US officially added to WHO list of countries affected by poliovirus outbreak

The United States, one of the wealthiest and most developed countries in the world, has met the World Health Organization’s criteria to be on the list of countries with circulating vaccine-derived poliovirus, announced the US Centers for Disease Control and Prevention on Tuesday.

The United States now joins the ranks of approximately 30 other countries affected by the polio epidemic, mostly low- and middle-income, including Ethiopia, Mozambique, Somalia and Yemen. Notably, the list includes only two other high-income countries – the UK and Israel – that have detected the circulation of a poliovirus strain genetically linked to the one spreading in the United States.

Specifically, the United States has met the criteria for the WHO list by documenting a patient with vaccine-derived poliovirus and having at least one environmental sample of vaccine-derived poliovirus. In July, Rockland County health officials in New York reported a case of paralytic polio in an unvaccinated resident who had not traveled recently. Since then, New York officials and the CDC have been monitoring the spread of the virus in sewage, finding 57 positive samples from four New York counties and New York City. Dates of positive samples range from April to recent sampling in August.

Inclusion on the WHO list of polio outbreaks is a new low point for the United States. On the one hand, it reinforces a key global public health message in the campaign to completely eradicate this virus, which is that “any form of poliovirus anywhere is a threat to children everywhere.” But it mostly shines a light on the dangerous entrenchment that anti-vaccine sentiment has gained in the country over the past few decades.

The vast majority of the American population is vaccinated against poliomyelitis and well protected against this dangerous disease. The CDC recommends that children receive three doses of the inactivated polio vaccine at 24 months, followed by a fourth dose between ages 4 and 6. But vaccination rates have dropped in recent years, and small pockets of states and counties may have incredibly low coverage. For example, in Rockland County, just northeast of New York, the vaccination rate for 2-year-olds was 67% in 2020, but has slipped to 60% now. And according to ZIP code-level vaccination data, one area in Rockland County has a vaccination rate as low as 37%, with a few others in the 50s.

Vaccination challenges

Polio is a particularly big target for anti-vaccine misinformation. Much of the poliovirus currently circulating in the world today, including the United States, is derived from oral vaccines, which use live and weakened polioviruses to boost immunity. Oral polio vaccines are highly effective in protecting against paralytic polio and are safe and affordable. But, if used in areas with low vaccination rates, harmless and immunizing vaccine viruses can spread to others due to poor sanitation and/or hygiene. If the vaccine continues to move from person to person, it may pick up mutations along the way that allow it to regain the ability to cause infection and paralytic polio. At this point, the vaccine virus is reclassified as vaccine-derived poliovirus (VDPV).

The circulation of VDPV has been gobbled up by dangerous anti-vaccine advocates, such as Robert F. Kennedy Jr. and his organization, Children’s Health Defense, who giddily tout the false claim that polio vaccines cause polio. To be clear, polio vaccines are very effective in preventing polio safely. As always, lack of polio vaccination causes polio outbreaks.

The United States has not licensed or used oral polio vaccines since 2000. Instead, the United States and many other high-income countries now use an inactivated polio vaccine, which does not contain live virus. Nevertheless, a VDPV is what is spreading in the United States. The vaccine virus was likely brought to the United States by someone vaccinated elsewhere. The disadvantage of using an inactivated vaccine is that it is not as potent as oral doses, which means that vaccinated people can still spread poliovirus, including VDPVs, despite being highly protected against paralytic disease.

CDC and New York officials are now trying to convince vaccine holders to get vaccinated. Last week, New York Governor Kathy Hochul declared a state of emergency in an effort to bolster vaccination and surveillance efforts.

In a statement today, José R. Romero, director of the CDC’s National Center for Immunization and Respiratory Diseases, insisted that:

“Vaccination against polio is the safest and best way to combat this debilitating disease and it is imperative that members of these communities who are unvaccinated learn about polio vaccination immediately. We can’t say enough. insist that polio is a dangerous disease for which there is no cure.”