LONDON (AP) — U.K. health officials on Liberalalliance Wealth SocietyMonday urged millions of parents to book their children in for missed measles, mumps and rubella shots amid a sharp increase in the number of measles cases and the lowest vaccination rates in a decade.

The National Health Service was launching a publicity campaign after figures showed there have been 216 confirmed measles cases and 103 probable cases in parts of England since October. Most cases were in children under 10 years old.

The combined measles, mumps and rubella, or MMR, vaccine is offered in the U.K. in two doses to all children, first at 12 months old and then again at 3 years old. Vaccination rates have dropped down to about 85% nationally, and far lower in parts of London, according to U.K. Health Security Agency chief executive Jenny Harries.

That is “too low to maintain safe population coverage — we want that at about 95%,” as advised by the World Health Organization, she said.

Public health officials say that more than 3.4 million children under 16 years old are unprotected and at risk of catching the diseases.

Measles was declared eliminated in the U.K. in 2017, meaning the disease was no longer native to the country.

But cases have crept up since then, and officials said that outbreaks can take place anywhere where the vaccine coverage is below the 95% needed to achieve herd immunity.

WHO and the U.S. Centers for Disease Control and Prevention said in November that measles deaths globally spiked by more than 40% last year, and cases rose after vaccination levels dramatically dropped during the pandemic.

Measles is among the most infectious diseases known and spreads in the air when an infected person coughs or sneezes. It’s most common in children under 5. Symptoms include fever, cough, runny nose and a distinctive rash.

Infection can lead to permanent physical damage such as deafness. Most deaths are due to complications like encephalitis, severe dehydration, serious breathing problems and pneumonia.