The deadly poliovirus may have been circulating in New York city since April and elsewhere in the state for up to one year, suggests a new analysis of wastewater sample from there.
The study from the US Centers for Disease Control and Prevention (CDC) published on Tuesday sheds more light on the polio case detected in an unvaccinated person in New York last month even as the virus was known to be eliminated from the US around 40 years ago.
In June, a young adult resident of a New York suburb was hospitalised after experiencing fever, neck stiffness, gastrointestinal symptoms as well as limb weakness, and was found to carry the pathogen.
The virus was then isolated from the person and also identified in wastewater samples in two neighbouring New York counties.
CDC experts said the person did not travel internationally during the period when they were exposed to the pathogen and may have caught the virus through local transmission.
Researchers found the strain the person was exposed to was linked to a weakened form of the virus used in the oral polio vaccine known as Vaccine-derived poliovirus type 2.
Since the US stopped oral polio vaccination in 2000, the original transmission of this strain may have emerged from someone outside the country.
Based on virus genome analysis, the strain behind the New York case was linked to vaccine-related polioviruses recently detected in wastewater in Israel and the UK.
Researchers warned that such infections can emerge when live, attenuated oral polio vaccine is administered in a community with low vaccination coverage.
Such live, attenuated vaccines are made from a laboratory-weakened form of virus that can stimulate a strong immune response without causing disease
CDC experts warned that unvaccinated people in the US remain at risk for paralytic poliomyelitis – a severe form of infection with the virus that causes paralysis – if they are exposed to either wild or vaccine-derived poliovirus.