A polio virus particle.Credit:AP
The agency said it had not located anyone infected with the virus and that the risk to the wider population was low. The decision to offer young children boosters was a precaution,it said.
“This will ensure a high level of protection from paralysis and help reduce further spread,” the agency said.
In rare cases,the live virus contained in the oral polio vaccine used in the global effort to eradicate the disease can mutate into new forms potent enough to trigger new outbreaks. The vaccination booster effort in London will use injected polio vaccines that do not carry that risk.
The agency said it is also expanding surveillance of sewage water to at least another 25 sites in London and nationally.
Most people across Britain are vaccinated against polio in childhood. According to the World Health Organisation,only one in 200 polio infections leads to paralysis;most people don’t show any symptoms.
“If[polio] continues to spread,it will result in cases of paralysis.”
Nicholas Grassly,professor of vaccine epidemiology at Imperial College London
The Health Security Agency said it was working closely with health authorities at the WHO and in the United States and Israel to investigate any links to polio viruses detected in those two countries.