By Sonam Lhamo
In the late 1940s and early 1950s, polio was a feared infectious disease in the U.S. During summers, when the disease peaked, parents would keep their children from going to swimming pools and movies for fear of their children contracting polio from infected children1. Polio is a highly contagious, infectious disease caused by polioviruses and is transmitted by ingesting contaminated water and food2,3. After entering the human body through the gastrointestinal tract, polioviruses enter cells lining the intestine and the tonsils using a specific receptor (CD155) found in those tissues and starts to make lots of copies of itself. The virus then enters the blood stream and can spread to other organs. In the majority of cases, polio causes a mild sore throat, fever, nausea, and stomach pain. However, in 1 in 200 infected people, the virus enters the nervous system and destroys nerve cells that control movement, causing permanent paralysis of muscles of the leg or diaphragm-making it hard to breathe without the aid of a respirator. Polio kills 10-15% of those who develop paralysis. Paralysis caused by poliovirus is known as poliomyelitis and is used interchangeably with polio.
Polio affects mainly children because of their poor handwashing and hygiene. In 1952, almost 60,000 children were infected with polioviruses. Tens of thousands became paralyzed, and 3,000 died1. Hospitals were set up with huge tank respirators called iron lung machines to keep paralyzed children breathing and alive. It was common to see children who had been paralyzed by polio walking around with crutches. Polio spread widely in clusters through local contaminated water and became a public crisis in the 1940s and 1950s. However, today, polio is eradicated in all but two of the affected countries. So, how was such a global feat achieved?
Two major types of polio vaccines rolled out in large clinical trials in the mid-1950s and early 1960s4. The first major polio vaccine, known as the Salk vaccine, was developed by Jonas Salk, a doctor and scientist at the University of Pittsburgh in Pennsylvania. The Salk vaccine used inactivated, or killed, polioviruses developed by growing wild polioviruses on monkey kidney cells and inactivating the viruses with formalin5. The vaccine was designed to be protective against all three serotypes of polioviruses. Salk was one of the pioneers working on inactivated virus vaccines. At the time, traditional vaccines used live, weakened viruses4.
Salk’s research on the polio vaccine was funded by the National Foundation for Infantile Paralysis (NFIP), a non-profit organization created by former president Franklin D. Roosevelt to support polio research and help polio patients. Roosevelt himself had paralytic poliomyelitis and appealed to the public for funds for polio vaccine research. During a fundraising campaign for polio vaccine research known as the March of Dimes, Americans sent in millions of dimes and thousands of dollars to the White House6.
The Salk vaccine trial started in 1954 and included 2 million children across the United States, Canada, and Finland. The double-blinded clinical trial involved 650,000 children receiving the polio vaccine or placebo injection and 1.2 million children who received no injection (observed control)7. A year later, in 1955, the vaccine was approved with 90% effectiveness in preventing paralytic poliomyelitis. The government then advocated to make the Salk vaccine free to the public and within a year, 30 million American children received the vaccine, causing cases of polio to rapidly decline to half the cases seen in the 1950s. Moreover, cases of paralytic poliomyelitis dropped from 15,000 in 1950s to 100 in 19618.
In the late 1950s, another major polio vaccine called the Sabin vaccine was ready for clinical trials4. The Sabin vaccine contains live, attenuated polioviruses given in oral drops or sugar cubes and was developed by Albert Sabin, a professor of pediatric research at the University of Cincinnati in Ohio. However, because the Salk vaccine was already approved and being used in the U.S., there was not a lot of support for conducting the Sabin vaccine trial in the U.S. Instead, the Sabin vaccine trial took place in South America and the Soviet Union. The vaccine was approved by the Soviet Union in 1961 and was soon adopted by the World Health Organization (WHO). Because of the ease of orally administrating the Sabin vaccine (also known as the oral poliovirus vaccine or OPV), the WHO replaced the Salk vaccine with the OPV for vaccinating children around the world. Moreover, since the Sabin vaccine is given orally, the virus from the vaccine sheds in feces and therefore seemed to offer immunity to even unvaccinated individuals. However, since the Sabin vaccine virus is live, it occasionally mutates enough to become pathogenic and cause poliomyelitis. Thankfully, this mutation is rare (1 in 3 million OPV doses between 1990-1999)9. Because Salk’s inactivated vaccine (also known as inactivated poliovirus vaccine or IPV) does not pose the same threat, the U.S. replaced the oral poliovirus vaccine with the inactivated poliovirus vaccine in 20009. However, OPV is still widely used today in the developing world due to ease in its administration.
