New York, Aug 12 (IANS): There must be several hundred cases of undiagnosed polio circulating in the US, according to a senior official with the Centres for Disease Control and Prevention (CDC).

This follows the news of an unvaccinated man paralysed by the virus in New York, last month, a first in nearly a decade in the country. The last known case was in 2013.

The New York case is "just the very, very tip of the iceberg" and an indication there "must be several hundred cases in the community circulating", Dr. Jose Romero, director of the CDC's National Centre for Immunisation and Respiratory Diseases, was quoted as saying to CNN.

"There are a number of individuals in the community that have been infected with poliovirus. They are shedding the virus," he said. "The spread is always a possibility because the spread is going to be silent."

Polio is a very contagious viral disease. About 3 in 4 people infected with polio don't have symptoms, but they're still capable of spreading the virus to others, according to the CDC.

Only a relatively small number, about 1 in 200 infected people, become paralysed. A few of those who are paralysed die because they can't breathe.

"There isn't just one case of polio if you see a paralytic case. The incidence of paralytic polio is less than 1 per cent," Dr Patricia Schnabel Ruppert, health commissioner for Rockland County, was quoted as saying to BBC.

"Most cases are asymptomatic or mildly symptomatic, and those symptoms are often missed. So there are hundreds, perhaps even thousands of cases that have occurred in order for us to see a paralytic case."

Meanwhile, UK health officials are set to offer a targeted inactivated polio vaccine (IPV) booster dose to all children between the ages of 1 and 9 to limit the spread of the virus' outbreak in London.

This follows the discovery of Type 2 vaccine-derived poliovirus in sewage in north and east London.

According to the UK Health Security Agency, 116 samples of vaccine-like poliovirus have been detected in the sewage water in London between February and July 2022.