In 1988, the World Health Organization resolved to eradicate poliomyelitis; polio for short. This followed the confirmation that the last case of smallpox was diagnosed in October 1977 and the WHO declared smallpox to be eradicated in 1980. This was done through a worldwide vaccination program and is the only human infectious disease to be considered eradicated. Like smallpox, polio was spread in repeated epidemics, terrifying parents who feared that their children would get the disease. So, 34 years later where are we in the process? Now, a recent case of polio in New York has caught the headlines. Buffeting along as we come off COVID and hear news of monkeypox, it is reasonable to be concerned and ask, “What’s next? Is polio coming back?”
Polio is caused by the poliovirus that is spread by the fecal-oral route, meaning that the virus is ingested by consuming contaminated food or water. It has developed the ability to resist acid in the stomach. Once in the intestines, it enters host cells in the lining of the intestinal wall. There, like all viruses, it transforms the host cell into a factory producing more virus. These are then shed from the body in feces to be spread to other people. Unlike other viruses that we have discussed recently, polio did not originate in another animal and then jump species to humans. It likely originated in humans because we are its only host. It has been with us for thousands of years as suggested by ancient art that depicts people with classic shriveled deformity of limbs.
Similar to COVID, 70% of people who become infected have little or no symptoms, while another 25% have a sore throat and fever. Incubation time from exposure to onset of symptoms is 3-6 days. The illness lasts about 2 weeks, however, a person continues to shed active virus for up to 6 weeks after resolution of the illness.
In about 1% of cases, the infection spreads to the nervous system damaging nerve cells in the brain and spinal cord that go to muscles and control muscle function. We refer to this as "spinal polio". This is most likely to occur in children under the age of five, but can occur at any age. Even though it is more likely to get into nerves in children, the amount of nerve damage is usually less severe. Only 1 child in 1,000 who come down with “spinal polio” end up with paralysis and it usually only involves one leg. While nerve involvement is much less common in adults, the outcome can be much more debilitating when it does occur. One in 75 adults with “spinal polio” will have paralysis that involves multiple limbs and can also affect the muscles of breathing. When the diaphragm is paralyzed, the person will die if assistance is not given to help them breath. The “iron lung” was one such machine used in the past to help a person with polio breath.
When children develop polio paralysis of a limb, the muscles waste away and do not grow as the rest of the body develops. This leads to a deformed limb that is classic for polio. If the leg is involved, it may not be capable of supporting weight. Leg braces and crutches may be needed to allow the person to walk. In the 1940’s and 50’s, the rate of disabling poliomyelitis in the US was about 15,000 cases of paralysis per year. This jumped to about 35,000 cases per year during outbreaks.
There are three reasons that polio is still with us. The first is the lack of good public health in many developing countries to maintain effective vaccination programs. The second has to do with the vaccine itself and the third has to do with politics around the vaccine. The vaccine is commonly given as a drop of liquid in the mouth. This vaccine is an actual form of the virus that has been chemically altered so that it causes only a very mild infection. This is called a “live-attenuated” vaccine. Recall that all vaccines work by simulating an infection so that the immune system mounts a response by making antibodies that give immunity if an actual infection occurs. Because the vaccine is active virus, all be it attenuated, there is a small chance that it can cause the disease it is designed to prevent. The goal is to create herd immunity to the level that poliovirus would be eradicated from the herd. This strategy works very well. In 1988, when the WHO began its vaccination campaign, there were 350,000 reported cases of polio. In just a few years into the campaign, that number dropped to about 1,000 per year. Currently, the number is down to less than 100 per year worldwide. Some of these cases are vaccine induced, while others are occurring in areas lacking vaccination.
The cases of non-vaccine related polio, referred to as wild polio, have been centered in Nigeria, Pakistan and Afghanistan. The problem is one of trust. Nigeria was a British colony that came to resent Western medicine being imposed on them and started off with a mistrust of the West. With the US invasion of Afghanistan and Iraq, a rumor began to spread around Muslim countries that vaccination was a CIA plot to sterilize Muslims. This was not helped when it became public knowledge that, in 2011, the CIA conducted a fake hepatitis vaccination program in which blood samples were taken from Pakistani children with the hope of using genetic testing to track down Osama bin Laden. The blow-back from this has resulted in at least 60 international healthcare workers being murdered due to suspicion that they were working for the CIA. It also added further fuel to the rumors that vaccines are a CIA plot. Muslin clerics also opposed vaccination on the grounds that one step in the manufacturing involves an enzyme derived from pigs. When the WHO learned of this concern, the manufacture was changed to remove the enzyme from the preparation after the step that requires the enzyme. Testing is then done to confirm that no detectable enzyme is present in the purified, final product. No polio vaccine currently being manufactured contains any pork related substances.
Fortunately, things are improving. The Taliban in Afghanistan announced in October that they will allow polio vaccination by outside humanitarian aid organizations, however, will not provide the vaccinations through the government. In Pakistan, a new Prime Minister has recently been elected who supports polio vaccination and has meet with the Bill Gates as well as representatives from Rotary International and pledged his support. Both the Bill Gates Foundation and Rotary International have had long standing programs to support the eradication of polio through vaccination. In 2003, Nigerian clerics and government officials called for a boycott of the vaccine out of fear that it was laced with anti-fertility drugs and could cause cancer. This eventually led the WHO to declare that “Nigeria is the most significant generator of polio in the world”. In 2016, the Nigerian government reversed its stance due to a significant rise in new polio cases over the preceding 10 years. They allowed UNICEF workers to do a widespread polio vaccination program in their country. Because of the decade long boycott, Nigerian parents remained reluctant to accept the vaccine for their children, but this is slowly changing as personal stories of polio induced paralysis in children and adults have circulated.
Prior to the new case in New York, which resulted in paralysis in a young, unvaccinated male adult, there had not been a case of wild polio originating in the US since 1979. There had been sporadic other cases that were all in travelers coming to the US, and the last case like that was in 2013. Public health officials have used the relatively new technique of testing wastewater and have detected polio in sewage in many areas around the state, including New York City. While about 80% of people are vaccinated against polio, there are some communities where the rate is as low as 50%, well below the threshold where herd immunity might be protective.
As long as we still have areas with naturally occurring polio virus, we will not be able to eradicate the disease. This means that we will need to continue vaccination with a vaccine that will cause an occasional case of polio. If wild polio was eradicated, then we could eventually stop vaccinating against it and the vaccine induced cases would also go away. Since we are seeing an average of 100 cases per year of polio worldwide, then one case in New York does not seem to ring an alarm. However, if enough parents decide to avoid vaccinating their children, then we may well return to what we saw during the era of the iron lung.
Corrections: This article contains corrections from the original published version around the governments of Pakistan, Afghanistan and Nigeria attitudes towards vaccination.