Who Created The Polio Vaccine?

August 10, 2020

In the early 1950s, two prominent medical researchers each found a way to protect the world from polio, a paralyzing disease commonly referred to as poliomyelitis. Dr. Jonas Salk and Dr. Albert Sabin developed a vaccine that nearly eradicated polio worldwide. Here’s how they did it.

What is polio?
Poliomyelitis is a disease caused by three variants of the poliovirus, according to a 2012 review written by microbiologist and polio expert Anda Bykus and published in the World Journal of Virology. The virus, which only infects humans, can damage neurons that control movement, leading to partial or complete paralysis. According to the U.S. Centers for Disease Control and Prevention (CDC), people can contract the virus by eating contaminated food or water, or by allowing contaminated objects (such as dirty hands) to touch or enter their mouths.

Studies of Egyptian mummies have shown that polio affected children at least as far back as ancient times, but the United States did not experience its first polio epidemic until the late 19th century. In the United States in 1916, more than 27,000 people were paralyzed by the disease and at least 6,000 people died from it, according to History.com. Over the next few decades, the epidemic expanded throughout the United States and Europe. In 1952 alone, there were 58,000 new cases of polio in the United States and 3,000 deaths from the disease.

As medical experts learned more about the virus, they discovered that it could infect people without causing symptoms. In a 1947 study published in the American Journal of Hygiene, researchers reported that an epidemic of poliovirus in New York City sewage meant that, at the time, for every symptomatic or paralyzed case of polio, there were an estimated 100 asymptomatic cases. Today, more recent studies suggest that 72 of the 100 people infected with the virus will never develop symptoms, and about 1 in 4 infected people will experience only flu-like symptoms that last 2 to 5 days before going on their own, according to the CDC.

In the late 1930s, researchers learned that infected people shed the virus in their feces for a few weeks if they had symptoms of the disease. Researchers later confirmed that people who were infected but asymptomatic could still shed the virus, making them sick. According to the CDC, people who do get sick can shed the virus immediately before symptoms appear and for up to 2 weeks after symptoms appear.

Development of the Salk vaccine
Researchers began working on a polio vaccine in the 1930s, but early attempts were unsuccessful. No effective vaccine was available until 1953, when Jonas Salk introduced his inactivated polio vaccine (IPV).

According to History.com, Salk studied the virus as a student at New York University in the 1930s and helped develop an influenza vaccine during World War II. in 1948, he received a research grant from President Franklin D. Roosevelt’s National Foundation for Infantile Paralysis (later named the March of Dimes). Roosevelt had contracted polio at the age of 39 in 1921, a disease that left him permanently paralyzed in both legs, and in 1938, five years into his presidency, Roosevelt helped create the National Foundation for Infantile Paralysis to raise funds and provide assistance to polio-endemic areas.

Thanks to the work of previous researchers, Salk was able to grow the poliovirus in monkey kidney cells. He then isolated the virus and inactivated it with formalin, an organic solution of formaldehyde and water that is commonly used as a disinfectant and antiseptic. A similar procedure was tested several years earlier, in 1935, by American scientist Maurice Brody, who extracted poliovirus from the spinal cord tissue of live monkeys and suspended the virus in a 10 percent solution of formalin, writes polio expert Bakers. Brody tested his vaccine first on 20 monkeys and then on 300 schoolchildren, but the results were so poor that Brody did not test it any further.

Salk’s vaccine was unusual in that instead of using a weakened version of a live virus, such as those used to treat mumps and measles, Salk’s vaccine used a “killed” or inactivated version of the virus. When the “dead” poliovirus is injected into the bloodstream, it cannot cause infection because the virus is inactive; however, the immune system cannot distinguish between activated and inactivated viruses, and it produces antibodies to fight the virus. These antibodies persist and protect a person from contracting the poliovirus in the future.

In 1953, Salk began testing his inactivated polio vaccine (IPV) on a handful of former polio victims in the Pittsburgh area, as well as himself, his wife, and their three sons. The initial results were promising, according to History.com, and on March 25, 1953, he announced his success on the CBS National Broadcasting Network. He became an instant celebrity.

The first large-scale clinical trial of the Salk vaccine began in 1954 with more than one million participants. It was the first vaccine trial to implement a double-blind, placebo-controlled design – now a standard requirement for modern vaccine research, according to Arnold S. Monto’s 1999 review published in the journal Epidemiological Reviews.

The scientist who led the vaccine trial, Dr. Thomas Francis Jr. from the University of Michigan, announced the positive results at a press conference on April 12, 1955. Later that same day, the U.S. government declared Salk’s vaccine safe and effective for use, according to the Philadelphia College of Physicians’ “History of Vaccines.

After the press conference, CBS reporter Edward R. Murrow asked Salk, whose vaccine it was.” Well, the people, I would say, “Salk famously replied.” No patent. Can you patent the sun?” Salk never patented his vaccine.

Just a few weeks later, reports began to surface of children receiving the vaccine after experiencing paralysis. According to the CDC, more than 250 new cases of polio were traced back to batches of vaccine produced by Cutter Laboratories. These batches had contained live, active strains of poliovirus.

The U.S. Surgeon General halted the administration of all polio vaccines until all manufacturers could be investigated and their safety verified. At the time, there was very little government oversight of vaccine manufacturers, but that quickly changed after what is now known as the “Carter incident.” Since that time, not a single case of polio has been attributed to the Sabin vaccine.

Sabin’s oral polio vaccine
While Salk was developing an inactivated polio vaccine, his professional competitor, Dr. Albert Sabin, a virologist at the University of Cincinnati, was developing a vaccine made with an active but attenuated virus. Sabin opposed Salk’s vaccine design, arguing that vaccines for inactivated viruses were dangerous.

By 1963, Sabin had created an oral live virus vaccine for all three types of poliovirus that was approved for use by the U.S. government.In 1972, Sabin donated his strain of the vaccine to the World Health Organization (WHO), greatly increasing the availability of the vaccine in low-income countries.

Sabin’s oral polio vaccine (OPV) is vital to help reduce the number of polio cases worldwide, but unlike the Salk vaccine – which has no risk of paralysis – the risk of OPV causing paralysis is minimal. Today, WHO estimates that approximately 1 in 2.7 million doses of OPV causes paralytic polio.

Since 2000, Salk’s inactivated polio vaccine has been the only version available in the United States to avoid the risk of any OPV-related vaccine-induced polio. OPV is still used in many parts of the world, but the WHO’s Global Polio Eradication Initiative aims to stop using OPV completely once wild (non-vaccine related) polio is completely eradicated.

The CDC now recommends that children receive four doses of IPV, one each at 2 months, 4 months, 6 to 18 months, and 4 to 6 years of age. Thanks to the widespread use of the polio vaccine, the United States has been polio-free since 1979. According to WHO, the number of polio cases caused by wild poliovirus has decreased by 99% globally since 1988, from about 350,000 cases per year to only 33 new cases in 2018.