All children aged one to nine living in London will be offered a polio booster vaccine following the detection of the virus in sewage.
The UK Health Security Agency has confirmed that since early February, the virus was found 116 times across 19 sewage samples collected in the capital.
“Polio is a serious infection that can cause paralysis but nationally the overall risk is considered low”
At least one positive sample of the poliovirus is currently present in Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest and there are signs of some level of virus transmission between London boroughs, it added.
However, the government agency said there has been no confirmed cases of polio and that the risk to the wider population is low.
Most of the viruses identified are a weakened “vaccine-like” strain, but there are concerns about the discovery of “a few” which have mutated into “vaccine-derived” strains which can on rare occasions lead to paralysis in unvaccinated individuals.
Following the discovery of the vaccine-derived virus, the Joint Committee on Vaccination and Immunisation (JVCI) has advised that a targeted inactivated polio vaccine (IPC) booster dose should be offered to all children between the ages of one and nine, in all London boroughs.
This aims to help to provide a high level of protection from paralysis and reduce further spread of the virus.
The programme will begin with areas where the virus has been detected and where vaccination rates are low, followed by a “rapid rollout” across the rest of the capital.
Chief nurse for the NHS in London Jane Clegg said the health service would “shortly” be contacting parents of eligible children to “offer them a top-up dose to ensure they have maximum protection from the virus”.
She added that parents and carers of children who are not up to date with their routine vaccinations were already being reached out to for catch-up appointments.
Dr Vanessa Saliba, consultant epidemiologist at UKHSA, 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.”
She added: “Polio is a serious infection that can cause paralysis but nationally the overall risk is considered low because most people are protected by vaccination.”
Dr Saliba highlighted that the last case of polio in the UK was in 1984. But she added that “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,” she added.
“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.”
Health and social care secretary Steve Barclay added: “Vaccines offer the best defence to children, and those around them, so I would encourage families to ensure they are up to date with their routine jabs, and to come forward for the polio booster as soon as they are contacted by the NHS.”