Health officials in California are concerned about the confluence of the coronavirus and flu in the upcoming months, noting a substantial decline in child vaccination rates since the pandemic.

Dr. Mark Ghaly, California’s health and human services secretary, said Tuesday that the number of children vaccinated for measles, mumps and rubella as they prepare to enter elementary school plummeted when schools and businesses closed in the spring.

He says the flu usually stresses hospitals, and they are also now grappling with coronavirus cases, including in some children.

California is dealing with a surge in coronavirus cases but has recently seen signs the spread could be slowing.