GENEVA -- The UN health agency is warning that more than 117 million children in more than three dozen countries could miss out on measles vaccines as countries suspend immunizations and other services to fight the coronavirus outbreak.

The World Health Organization says 24 countries have already postponed measles vaccination campaigns to avert further spread of COVID-19 disease, and another 13 are expected to do so by the end of the year.

"If the difficult choice to pause vaccination is made due to the spread of COVID-19, we urge leaders to intensify efforts to track unvaccinated children, so that the most vulnerable populations can be provided with measles vaccines as soon as it becomes possible to do so," WHO said in a statement Tuesday.

WHO and partners say they support a "pause of mass campaigns" in their measles and Rubella initiative to protect communities and health workers, but "this should not mean that children permanently miss out."