Poliomyelitis, commonly known as polio or infantile paralysis, is an infectious disease caused by the poliovirus. The virus spreads from person to person and can infect a person’s spinal cord, causing paralysis (can’t move parts of the body). Polio was once one of the most feared diseases in industrialized countries, paralyzing hundreds of thousands of children and adults throughout the 20th century.
While there is no cure for polio, it has been mostly eradicated thanks to extensive international vaccination efforts. Polio immunization programs, using both killed/inactivated and live/attenuated oral poliovirus vaccines, have reduced polio cases globally by over 99% since the World Health Organization (WHO) began a global polio eradication initiative in 1988. As a result of this initiative, only Afghanistan and Pakistan have never stopped transmission of the wild poliovirus.
History of Polio
There is evidence that polio has existed for thousands of years. Epidemics became more frequent in the late 19th century, primarily in temperate industrialized regions. Major outbreaks occurred in Scandinavia (1889), United States (1894), and then Europe and the United States(1907-1908, 1916, and 1950 in the U.S.). Common modes of spread included direct person-to-person transmission or through contact with infected fecal matter.
To help better understand transmission, researcher Karl Landsteiner (1868-1943) first identified the three types of poliovirus in monkeys in 1909. This seminal discovery helped distinguish the strains and facilitated vaccine development. Meanwhile, affected individuals tried to cope with a disease that had no cure. Iron lungs helped those paralyzed breathe, while news of epidemics among children spread widespread fear among families in the 1940s-1950s.
The 1952 polio epidemic in the United States was its worst ever, with more than 57,000 cases reported. This crisis helped galvanize research efforts and public demand for a vaccine. Prominent American researcher Jonas Salk developed the first effective inactivated (killed) polio vaccine with clinical trials starting in 1954. It was licensed for use in 1955 and helped dramatically curb transmission that year. Over 35 million children received the Salk vaccine between 1955-63 decreasing disease rates by over 80%.
Meanwhile, Albert Sabin developed an attenuated (weakened) live oral poliovirus vaccine in the late 1950s that was easier to administer. Initially used widely in Cuba, Mexico, and Soviet bloc nations, it was licensed in the U.S. in 1962. The Sabin vaccine has since become the main polio vaccine globally due to lower cost, not needing trained staff, and conferring wider intestinal immunity to curb person-to-person transmission. This helped many nations eliminate endemic transmission by the 1990s.
Global Eradication Campaign
With most industrialized nations polio-free into the 1960s/70s, the WHO established the Expanded Program on Immunization in 1974 to help other nations immunize children. Yet polio remained endemic in developing countries. After declaration of polio eradication as a global goal in 1988, the WHO established the Global Polio Eradication Initiative to coordinate worldwide vaccination campaigns.
This vast undertaking involved over 20 million volunteers immunizing almost every child under 5 worldwide. Challenges included difficult terrain, conflict areas, vaccine hesitancy, and reaching isolated communities. Nations needed to maintain very high vaccine coverage rates(>80%) to interrupt transmission chains and prevent importation. Biosecurity measures also became important, with stringent containment of wild and attenuated strains in certified labs to avoid accidental release that could restart epidemics.
Successes and Setbacks
The campaign has achieved immense progress. Once over 350,000 cases occurred annually across 125 endemic countries in the late 1980s. In 2015, just 74 cases remained in only Afghanistan, Pakistan, and Nigeria. By 2019, Nigeria was declared polio-free with only wild poliovirus type 1 remaining globally. Conflict areas made progress difficult in Afghanistan and Pakistan.
Additionally, cessation of oral polio vaccine use in some nations led to rare vaccine-derived polio outbreaks. This can occur when live weakened virus in OPV mutates and circulates in under-immunized communities, regaining virulence. So-called cVDPV type 2 paralyzed over 450 people in the Democratic Republic of Congo from 2019-2021, highlighting risks if high vaccination rates aren’t maintained everywhere.
The pandemic also led nations to redirect resources away from immunization, leading to surges in other diseases like measles. Yet coordination between multiple partners remains focused on completing eradication in the last endemic countries. Continued outbreak response immunization in previously polio-free areas is also critical to avert resurgence. With efforts to reach every last child, the hope remains to stop all polio transmission globally in the foreseeable future. This achievement would rank among the greatest victories in biomedical science, saving millions from lifelong paralysis each generation into the future.
Through extensive coordinated immunization worldwide since 1988, the global polio eradication campaign has made tremendous progress against one of the most feared childhood infections of the 20th century. While challenges remain to fully interrupt transmission in conflict-hit areas, success would ensure future generations never experience the crippling effects of wild poliovirus. The achievement would stand as a shining example of global cooperation in international public health.
Andrew Stroud