All children aged one to nine in Brent will be offered a polio booster vaccine after the virus was found in 116 sewage samples across London.

Vaccine-derived poliovirus has been detected in sewage in Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.

There have been no confirmed cases yet but the decision has been made that a targeted inactivated polio vaccine (IPV) booster dose should be offered to all children aged one to nine.

In June people were urged to keep their vaccines up to date after polio was detected in sewers across north and east London.

Nationally the overall risk of paralytic polio is considered low because most people are protected from this by vaccination.

Across London, childhood vaccination uptake is lower than the rest of the country.

Following initial findings at Beckton sewage treatment works earlier this year, 116 type 2 poliovirus (PV2) isolates were identified in 19 sewage London samples collected between February 8 and July 5.

Most are vaccine-like virus and only a few have sufficient mutations to be classified as vaccine derived poliovirus (VDPV2). VDPV2 is of greater concern as it behaves more like naturally occurring "wild" polio and may, on rare occasions, lead to cases of paralysis in unvaccinated individuals.

Dr Vanessa Saliba, consultant epidemiologist at 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.

"It is vital parents ensure their children are fully vaccinated for their age.

"Following JCVI advice all children aged one to nine years in London need to have a dose of polio vaccine now – whether it’s an extra booster dose or just to catch up with their routine vaccinations. It will ensure a high level of protection from paralysis. This may also help stop the virus spreading further."

Cllr Ketan Sheth, chair of NW London Joint Health Scrutiny Committee, said: "The news that the polio virus has been found in sewage is very worrying.

"I am pleased that the NHS has acted quickly and is offering children aged one to nine an urgent booster vaccination.

"Parents and carers will be contacted by their GP shortly and it is very important that they attend the appointment and protect their child from serious illness."

The NHS will be contacting parents of eligible children aged one to nine.