Briefly last week there were headlines about a small number of polio cases found in the Philippines, a country declared polio free in 2000. While a few cases in another country may not seem very alarming, these cases starkly reflect a global public health failure. Polio is a very contagious viral infection that is usually acquired orally. Infected individuals shed the virus in their feces for weeks which can contaminate their immediate environment, as well as water sources. Poliovirus can survive for at least a few weeks on surfaces and in soil and water. Infection can result when contaminated water is ingested or virus is picked up on the hands and introduced into the mouth, eyes or nose. New cases typically come from close contact with infected individuals or from contaminated water sources. Fortunately, there are no animal reservoirs for human poliovirus and only humans carry the disease. Consequently, if we could eliminate the virus from all living humans then within a few months all the virus in the environment would lose infectivity and this disease would disappear permanently (as happened for smallpox). While there is no cure for polio infection, we’ve had extremely effective vaccines for over 50 years that can prevent infection and spread. The combination of no non-human reservoirs and the availability of effective vaccines makes polio eradication an achievable goal, one which the World Health Organization (WHO) predicted would be accomplished by the year 2000. Yet here we are in 2019 with polio still problematic.
Failure to eradicate polio is more of a social/political issue than a medical one. The remaining major poliovirus positive countries are Pakistan, Afghanistan, and Nigeria. These countries are beset with problems such as poverty, geographic isolation, war, unstable governments, and anti-vaccine bias that hinder delivery of vaccines to their population. Until vaccine coverage is more universal in these countries, they will remain infectious hotspots that not only continue to have internal polio cases, but also put the entire world at risk. Since air travel can move infected individuals quickly around the world, all countries must maintain polio vaccine vigilance to prevent reintroduction of the virus into countries where there is no longer endemic poliovirus. Unfortunately, keeping levels of polio immunization high in countries that haven’t had polio in decades can be challenging. The Philippine government has embarked on a new poliovirus vaccine campaign to try to thwart any further spread. Hopefully they can regain their polio-free status soon, but it’s a good lesson for other countries about not letting vaccination levels decrease until the poliovirus endgame is complete and we are finally rid of this disease forever.