continued efforts to protect human health through the vaccine discovery process for generations to come.

What are your thoughts on universal vaccine development? Would you participate in future vaccine trials if given the opportunity?

20. Sources

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