Children aged 1 to 9 in London will be offered a polio vaccine booster after a poliovirus was detected in sewage.
Sampling found type 2 vaccine-derived poliovirus collected from the Beckton sewage treatment works, with positive samples also found in sewage in north and east London.
The targeted inactivated polio vaccine (IPV) booster dose will be offered across all London boroughs to help reduce further spread of the virus and ensure a high level of protection from paralysis.
The programme will start with the areas affected and where vaccination rates are low before being rolled out across all boroughs.
Dr Vanessa Saliba, consultant epidemiologist at the UK Health Security Agency, said: 'No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low. But we know the areas in London where the poliovirus is being transmitted have some of the lowest vaccination rates. This is why the virus is spreading in these communities and puts those residents not fully vaccinated at greater risk.
'Polio is a serious infection that can cause paralysis but nationally the overall risk is considered low because most people are protected by vaccination. The last case of polio in the UK was in 1984, but decades ago before we introduced the polio vaccination programme around 8,000 people would develop paralysis every year.'
Eight sites across London are currently being sampled, with a further 15 sites to be started mid-August. A further 10 to 15 sites outside of London will be stood up nationally to see if poliovirus is spreading outside the capital.