An excerpt from Your Immune System: The Amazing Science of Who You Are.
Polio is a viral disease of the nervous system. It attacks people of all ages, but children and young adults are disproportionately affected. Like many other viral diseases, polio starts with nonspecific symptoms, like headache, fever, sore throat, vomiting, and diarrhea. These symptoms occur as the patient’s innate immune system responds to the viral PAMPs, the pathogen-associated molecular patterns described in chapter 2, and as the adaptive immune response begins. Although most people resolve the infection, in a minority of individuals, the disease progresses. The most feared complication of polio is paralysis, typically of the legs, but in some the paralysis is more widespread, even making breathing difficult when the respiratory muscles are involved.
Interestingly, unlike many other infectious diseases that appeared to wane as sanitation and nutrition improved, the experience with polio was different. Infantile paralysis, as the disease was also known, was first described by Michael Underwood, a British physician with expertise in childhood illnesses, in 1789. While cases of the disease were not rare, it was not considered a major public health concern until the end of the nineteenth and beginning of the twentieth century, when epidemics began to emerge in Europe and the United States. The explanation is reminiscent of the reasoning behind the hygiene hypothesis, described in chapter 7. Many medical microbiologists believed that, before improvements in living conditions came along, the polio virus was common in the environment, so much so that mothers typically experienced low-level infections during their childhood and developed antibodies against the virus. These antibodies were transferred through the placenta, and later through breastmilk, to their babies, providing protection against the virus, and making natural infections less severe. These minor natural infections resulted in active immunization, which protected individuals from more serious disease later in life.
With the advent of a cleaner environment, the theory goes, mothers were more rarely infected and therefore did not make high levels of antibody to transfer to their babies. This was a perfect setup for epidemics. Children were at risk of infection, and because polio is easily transmissible, infected children could also infect others. The ensuing epidemics in the twentieth century made polio one of the most feared diseases throughout Europe and the United States. Outbreaks were more frequent in the summertime, a more permissive time of year for the virus to flourish, and in many communities, public parks and pools were closed. Outdoor life came nearly to a halt as children were kept home for their safety, disrupting life for many families. There was enormous public interest in a solution to this problem. Scientists were on the hunt for a means to produce a safe and effective vaccine.
Real physician voices, twice a week
Free, and one click to unsubscribe.
The road to a vaccine could not begin, however, before the virus that causes polio was isolated and studied. This first step was accomplished in 1908 at the University of Vienna, with the work of Karl Landsteiner, a scientist best known for identifying the major blood types (A, B, AB, and O), which made blood transfusions safe, a finding that earned Landsteiner a share in the 1930 Nobel Prize. After Landsteiner’s discovery of the virus, another essential step in the search for a vaccine was accomplished decades later when, in 1949, John Enders, a virologist; Thomas Weller, a microbiologist; and Frederick Robbins, a physician, teamed up in Boston to learn how to grow the poliovirus in the laboratory. This breakthrough made it possible to purify and attenuate the virus so that a vaccine could be imagined. For their work, the three investigators earned the Nobel Prize in Medicine in 1954.
With the virus in hand, scientists considered several approaches to produce a vaccine. Some thought using a live but weakened virus might be best, ensuring that all the components of the virus would be intact and thereby stimulate a robust immune response. Worried that the risk of infection would be too high even if the virus were weakened significantly, Jonas Salk, working at the University of Pittsburgh, studied ways to kill the virus while still retaining its ability to induce an immune response. To do his work, Salk had substantial financial support, including from the National Foundation for Infantile Paralysis, which was started in 1938 by President Franklin Roosevelt, himself a victim of polio-induced paralytic disease.
Roosevelt’s March of Dimes campaign contributed millions to the development of the vaccine. People nationwide had collection bottles for their dimes in their kitchens to support the campaign. The public was so engaged with the vaccine effort that, when a vaccine was ready to be tested, more than a million children, who earned the moniker “polio pioneers,” participated in a clinical trial for safety and effectiveness. The study showed outstanding results, and the vaccine was approved for general use in 1955. As cases of polio plummeted, Salk became an American folk hero. Today, there are two types of polio vaccines: one, a killed-virus vaccine based on Salk’s work that is injected; and the second, a living but attenuated viral vaccine, developed by Albert Sabin working in Cincinnati, that is given orally. Polio has now become rare in many parts of the world. Indeed, it is on the World Health Organization’s list of diseases that could and should be eradicated from the globe. Unfortunately, because uptake of the vaccine is not universal, pockets of infection remain, and the dream of a polio-free world has yet to be achieved.
Gary A. Koretzky is a physician-scientist.
