More than half the world’s countries will be at high or very high risk of measles outbreaks by the end of the year unless urgent preventative measures are taken, the World Health Organization warned on Tuesday.

Measles cases have been increasing across most regions mainly due to missed vaccinations during the COVID-19 years when health systems were overwhelmed and fell behind on routine vaccinations for preventable diseases.

“What we are worried about is this year, 2024, we’ve got these big gaps in our immunisation programmes and if we don’t fill them really quickly with the vaccine, measles will just jump into that gap,” the WHO’s Natasha Crowcroft, a Senior Technical Adviser on Measles and Rubella, told a Geneva press briefing.

“We can see, from data that’s produced with WHO data by the CDC (U.S. Centers for Disease Control and Prevention), that more than half of all the countries in the world are going to be at high or very high risk of outbreaks by the end of this year.”