Healthcare professionals and parents are being urged to vaccinate against MMR as London experiences an outbreak of measles.
There have been more than 60 cases of measles in the last two months in London – with 48 of the cases being in people aged 15 and over.
Public Health England (PHE) said it would normally expect fewer than ten cases during the same period.
A spokesman said all of the patients had not been vaccinated against measles.
PHE’s regional director for London Dr Yvonne Doyle said the outbreak was mainly in adolescents and young adults and said it was never too late for them to have the vaccine.
She said anyone who is unsure if they had two doses of the vaccine in the past should speak to their GP.
“There’s no harm in receiving an additional dose where there is any uncertainty,” she said.
The outbreak comes as PHE marked European Immunisation Week by called for parents and healthcare professionals nationally to help eradicate measles.
In the last 12 months there have been 1,206 cases of measles in the UK.
PHE’s head of immunisation Dr Mary Ramsay said there was “an opportunity to make measles history”.
More than 90% of children in the UK are receiving the first dose of the measles vaccine by the age of two, with coverage of the second dose at 88%, said PHE.
The combined measles, mumps and rubella (MMR) vaccine was introduced in 1988.
It is routinely given to children from 12 months of age, with a second dose at three years and four months.
PHE said adolescents and young people are now mostly affected and the immunisation gap was partly due to controversy about the vaccination in the late 1990s.
PHE said a 3.5% increase of the MMR vaccine – about 24,000 children a year – is all that is needed in England to close the immunisation gap and reach the World Health Organization’s 95% uptake target for two-year-olds.
Ramsay said: “To help us close this gap, we want professionals to ensure they make every contact count to spread awareness and provide information on vaccinations to parents and young adults.”
Parents should also think about older children and adolescents getting vaccinated if they missed out.