The urgent campaign comes after vaccine-derived poliovirus was detected in sewage samples from eight of the capital’s 32 boroughs.
No cases have yet been diagnosed but the virus’s presence in sewage suggests it is being transmitted in the UK for the first time in 40 years.
The extra jabs will be offered to 900,000 children. Parents will be contacted by their GPs.
Health Secretary Steve Barclay said: “I recognise parents and guardians will be concerned.”
“However, I want to reassure people that nobody has been diagnosed with the virus and the risk to the wider population is low.”
The UK Health Security Agency (UKHSA) detected the virus 116 times in 19 London sewage samples.
It was found in Barnet, Brent, Camden, Enfield, Waltham Forest, Hackney, Haringey and Islington.
Fears were first raised in June after tests at Beckton sewage treatment works, in east London.
The inactivated polio vaccine protects against symptoms such as paralysis that can occur in the most severe cases.
The outbreak is thought to originate from someone entering the UK after having an older type, the oral polio vaccine.
If jab rates are low, the virus can then spread and mutate into the more dangerous vaccine-derived polio. Jab coverage in London is only 87 percent.
UKHSA consultant epidemiologist Dr Vanessa Saliba said: “It is vital parents ensure their children are fully vaccinated for their age.”
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