The latest NHS figures for the COVER programme, which evaluates childhood vaccination in England, showed that three in ten children aged under five in the capital were yet to receive two vaccine shots against MMR as of September 2022.
Hackney had the lowest vaccination coverage, with 43 per cent of children not double jabbed against the disease.
This was followed by Kensington and Chelsea (41.5 per cent) and Camden (39.4 per cent).
Low vaccination rates for MMR lead to an increased risk of an outbreak of measles mumps or rubella (German measles), which could lead to serious illnesses including meningitis and pneumonia.
Polio was last year detected in sewage in London, though there have not been any confirmed cases since.
The NHS has warned that many children may have missed out on their routine vaccination appointments due to the Covid-19 pandemic, with parents urged to make an appointment with their GP as soon as possible.
Mr Khan said: “It’s concerning that vaccination rates for children have fallen since the pandemic. These vaccinations help to keep children safe and protected from serious illnesses such as mumps, measles and rubella (MMR) and polio, and that’s why I’m urging all parents to check that their children are fully up to date with routine immunisations as soon as possible.
“The NHS is also working closely with schools, GPs and community groups for their support in encouraging the take-up of immunisations, particularly among communities where vaccination levels are lower than average.”
London regional Chief Nurse Jane Clegg said: “It is really important that children are up to date with all vaccinations to maintain immunity.
“For example, since the MMR vaccine was introduced 35 years ago, cases of measles, mumps and rubella have become rare in the UK, and we haven’t seen a live case of polio since 1984”.