The acting director of the CDC, Jim O'Neill, in an X post on Monday called on vaccine manufacturers to develop three separate monovalent vaccines to replace the combined measles-mumps-rubella vaccine.

This comes hours after O'Neill signed off on a vaccine advisory panel's recommendation against the use of a combined measles-mumps-rubella-varicella vaccine before the age of 4 years.

Instead, shots will be given for measles-mumps-rubella with a separate vaccine for varicella, commonly known as chickenpox.

According to the U.S. Food and Drug Administration's website there are currently no monovalent measles, mumps or rubella vaccines licensed for use in the United States.