Polio vaccine

• 1. Introduction

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  In 1988 polio paralysed an estimated 350,000 people in a single year. By 2018 the worldwide count of reported cases had fallen to 33. That collapse, from hundreds of thousands to a handful, is the work of the polio vaccine. It exists in two very different forms. One is an inactivated poliovirus delivered by injection, known as IPV. The other is a weakened live virus swallowed by mouth, known as OPV. The World Health Organization recommends that every child be fully vaccinated against the disease, and it lists the vaccine among its essential medicines. Yet the path to those two vials runs through ground monkey spinal cords, a man who tested his brew on his own children, a meeting where one scientist was called a murderer, and a contaminated batch that paralysed children it was meant to protect. How did a medicine this dangerous to make become the tool that nearly erased a disease? And why, decades later, do gunmen still shoot the people who carry it?

• 2. Two Vaccines, Two Bargains

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  Injection or drops: the choice between IPV and OPV is a trade between safety and reach. After two doses of the inactivated injected vaccine, 90% or more of people develop protective antibodies to all three serotypes of poliovirus, and at least 99% are immune after three doses. The killed virus carries almost no risk of causing the disease, which is why IPV replaced the oral vaccine in many developed countries during the 1990s. Its weakness is logistical. It needs sterile syringes and trained hands. The oral vaccine answers that problem. It needs no syringe, no special equipment, and no extensive training, which makes it the natural fit for mass campaigns. One dose of trivalent OPV produces immunity to all three serotypes in roughly 50% of recipients, and three doses push that past 95%. OPV also builds immunity in the intestine, the primary site where wild poliovirus enters, and that gut defence helps block infection where the virus is endemic. There is an unusual bonus. The attenuated virus is excreted for a few days after vaccination, so it can pass to unvaccinated people nearby and immunise them too, quietly amplifying every dose delivered. The oral vaccine carries one inherent danger that the next chapter examines in full.

• 3. When The Cure Reverts

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  Roughly one person in every 2.7 million doses of the Sabin oral vaccine develops vaccine-associated paralytic poliomyelitis, with symptoms identical to wild polio. The live virus is the source of that risk. In under-vaccinated populations it can keep circulating, mutate over time, and revert to a neurovirulent form, a strain known as circulating vaccine-derived poliovirus, or cVDPV. This reversal takes considerable time and does not harm the person who was first vaccinated. It threatens those around them. In 2017, with wild polio cases at record lows, the world crossed a strange threshold. For the first time, more cases came from vaccine-derived poliovirus than from the wild virus itself. A change in the vaccine recipe sharpened the problem. After wild poliovirus type 2 was completely eradicated, the trivalent oral vaccine was phased out in 2016 and replaced with a bivalent version covering only types 1 and 3. The resulting gap in type 2 immunity, among other factors, fed outbreaks of cVDPV type 2, which rose from two cases in 2016 to 1037 cases in 2020. The response was a redesigned oral vaccine, nOPV2, genetically modified to resist the mutations that turn it dangerous. It won emergency licensing in 2021 and full licensure in December 2023. Stabilised versions targeting types 1 and 3 are now in development, meant eventually to replace the Sabin vaccines entirely.

• 4. Witches Brew And Bath Tub Gin

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  In 1932 John A. Kolmer began grinding the spinal cords of infected monkeys, soaking them in salt solution, filtering the mix through mesh, treating it with ricinolate, and refrigerating it for fourteen days. Critics later called his methods hair-raisingly amateurish, the therapeutic equivalent of bath-tub gin, and the result a veritable witches brew. After a small trial in 42 monkeys, Kolmer turned to people in 1934, testing the live attenuated vaccine on himself, his two children, and his assistant. He gave it to only 23 more children before declaring it safe and shipping it to doctors. By November 1935 he reported vaccinating 446 children and adults, and noted that 12,000 doses had been distributed to some 700 physicians across the United States and Canada, with no instructions on how to administer it or report harm. At least ten cases of paralytic polio followed his vaccine, six of them fatal, several in towns with no outbreak. At nearly the same time, Maurice Brodie took the opposite approach. Working with William H. Park at the New York City Health Department, and funded by the President's Birthday Ball Commission, Brodie built a killed-virus vaccine, settling on formaldehyde to inactivate the ground cords. He published his first success in three monkeys on the 1st of June 1934, then experimented on himself and his co-workers. Twelve children in a New York City asylum were quietly subjected to early safety trials. When a severe outbreak hit Kern County, California, over 1,500 doses were administered there between November 1934 and May 1935. Brodie's broader field study reached 9,000 vaccinated children against 4,500 matched controls. Park, described as never one to let grass grow under his feet, declared the vaccine safe. The reckoning came at a meeting in another city.

