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Happy Birthday to the ‘Greatest Public Health Experiment in History’

The Salk polio vaccine goes to trial in a Pittsburg elementary school.

At its mid-1900s peak, the polio virus typically made its move during the warm summer months, spreading mostly via feces, but sometimes spit and snot. It was known as a disease of children, like the measles or mumps, and it infected whole towns at a time. Ninety percent of those infected wind up with zero symptoms, another few percent will experience mild, general symptoms of viral infection, and the rest will suffer lifelong disability or death.

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The polio worst-case is rare as a percentage, but the pre-vaccine omnipresence of the infection—epidemics were common, especially in the first-world—made paralytic polio not so much a rarity. It was a terrifying everyday reality, a public health crisis with a brutal signature of deformity and death. In 1952, there were 21,000 paralytic cases.

The historian William O'Neil wrote that, "Paralytic poliomyelitis (its formal name) was, if not the most serious, easily the most frightening public health problem of the postwar era." Every year the situation seemed to get worse, and paralytic polio eventually became the number one killer of children among communicable diseases.

The virus mostly haunts the digestive system, multiplying in the intestines and, later, the bloodstream and lymph nodes. In around one percent of cases, it makes the jump into the nervous system, spreading via nervous fibers into the meninges tissues surrounding the brain and, possibly, into the brain itself. This advanced progression is usually considered to be dumb luck and, unlike the neutrotropic rabies virus, entering the brain offers the poliovirus no particular advantage.

In the brain and spinal cord, the poliovirus targets motor neurons in particular. As your heart and lungs happen to be controlled by muscles (or are muscles), poliomyelitis, the proper name for a polio infection, quickly becomes something much more dire. This is paralytic polio; death is one possibility, but more likely is paralysis, which takes hold anywhere from two to 10 days after the first minor symptoms develop. In some cases, the damage is permanent, leaving patients with muscular deformations and occasionally quadriplegia, which is more or less paralysis of everything from the neck down. Think iron lungs.

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The reason for the first-world emphasis is thought to be over-sanitation, which keeps infants from being exposed to the virus at an age where they could quickly defeat the virus and grow up with poliovirus antibodies. So: the virus hits later in life, without the benefit of maternal immuno-protection. It's a pretty interesting idea, though unsettled.

The vaccine research push in the 1940s and 50s makes recent anti-Ebola efforts look pale by comparison, as a quick PubMed search reveals. And the eventual success of that push made Jonas Salk, the developer of the final, successful vaccine, a celebrity almost overnight.

As a virologist, Salk was interested in the flu, to the point of engaging in unethical research involving patients in a Michigan mental institution. After spending years in underfunded, cramped university laboratories, Salk accepted an offer from the National Foundation for Infantile Paralysis (NFIP) to work on polio. In exchange, he got a big lab with new equipment and a research dream team, and the promise that after he finished his poliovirus classification work, he could use the facilities and staff for his influenza research. In 1955, poliovirus vaccine funding from the NFIP had reached $67 million annually.

Salk took an alternative, more conservative approach to vaccines, using a dead version of the virus rather than the live versions that had been mostly favored until the mid-1950s. "Everything scientists believed about polio at first was wrong, leading them down many blind alleys," O'Neil wrote. "Furthermore, most researchers were experimenting with highly dangerous 'live' vaccines. In one test, six children were killed and three left crippled."

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The combination of crushing public health crisis and dangerous experimentation was not a good look, and Salk wanted something that could go public as soon as possible. Using the safer "killed" version of the virus seemed like the only option.

In 1954, Salk was testing his vaccine on children, and, in a classic PR move, he included his wife and three children in the tests. The first mass inoculation took place on February 23 of that year in Pittsburgh at the Arsenal Elementary School. In March, just weeks later, the New York Times offered this reporting:

This was described as the long-sought answer to a vital question, making it practically certain not only that the vaccine will produce effective immunity against all three types of polio but also that the immunity will be of the lasting type, possibly for the individual's lifetime.

This could mean that within the next three to five years polio, crippler of young and old alike, will join diphtheria, smallpox, typhoid and other formerly dreaded infectious diseases as plagues finally tamed and conquered by man.

By 1954, his vaccine was ready for very large-scale field trials.

Those trials were unlike anything else in history. It was, "the most elaborate program of its kind," O'Neil wrote, "involving 20,000 physicians and public health officers, 64,000 school personnel, and 220,000 volunteers." 1,800,000 schoolchildren participated.

Two years later, the vaccine was declared safe and ready for public dissemination, offering the potential of near 100 percent protection. The Salk vaccine was quickly translated into mass-reproducible form, and Salk spent the next several years basking in the public glow: medals, parades, movies, declarations. He was a virologist war hero.

The question answered by Salk was deeper than polio. It was about the immune system in general. Would the body, one exposed to a dead/killed virus, develop not just antibodies to that one specific version of the virus by all versions? What sort of memory does the body have? The conclusion, Salk reported after the Arsenal trial, was this, per the Times:

That by the proper use of a suitably prepared non-infectious [dead] virus vaccine, antibody [immunity] can be induced readily in amounts equal to that resulting from natural infection [by live viruses]: And, that, in many instances, concentration of antibody in the blood stream can be raised to levels beyond that which may be regarded as an average response to the naturally acquired infection.

Salk continued, adding that, "the immunologic mechanism is altered by primary immunization [with killed non-infectious viruses] in a manner similar to that observed in persons who have had a natural infection." And, finally, "these effects can be achieved with small doses of vaccine and with few injections."

Poliovirus has been considered to be eradicated in most of the developed world since 1994. Its current resurgence in war-torn Syria and portions of Africa was listed as a world health emergency by the WHO in 2014.