The booster shot is supposed to provide extra protection for all children between the ages of one and nine, but the UKHSA stresses that the risk of infection is very small.
— For the vast majority, who are fully vaccinated, the risk of infection is low, but we know that areas of London where the polio virus has spread have some of the lowest vaccination rates, says Vanessa Saliba, epidemiologist at UKHSA.
Traces of poliovirus have been found in the sewage from eight boroughs of the British capital.
No new cases of polio have been confirmed in the UK, where polio was eradicated two decades ago.
Extensive global efforts in recent decades have come close to eradicating polio, a crippling and potentially fatal viral disease that mainly affects children.