Polio, a disease once nearly eradicated worldwide, has recently made headlines, prompting public concern about its potential return. These reports, often stemming from detections in wastewater, have raised questions about the current state of this historically devastating virus. For decades, global efforts have successfully pushed polio to the brink of elimination. This article clarifies the current situation, explaining why the virus is being detected and its implications for communities globally.
Understanding Recent Polio Detections
Recent detections of poliovirus in wastewater, particularly in locations such as New York and London, have drawn significant attention. These findings often involve vaccine-derived poliovirus (VDPV) rather than wild poliovirus (WPV), which is nearing global eradication. In July 2022, a case of paralytic polio caused by VDPV type 2 was confirmed in an unvaccinated adult in Rockland County, New York, marking the first U.S. case since 2013. Subsequent wastewater surveillance in New York and London revealed genetically linked VDPV type 2, indicating community transmission.
Vaccine-derived poliovirus emerges in under-vaccinated populations when the live, weakened virus from the oral polio vaccine (OPV) circulates for an extended period. Over time, this weakened vaccine virus can genetically revert, regaining the ability to cause paralysis. While OPV is no longer routinely used in countries like the United States or the United Kingdom, it is still administered globally. Detections of VDPV in sewage highlight gaps in local vaccination coverage, allowing the virus to spread silently among susceptible individuals.
How Polio Spreads and Who Is at Risk
Poliovirus is highly contagious, primarily spreading through the fecal-oral route. This means the virus can transmit through contact with the stool of an infected person, contaminated food, or water. An infected individual, even without showing symptoms, can shed the virus in their feces for several weeks, silently spreading it within a community.
While most infected people remain asymptomatic or experience only mild, flu-like symptoms, a small percentage of unvaccinated individuals can develop severe complications. About one in 200 infections can lead to irreversible paralysis, typically in the legs. In rare cases, paralysis of breathing muscles can be fatal. The risk of developing polio or experiencing severe outcomes is almost exclusively limited to individuals who are unvaccinated or have not completed their full vaccination series.
The Critical Role of Polio Vaccination
Vaccination prevents polio and protects both individuals and communities. There are two primary types of polio vaccines: the inactivated poliovirus vaccine (IPV) and the oral poliovirus vaccine (OPV). IPV, administered as a shot, contains a killed poliovirus and is used in countries like the U.S. and the U.K.. This vaccine cannot cause polio and induces a strong immune response, protecting vaccinated individuals from paralytic disease.
OPV, given as oral drops, contains a live, weakened form of the virus. It is widely used in global eradication efforts because it protects vaccinated individuals and provides indirect immunity to others. While OPV carries a very rare risk of causing vaccine-derived poliovirus in under-vaccinated populations, its advantages in mass vaccination campaigns, such as low cost and ease of administration, make it invaluable in high-risk areas. Public health recommendations emphasize staying up-to-date on polio vaccinations to ensure robust protection against the disease.
Global Polio Eradication Status
The Global Polio Eradication Initiative (GPEI), launched in 1988, has reduced wild poliovirus cases by over 99% worldwide. This global partnership has prevented an estimated 20 million cases of paralysis in children. Of the three wild poliovirus types, type 2 was eradicated in 1999 and type 3 in 2020.
Despite this progress, wild poliovirus type 1 remains endemic in only two countries: Afghanistan and Pakistan. As long as wild poliovirus circulates anywhere, the threat of reintroduction exists globally, especially in vulnerable countries with weak health systems or through international travel. Gaps in global vaccination coverage allow both persistent wild poliovirus transmission and the emergence of vaccine-derived poliovirus, highlighting the need for sustained international efforts to achieve complete eradication.