London could see a measles outbreak with tens of thousands of cases because of low levels of vaccination, health chiefs have warned.

Estimates show between 40,000 and 160,000 cases could occur in the capital unless vaccination rates improve, according to the UK Health Security Agency (UKHSA).

The risk in London is thought to be because of low vaccination rates over several years, further worsened by the Covid-19 pandemic.

The UKHSA said there had been 128 cases of measles between January and June 2023, compared with 54 cases across 2022 – with 66% of cases detected in London.

Parents are being urged to check their children are up to date with their measles, mumps and rubella vaccines (MMR) or call their GP practice if unsure.

Those going abroad for summer holidays are also being asked to catch up on any missed vaccinations.

Dr Vanessa Saliba, UKHSA consultant epidemiologist, said: “Measles can be a serious infection that can lead to complications, especially in young children and those with weakened immune systems.

“Due to longstanding suboptimal vaccine uptake there is now a very real risk of seeing big outbreaks in London.”

She added: “Nobody wants to see their child or loved ones sick with measles, or put others who are more vulnerable, like babies, at risk.

“I urge those who have missed their MMR vaccines to catch up now.”

The UKHSA said that young people aged 19 to 25 are likely to be most susceptible to the outbreak as they may have been affected by unfounded stories in the early 2000s about the links between MMR jabs and autism.

The World Health Organisation estimates 95% of the population need to be vaccinated to prevent an outbreak.

But in England, around 85% of the population aged five and above is fully vaccinated.

Around 10% of children in the country are left unprotected from measles by the time they are ready to start school, with the rate in London at about 20%, the UKHSA said.

Measles is contagious but is easily preventable with vaccination, which comes in two doses.

Children in the UK can have a first dose of the MMR vaccine on or after their first birthday and the second dose by the time they are three-and-a-half years old.

Jane Clegg, regional chief nurse for the NHS in London, said: “Cases of measles in the capital remain low but it’s really important that people check that they, and their children, are up to date with their jabs and protected against MMR – and if you have any questions or concerns, please get in touch with your GP practice or local pharmacist for advice.

“Now’s the time to act to protect yourself and loved ones from measles.”

Commenting on the warning, Dr David Elliman, consultant in community child health at Great Ormond Street Hospital, said the “announcement that London could experience a large outbreak is no surprise”.

He said: “Uptake of all routine vaccines in London has always been lower than most of the rest of the UK, as a whole, and within London are pockets of very low uptake.

“It is in these areas that the danger of outbreaks is greatest.”

He also said that as well as teenagers and young adults, infants under 12 months are also at the greatest risk of measles as they are not offered the MMR vaccine at that age.

Dr Elliman said: “About one in 1,000 to one in 3,000 people who contract measles will die.

“If UKHSA projections are correct, we could see dozens of deaths in London.

“This assumes that nothing changes.

“The intention is to take action to ensure that this does not happen.”