Download the full article (PDF)
How Vaccines Against Smallpox and Polio Reshaped Human Civilization

Introduction

Infectious diseases have shaped human civilization for millennia, often determining the fate of societies, economies, and populations. Among the countless pathogens that have afflicted humanity, two stand apart in both their devastation and their eventual conquest: Smallpox and Poliomyelitis (Polio). The eradication of smallpox and the near-eradication of polio are landmark achievements in public health, marking humanity’s progress from helplessness before invisible enemies to mastery through science and collective global action. These successes represent not only triumphs of medical innovation but also of international cooperation, epidemiological surveillance, and societal will. Together, they demonstrate how vaccines have transformed global mortality patterns, saved hundreds of millions of lives, and reshaped the course of human health and development.

Smallpox: The First Eradicated Human Disease

Pathophysiology of Smallpox Smallpox, caused by the Variola major virus, was one of history’s most lethal infectious diseases. The virus spread through respiratory droplets and direct contact with contaminated objects or individuals. After inhalation, it replicated in the respiratory epithelium and regional lymph nodes, followed by a viremia that disseminated the virus to the skin, mucous membranes, and internal organs. The disease presented as high fever, malaise, and a progressive pustular rash covering the entire body. The hallmark pathologic process involved extensive viral replication in dermal and mucosal epithelial cells, resulting in necrosis, inflammatory infiltration, and scarring. Severe systemic infection frequently led to multiorgan involvement and septic shock. The average mortality rate was 30%, but in severe cases such as Variola major confluent type, mortality could reach 60–80%. Survivors were often left blind or disfigured. Epidemiology and Prevalence Before Vaccination Before vaccination, smallpox caused an estimated 300 million deaths during the 20th century. Various sources, including the World Health Organization and historical data, consistently report this figure, reflecting the severe impact of the disease worldwide before its eradication by vaccination efforts. Over a longer span, smallpox is estimated to have caused about 300 – 500 million deaths in the last hundred years of its existence (1). Outbreaks occurred cyclically in Europe, Asia, Africa, and the Americas, with no continent spared. In the 1900s, mortality rates in endemic countries such as India and China exceeded 10 million per decade. The disease struck indiscriminately, but the most affected populations were infants, children, and the urban poor living in crowded conditions. In rural regions with limited access to healthcare, fatality rates were especially high due to the lack of supportive care. Development of the Vaccine The origins of vaccination trace to Edward Jenner, an English physician and natural philosopher working at St. George’s Hospital in the late 18th century. In 1796, Jenner demonstrated that inoculation with cowpox lesions conferred immunity to smallpox, a revolutionary finding that led to the world’s first vaccine. Although Jenner lived long before the establishment of the Nobel Prize (1901), his work is recognized as the foundation of immunology. Throughout the 19th and 20th centuries, the vaccine underwent refinements, with freeze-dried formulations introduced in the 1950s to allow global distribution. Global Eradication Campaign In 1967, the World Health Organization (WHO) launched the Global Smallpox Eradication Program, spearheaded by epidemiologists such as Donald A. Henderson of the U.S. Centers for Disease Control and Prevention (CDC). The strategy involved mass vaccination and ring vaccination, the immunization of all contacts of identified cases, to interrupt transmission chains. Through unprecedented international cooperation, the program distributed millions of doses worldwide, employing local health ministries, mobile vaccination teams, and community-based campaigns. The last reported case of smallpox in the United States occurred in 1949. The final naturally occurring worldwide   case was reported in Somalia in 1977, and in 1980, smallpox was officially declared eradicated by the WHO.  Current Status Today, Variola virus exists only in two high-security laboratories, one at the CDC (United States) and another at the VECTOR Institute (Russia), maintained for research and biodefense. Routine vaccination ceased after eradication, though smallpox remains a model organism for understanding viral pathogenesis and vaccine-induced immunity. Estimated Global Deaths Prevented (1900–2025) If smallpox vaccination had never been developed or implemented, global demographic models estimate between 400 and 500 million additional deaths by 2025, assuming historic mortality rates and population growth.

Poliomyelitis: The Near-Eradication of a Paralytic Disease

Pathophysiology of Poliomyelitis Polio, caused by the poliovirus (an enterovirus of the Picornaviridae family), spreads primarily through the fecal–oral route. After ingestion, the virus replicates in the intestinal mucosa and can enter the bloodstream, occasionally invading the central nervous system (CNS). There, it selectively destroys motor neurons in the anterior horn of the spinal cord and brainstem, leading to paralysis, muscle atrophy, and respiratory failure.  While most infections are asymptomatic, about 1 in 200 infections leads to irreversible paralysis, and among those paralyzed, 5–10% die when respiratory muscles become immobilized. The most severe form, bulbar polio, affects the brainstem, often necessitating the use of mechanical ventilators (the “iron lung”). Epidemiology and Prevalence Before Vaccination By the early 20th century, polio had become a global health crisis, particularly in industrialized nations. Outbreaks swept across North America and Europe in recurring summer epidemics, paralyzing tens of thousands of children annually. In 1952, the United States recorded over 58,000 cases, with more than 3,000 deaths in a single year. Globally, over 500,000 new cases were estimated each year prior to vaccine availability.  The disease was especially prevalent in the United States, United Kingdom, India, Pakistan, Nigeria, and Egypt, regions where sanitation challenges or population density facilitated viral spread. Children under the age of five were the most vulnerable, but adolescents and young adults could also suffer severe outcomes.  Development of the Vaccine The first successful inactivated poliovirus vaccine (IPV) was developed in 1952 by Dr. Jonas Salk, a medical researcher at the University of Pittsburgh. In 1955, the vaccine underwent large-scale trials involving 1.8 million children and was declared safe and effective. Shortly thereafter, Dr. Albert Sabin at the University of Cincinnati developed the oral poliovirus vaccine (OPV) in 1961, which used live attenuated virus strains. Both vaccines were distributed globally through partnerships between governments, the WHO, and philanthropic organizations. Neither Salk nor Sabin received the Nobel Prize, though both were recognized with numerous scientific honors and humanitarian awards. Distribution and Global Eradication Efforts The Global Polio Eradication Initiative (GPEI) was launched in 1988 by the WHO, UNICEF, Rotary International, and the CDC. This coalition coordinated mass vaccination campaigns, reaching even the most remote regions through door-to-door immunization drives.  The result has been a 99.9% reduction in global cases, from an estimated 350,000 annual cases in 1988 to fewer than 200 in 2024. Endemic transmission now persists only in parts of Afghanistan and Pakistan, largely due to conflict and logistical barriers to vaccine delivery. Current Status Polio has been eradicated from the Americas (1994), Europe (2002), Western Pacific (2000), Southeast Asia (2014), and Africa (2020). Only isolated cases of vaccine-derived poliovirus occasionally emerge, which are carefully contained through rapid immunization responses. Estimated Global Deaths Prevented (1900–2025) If polio vaccines had not been developed, the cumulative burden from 1900–2025 is estimated to include over 20 million cases of paralysis and 5–6 million deaths globally, based on historic incidence and case-fatality rates.

