Low polio vaccination rates and the presence of the virus in New York County’s wastewater suggest others are at risk after a young adult was paralyzed by polio this summer, the Centers for Disease Control and Prevention said Tuesday.
An unvaccinated person in Rockland County contracted polio in June — the second public outbreak of the virus in the United States in 43 years.
– We haven’t thought about polio for decades, aren’t we lucky? said Helen Jenkins, an infectious disease epidemiologist at Boston University School of Public Health, who was not involved in the New York case. “But now we’re thinking about it again, and if we can stop circulation everywhere, we can forget about it forever.”
Three doses of polio vaccine are more than 99% effective in preventing paralysis, but immunization rates for the virus in Rockland County much lower than the national figures.
According to the New York State Immunization Information System, CDC, 60.3% of children under 2 years of age living in Rockland County had received 3 doses of polio vaccine by August. Rates were 37.3% lower in at least one of the county’s 26 zip codes.
The polio vaccination rate across the country is approximately 93%.
The New York patient’s specific poly strain was present in wastewater from Rockland County and neighboring Orange County by May, suggesting “a continuing risk of community transmission and polio in unvaccinated individuals,” CDC researchers wrote.
Poliomyelitis infection is asymptomatic in most cases. However, according to the World Health Organization, 1 in 200 cases leads to paralysis. Paralysis can be fatal if the muscles used to control breathing are affected.
According to the CDC, the chance of paralysis is even lower at 1 in 1,900 among people infected with the strain identified in Rockland County. This suggests that there are many more asymptomatic cases that go undetected in the region.
“Even a single case of paralysis represents a public health emergency in the United States,” the researchers wrote.
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The last case of polio in the United States was in 1979, but the virus is still spreading in other parts of the world.
The Rockland County patient had not recently traveled outside the country, according to the CDC report. It is not clear where the patient contracted the disease, but he attended a large gathering eight days before the onset of symptoms – fever, constipation and abdominal pain.
Within three days, the patient also had a stiff neck and weakness in his legs. At first, the disease was mistaken for poliomyelitis and was thought to be acute mild myelitis caused by a different virus.
Stool samples, however, revealed 2 types of vaccine-derived poliovirus—a specific strain of the virus associated with the polio vaccine, which has not been used in the United States since 2000 but is still used in other parts of the world.
It is an orally administered vaccine that uses a live but weakened form of poliovirus to boost immunity. That virus can be shed in a person’s feces and, in rare cases, mutates into a form that can cause paralysis in an unvaccinated person. The injectable version of the vaccine used in the US does not and cannot use live virus.
So the Rockland County man may have been infected after someone who received the oral vaccine abroad returned to the U.S. and shed the weakened virus, the CDC wrote.
Polio has also been detected in sewage samples from New York City, but it is unclear whether it is linked to the Rockland and Orange County incidents.
Poliomyelitis is mainly transmitted through the fecal and oral route. This can often happen, for example, among young children who are learning to wash their hands properly.
Polio vaccines are considered stable and highly effective. The CDC recommends that children get four shots: 2 months, 4 months, 6 to 18 months, and then at age 5.
Three doses are sufficient to provide at least 99% protection, and a fourth dose is intended to maintain this protection for life. Some people may need extra boosters later if they travel to countries where polio is common or if they don’t get all the doses as children.
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