On Oct. 21, 2009, Merck announced that the company will not resume production of monovalent measles, mumps, and rubella vaccines.

The combination vaccine M-M-R ®II was recommended by the ACIP, the American Academy of Pediatrics (AAP), and the American Academy of Family Physicians (AAFP), and was preferred over the monovalent vaccines because it eliminated the need for 3 separate injections and reduced the chance of delays in helping protect against any of these potentially serious diseases.

In 2008, Merck stopped making the 3 monovalent vaccines due to manufacturing constraints and had announced plans to resume production only if sufficient manufacturing resources were available to do so without compromising supplies of M-M-R.