Discussion and Global Significance

The eradication of smallpox and near-eradication of polio represent the pinnacle of vaccine-driven public health. Both diseases were once universal threats, transcending geography, class, and culture. Their conquest was made possible through several key innovations: the establishment of national immunization programs, advances in cold-chain logistics, international data sharing, and the commitment of countless health workers worldwide. From a biological perspective, these achievements demonstrate how targeting pathogen-specific immune mechanisms can lead to complete global disease suppression. From a societal perspective, they highlight how public trust in vaccination and government coordination are indispensable to success. The estimated combined death toll prevented by smallpox and polio vaccines from 1900–2025 exceeds 410 million lives—a figure that dwarfs the death toll of any single conflict or natural disaster in human history.

Conclusion

The elimination of smallpox and the near-eradication of polio underscore the transformative power of science when aligned with global cooperation. Edward Jenner’s 18th-century innovation, Jonas Salk’s and Albert Sabin’s 20th-century breakthroughs, and the coordinated campaigns of the WHO and CDC in the 20th and 21st centuries collectively redefined the boundaries of medicine and humanity’s capacity to control disease. As the world faces emerging pathogens and vaccine hesitancy in the modern era, the legacies of smallpox and polio vaccination remind us that the tools for ending pandemics already exist. The challenge, as ever, lies in our collective will to use them, guided by evidence, solidarity, and an unrelenting commitment to the preservation of human life.

Reference

  • Bourré L., et al. “The history of smallpox: A review of the clinical disease and vaccination.” Frontiers in Microbiology. 2023;14:1255935. doi:10.3389/fmicb.2023.1255935.
  Disclaimer: This blog post is intended solely for educational and scientific informational purposes. Any mention of therapeutic drug names, including FDA-approved medications, is for the purpose of accurate reporting and discussion of biomedical research and does not constitute medical advice, endorsement, or promotion. Readers should not interpret the content as a recommendation for any specific treatment. Always consult a qualified healthcare professional for medical advice or treatment decisions.  

About Marin Biologic Laboratories

Our Recent Publication/Meeting Presentation on Gene Therapy

1. Development of VNX-101, an Adeno-Associated Virus with Less Immunogenicity and Efficient Long-Term Expression of a CD19 T-Cell Engager. Molecular Therapy Methods & Clinical Development, published online July 24, 2025.

2. Development of a Pharmacokinetic (PK) Mouse Serum GLP ELISA for an Anti–CD19–AntiCD3 Diabody bioRxiv 2025.03.19.644217; doi: https://doi.org/10.1101/2025.03.19.644217.

3. Cell-Based Potency Assay for Anti-CD3-Anti-CD19 Diabody. bioRxiv 2025.04.15.648836v1 https://www.biorxiv.org/content/10.1101/2025.04.15.648836v1.

4. American Society of Hematology (ASH) Annual Meeting 2024. Abstract link: Using Gene Therapy to Solve Challenges with CAR-T Cell Immunotherapy: Lead Selection and Preclinical Development of an Adeno-Associated Virus with Reduced Immunogenicity Exhibiting Efficient and Long-Term Expression of an Anti-CD19 T-Cell Engager.

Comprehensive Assay Solutions for In Vitro and Cell Based Potency Assays and Pharmacokinetics Studies- Our Expertise

With 30 years of expertise in cell culture, cell-based assays, and preclinical/clinical PK/PD analysis, we specialize in offering assay services essential for a wide variety of therapeutic drug development programs, preclinical studies, IND/BLA applications, and commercialization. Our comprehensive services include both preclinical non-GLP and GLP assays, as well as non-GMP and GMP assays, providing critical support throughout the entire development pipeline. Watch the following video and explore our latest presentation on the development and validation of potency and pharmacokinetic (PK) assays for AAV vectors, highlighting innovative methodologies and industry-leading expertise.  
 

Download the full presentation: Development of Custom Cell Based and In vitro Potency and Pharmacokinetics (PK) Assays for AAV vectors- Marin biologic Laboratories

 

Development of Cell-Based Potency Assays: Case Studies and Blogs from Marin Biologic Laboratories (MarinBio)

 

Drug Discovery & Development Assays Offered by Marin Biologic Laboratories (MarinBio)