Health officials found polio virus in New York City’s sewage, the city’s Department of Health and Mental Hygiene announced Friday. That means polio is likely circulating in the city undetected.
The virus was previously found in wastewater samples from Orange County and Rockland County, north of New York City, in May, June and July. Last month, a case of paralyzed polio was diagnosed in an unvaccinated adult in Rockland County.
“The risk to New Yorkers is real, but the defense is so simple — get vaccinated against polio,” said New York Health Commissioner Dr. Ashwin Vasan in a statement.
The Centers for Disease Control and Prevention recommends a series of three-dose vaccinations in early childhood, plus a booster dose between 4 and 6 years of age.
Most people get those injections as part of their routine childhood vaccinations. In New York City, about 86% of children ages 6 months to 5 years have received all three doses. Statewide, 79% of New Yorkers have received three or more doses by age 2.
But polio vaccination rates are much lower in Orange and Rockland counties, at around 60% in children under 2 years of age.
New York State Health Commissioner Dr. Mary Bassett said the discovery of polio in New York City’s sewage was “alarming, but not surprising.”
“For every identified case of paralytic polio, hundreds more may go undetected,” Bassett said in a statement.
The Rockland County patient was infected with polio from a vaccine, a strain linked to a live, attenuated virus used in an oral polio vaccine that is no longer administered in the U.S.
A person who takes the oral polio vaccine can shed short-lived virus, so if a community has low vaccination coverage, the virus can then spread. If it circulates widely enough, it can mutate to become more virulent.
“We need to monitor sewerage to find out exactly how extensive it is,” said Vincent Racaniello, a professor of microbiology and immunology at Columbia University. “I suspect that in the big cities where people from countries where they use the infectious vaccine, you would find it in the sewers.”
Polio is highly contagious, but about 72% of infected people have no visible symptoms, According to the CDC. Another 25% may develop flu-like symptoms that disappear within a few days. Polio rarely causes permanent paralysis of the arms and legs. It can also lead to meningitis (swelling of the brain and the membranes of the spinal cord) or paresthesia (the feeling of pins and needles in the legs).
The CDC estimates that between 2% and 10% of cases of paralytic polio in children are fatal. In adolescents and adults, the mortality rate is higher: 15% to 30%.