• 5. The Murderer Accusation

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  In October 1935, at the American Public Health Association's annual meeting in Milwaukee, Wisconsin, both rivals were called to present, with Thomas M. Rivers brought in to critique each paper. The fight broke open at a follow-up symposium the next month. James Leake of the U.S. Public Health Service rose with clinical evidence that the Kolmer vaccine had caused several deaths, and allegedly accused Kolmer of being a murderer. Rivers later recalled it in his oral history. All hell broke loose, and it seemed as if everybody was trying to talk at the same time, he said, adding that Leake used the strongest language he had ever heard at a scientific meeting. Brodie stood and said it looked as though, according to Dr. Rivers, his vaccine was no good, and according to Dr. Leake, Dr. Kolmer's was dangerous. Kolmer answered simply. Gentlemen, this is one time I wish the floor would open up and swallow me. Kolmer's live vaccine had already been withdrawn in September 1935. Brodie's was judged safe but doubtful in efficacy, and after three children developed paralytic polio following a dose, the Warm Springs Foundation in Georgia requested its withdrawal in December 1935. The careers diverged sharply. Kolmer, already established, returned to Temple University and worked productively until retiring in 1957. Brodie, the lesser-known man who may have built an effective vaccine, was fired within three months of the symposium's publication and died of a heart attack three years later, at age 36. His formalin-inactivated method later became the basis for the Salk vaccine, a debt he never lived to see honoured.

• 6. Growing The Virus

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  A leftover handful of test tubes changed everything in March 1948. Thomas H. Weller was trying to grow varicella virus in embryonic lung tissue when he noticed a few unused tubes. On a chance, he added a sample of poliovirus-infected mouse brain to them. The varicella cultures failed; the polio cultures grew. The research group, headed by John Enders at the Children's Hospital Boston and including Weller and Frederick C. Robbins, had cracked how to cultivate poliovirus in human tissue in the laboratory. The achievement earned the three men the Nobel Prize in Physiology or Medicine in 1954. Their breakthrough joined other key advances: the identification of three poliovirus serotypes, the finding that the virus must be present in the blood before paralysis, and proof that gamma globulin antibodies could protect against paralytic polio. This new ability to grow the virus opened the door that two decades of moratorium had kept shut.

• 7. Salk And The Largest Trial

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  On the 26th of March 1953, Jonas Salk went on CBS radio to report a successful test on a small group of adults and children, with results published in JAMA two days later. Salk and his University of Pittsburgh team, which included Julius Youngner, Byron Bennett, L. James Lewis, and Lorraine Friedman, had developed the first effective polio vaccine in 1952, a killed-virus injectable. Leone N. Farrell invented a laboratory technique in Toronto that made mass production possible. The early-1950s setting gave the work urgency. U.S. polio rates ran above 25,000 a year, spiking to 58,000 cases in 1952 and 35,000 in 1953, with 3,200 and 1,400 deaths in those years. Beginning the 23rd of February 1954, the vaccine was tested at Arsenal Elementary School and the Watson Home for Children in Pittsburgh. Then came the Francis Field Trial, led by Thomas Francis, the largest medical experiment in history at that time. It started with about 4,000 children at Franklin Sherman Elementary School in McLean, Virginia, and grew to 1.8 million children across 44 states from Maine to California. Roughly 440,000 received injections, about 210,000 got a placebo of harmless culture media, and 1.2 million were unvaccinated controls. The results were announced on the 12th of April 1955, the tenth anniversary of the death of President Franklin D. Roosevelt. The vaccine was 60-70% effective against poliovirus type 1, over 90% against types 2 and 3, and 94% against bulbar polio. After licensing in 1955 and a March of Dimes campaign, U.S. cases fell from 35,000 in 1953 to 5,600 by 1957, and to just 161 by 1961. A week before the trial results, Pierre Lepine at the Pasteur Institute in Paris had announced his own effective vaccine.

• 8. Cutter, Sabin, And Eradication

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  In April 1955, weeks after mass vaccination began, the Surgeon General started receiving reports of children contracting paralytic polio about a week after their shots, with paralysis starting in the injected limb. The vaccine came from the Cutter pharmaceutical company, which had inoculated 409,000 children across the western and midwestern United States. Investigators found that some lots from Cutter, Wyeth, and other labs had not been properly inactivated, letting live virus into more than 100,000 doses. The Cutter vaccine alone caused 260 cases of polio and killed 11. The Surgeon General pulled all Cutter vaccines, and in May 1955 a Technical Committee on Poliomyelitis Vaccine was established to review every lot. The incident drained public confidence and dropped vaccination rates. That damaged trust opened a door for Albert Sabin. Because America was committed to the Salk vaccine, Sabin tested his live oral vaccine in Mexico and the Soviet Union, while Hilary Koprowski tested his in the Congo and Poland. In 1957 Sabin developed a trivalent oral vaccine covering all three poliovirus types. In 1959 ten million children in the Soviet Union received it, and for that work Sabin was given the Order of Friendship of Peoples, described as the Soviet Union's highest civilian honour. His oral vaccine reached commercial use in 1961 and soon supplanted Salk's tarnished injection. The global eradication effort, launched in 1988 by the WHO, UNICEF, and the Rotary Foundation, leaned heavily on the oral vaccine developed by Sabin and Mikhail Chumakov. Polio was eliminated in the Americas by 1994, across 36 Western Pacific countries including China and Australia by 2000, and in Europe by 2002. India recorded no cases after January 2011 and was declared polio-free in March 2014. The last holdouts proved to be the hardest. In Pakistan and Afghanistan, the only countries with wild polio as of 2020, a fringe belief that the vaccine secretly sterilises Muslims persists, deepened by the CIA's fake vaccination program staged in 2011 to help find Osama bin Laden. On the 11th of September 2016, gunmen linked to the Pakistani Taliban shot Zakaullah Khan, a doctor administering polio vaccines, a reminder that the final cases may fall not to science but to trust.