In 1979, almost 15 years after the approval of the Salk vaccine, polio was declared eradicated in the U.S. Moreover, global polio cases had dropped from 350,000 cases across 125 countries in 1988 to just 143 cases in two countries in 201910. The large success of polio vaccination is due to several key factors.
First, there was great public support for the polio vaccine research in the 1940s due to widespread campaigns. Moreover, the debilitating paralysis caused by polio made the search for a vaccine urgent.
Second, both the OPV and IPV are highly effective in reducing polio symptoms and disease. On top of that, since polioviruses are known to naturally infect only humans; there is no risk of the virus lurking in animals or other reservoirs and suddenly emerging again to cause widespread polio.
Third, a highly effective vaccine is only one part of eradicating infectious diseases. Manufacturing and distributing vaccines to the community and ensuring that people get the vaccine are equally important. To that end, the Global Polio Eradication Initiative (GPEI), founded in 1988, initiated global polio vaccine immunization with the goal of immunizing at least 80% of the population to eradicate polio11.
So far, around 2.5 billion children have received either the OPV or the IPV, which is given in a 3 or 4 dose series to children before they reach the age of five. A three-dose series of the IPV is almost 100% effective against polio.
Despite the widespread eradication of polio, it is still endemic in two countries, Pakistan, and Afghanistan, where tens to hundreds of cases are reported each year12. Political conflicts and distrust of Western countries have thwarted efforts to vaccinate against polio in these regions. For instance, in the aftermath of the September 11, 2001, attacks, the United States’ war on terrorism in Afghanistan and Pakistan intensified distrust between the U.S. and the two countries, resulting in a major blow to the poliovirus vaccination effort.
Once a major public crisis gripping America in the early 20th century causing devastating life-long paralysis, polio is now almost eradicated, thanks to the development of poliovirus vaccine and the global effort of vaccinating children. We have come a long way since the major polio outbreaks. Despite the huge success in eradicating polio in almost every country, we still have work to do in the few remaining countries where polio remains endemic. Unless polio transmission is stopped in these countries, all countries remain at risk of polio.
Today, can we eradicate an infectious disease for the second time in history? To eradicate polio or any disease that has effective vaccines, countries must find ways to come together in honesty to successfully prevent disease.
Polio is a highly contagious disease that can cause life-long paralysis and was one of the worst outbreaks in the U.S. history. With the successful development of poliovirus vaccines and the global vaccination initiative, polio has been eradicated in all countries except two.
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2. What is polio? (2020, June 17). https://www.cdc.gov/polio/what-is-polio/index.htm
3. Polio. (2002, January 17). https://en.wikipedia.org/wiki/Polio
4. Jonas Salk and Albert Bruce Sabin. (2021, June 15). Science History Institute. https://www.sciencehistory.org/historical-profile/jonas-salk-and-albert-bruce-sabin
5. Baicus, A. (2012). History of polio vaccination. World Journal of Virology, 1(4), 108. https://doi.org/10.5501/wjv.v1.i4.108
6. History.com Editors. (2009, November 16). Franklin Roosevelt founds march of dimes. HISTORY. https://www.history.com/this-day-in-history/franklin-roosevelt-founds-march-of-dimes
7. Juhl, R. P. (2020, September 16). Lessons from how the polio vaccine went from the lab to the public that Americans can learn from today. The Conversation. https://theconversation.com/lessons-from-how-the-polio-vaccine-went-from-the-lab-to-the-public-that-americans-can-learn-from-today-145604
8. What is polio? (2020, June 17). https://www.cdc.gov/polio/what-is-polio/index.htm
9. Why do we still use Sabin poliovirus vaccine? (2017, October 1). virology blog. https://www.virology.ws/2015/09/10/why-do-we-still-use-sabin-poliovirus-vaccine/
10. The U.S. government and global polio efforts. (2021, October 29). KFF. https://www.kff.org/global-health-policy/fact-sheet/the-u-s-government-and-global-polio-efforts/
11. (n.d.). GPEI-Homepage. https://polioeradication.org/
12. Beenish Javed. (2020, September 19). Why polio continues to be a health risk in Pakistan. DW.COM. https://www.dw.com/en/why-polio-continues-to-be-a-health-risk-in-pakistan/a-54934680