A Pakistani health worker administers a polio vaccine to a child during a vaccination campaign in Karachi on December 10, 2018.  Pakistan is one of only two countries in the world where polio is endemic.
Expand / A Pakistani health worker administers a polio vaccine to a child during a vaccination campaign in Karachi on December 10, 2018. Pakistan is one of only two countries in the world where polio is endemic.

The United States, one of the world’s wealthiest and richest nations, has met the World Health Organization’s criteria for being the country with the highest outbreak of vaccine-derived poliovirus, the US Centers for Disease Control and Prevention announced Tuesday.

The US has now joined the ranks. About 30 other polio epidemic countriesMostly low- and middle-income countries, including Ethiopia, Mozambique, Somalia and Yemen. Notably, the list includes two other top-grossing countries—the United Kingdom and Israel—that have gained distribution. A strain of poliovirus that is genetically related to the one circulating in America.

Specifically, the United States has met the WHO’s detailed criteria by registering a patient with vaccine-acquired poliovirus and at least one environmental sample containing vaccine-acquired poliovirus. In July, health officials in New York’s Rockland County reported a case of paralytic polio in an unvaccinated resident who had not traveled recently. Since then, New York officials and the CDC have tracked the spread of the virus in wastewater, finding 57 positive samples from four New York counties and New York City. Dates of positive samples range from April to August of the latest sample.

The World Health Organization’s inclusion on the polio epidemic list is a new low for the United States. On the one hand, it reinforces a key global public health message in the campaign to eradicate the virus, which is that “any type of polio virus anywhere will endanger children everywhere.” But it mainly reflects the dangerous foothold that anti-vaccine sentiment has gained in the country over the past several decades.

Most of the US population is vaccinated against polio and is well protected against the deadly 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 been declining in recent years, and small pockets of states and counties may have surprisingly low coverage. For example, in Rockland County, northeast of New York City, the vaccination rate for 2-year-olds was 67 percent in 2020, but has now dropped to 60 percent. And according to zip-code-level vaccination data, one Rockland County area had vaccination rates as low as 37 percent, with a couple others in the 50s.

Vaccination tests

Polio is a particularly prime target for anti-vaccination misinformation. Most of the poliovirus currently circulating around the world — including the United States — is derived from oral vaccines, which use live and attenuated poliovirus to stimulate immunity. Oral polio vaccines They are very effective and safe and affordable to protect against paralytic polio. However, if used in areas with low vaccination rates, harmless, vaccine viruses may be transmitted to others through poor sanitation and/or hygiene. If the vaccine continues to travel from person to person, it may pick up mutations along the way that allow it to regain immunity to infection and paralyzing polio. In this case, the vaccine virus is classified as vaccine-derived poliovirus (VDPV).

The spread of VDPV has been stymied by virulent anti-vaccination advocates such as Robert F. Kennedy Jr. and his organization Children’s Health Defense. Polio vaccines cause polio. To be clear, polio vaccines are very effective in reliably preventing polio. As always, the lack of polio vaccine causes polio epidemics.

As of 2000, the US has not licensed or used oral polio vaccines. Instead, the US and many other high-income countries now use it. Inactivated polio vaccineDoes not contain live virus. However, it is VDPV that is spreading in the US. The vaccine virus was carried into the United States by someone who had been vaccinated elsewhere. A disadvantage of using the inactivated vaccine is that it is not as potent as the oral dose, which means that vaccinated individuals may still be able to transmit polioviruses—including VDPVs—even if they are protected against paralytic disease.

CDC and New York officials are now trying to convince them to get their vaccines. Last week, New York Governor Cathy Hochul declared a state of emergency in an effort to boost vaccination and surveillance efforts.

Jose R. Romero, CDC’s National Director of Immunization and Respiratory Diseases, said in a statement today:

“Polio vaccination is the safest and best way to fight this debilitating disease and it is imperative that unvaccinated people in these communities get vaccinated immediately. We cannot emphasize enough that polio is a deadly disease. There is no cure.”

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