Salk, Sabin and a century of research into the polio vaccine

The polio vaccine is used to prevent infection with a virus that can affect the spinal cord and brain, leading to paralysis. Before the introduction of the vaccine in the 1950s, the disease crippled approximately 35,000 people each year, according to the Centers for Disease Control (CDC). Thanks to the work of Salk, Sabin and other researchers, by 1979 the United States was polio-free, but the virus still ravages parts of the Middle East and Africa, where vaccination efforts are ongoing.

The first polio epidemic and early prevention efforts

Though there is some indication of a similar, if not the same, paralytic disease in ancient Egypt and other cultures, the first major documented outbreak of polio in the United States occurred in Rutland County, Vermont, in 1894. The disease resulted in 18 deaths and 132 cases of permanent paralysis, but researchers did not determine that the disease was caused by an infectious agent until 1905, after major epidemics in Sweden. It was three more years before the agent was identified as a virus by researchers in Vienna. Early prevention pamphlets issued by health departments stressed cleanliness and hygiene. It is now known that the virus is transmitted via feces-contaminated food and water, and potentially by flies that come into contact with infected feces, according to the Global Polio Eradication Initiative.

The first polio vaccine trials

In 1910, Dr. Simon Flexner at the Rockefeller Institute for Medical Research in New York discovered neutralizing antibodies against poliovirus in the blood of monkeys that had survived polio. His proof-of-concept work was one of the first steps toward creating a vaccine against the virus. The first vaccines against polio were tested in 1935, but the various trials were disastrous, leading to death and paralysis among test subjects. A researcher at Lederle Laboratories, Dr. Hilary Koprowski, had a better outcome in 1948, but his vaccine was only tested on himself and his assistant. He moved on to the first human trials in 1950, inoculating disabled children with his attenuated oral vaccine. They developed antibodies, indicating the success of the vaccine, but his methods were controversial.

In 1949, poliovirus was found to be present as three types, complicating vaccine development, as any feasible polio vaccine would need to immunize against all three types. That same year, Dr. John Enders’ research team in Boston cultured poliovirus for the first time in non-nervous tissue, a step that would lead to the Nobel Prize in Physiology or Medicine in 1954 and open the door to researchers previously hindered in investigating the virus.

Salk and the inactivated polio vaccine

Major breakthroughs in the development of the polio vaccine came with the work of Dr. Jonas Salk, who was funded by the National Foundation for Infantile Paralysis, which is now known as the March of Dimes. On Mar. 26, 1953, Salk announced on national radio that he had successfully created a vaccine against polio. Though Salk’s early human trials followed the controversial methods of Koprowski, his announcement led to the approval of field trials in the U.S., which started in Apr. 1954. A total of 1.3 million children participated in the randomized trial of Salk’s “killed” virus vaccine, which was licensed a year later with a protection rate against disease of 60 to 70 percent, according to A Science Odyssey. However, some production runs of the vaccine contained insufficiently killed virus, leading to some cases of disease and paralysis and suspension of the vaccination program.

Sabin and the attenuated oral vaccine

As Salk gained fame with the first licensed vaccine, Dr. Albert Sabin worked with the Russian government to develop an oral vaccine that offers longer immunity against the virus. His live-attenuated vaccine used a weakened form of the virus that could be added to sugar cubes, making it easier to vaccinate children. By 1959, Sabin was conducting clinical trials in 10 million children, leading to the licensing of the first oral polio vaccine, which protected against type 1 poliovirus, in 1960. Vaccines against the other types followed, and by 1963 a combined oral vaccine protected against all three types of poliovirus. By 1968, Salk’s inactivated vaccine was phased out in favor of Sabin’s oral vaccine. However, the attenuated virus could gain strength and become infective again, causing researchers to continue work on improving the vaccine.

The modern polio vaccine

In 1997, an improved version of Salk’s inactivated vaccine was phased in again, and by 2000 the United States had transitioned away completely from use of live virus in the polio vaccine. However, due to its ease of use, Sabin’s oral vaccine is still used in eradication efforts in polio hotspots in the Eastern Hemisphere. For information about when and how you should be vaccinated against polio, visit the CDC’s website.

For more highlights of the history of the development of the polio vaccine, visit the interactive timeline offered by The College of Physicians of Philadelphia.