Our clinic has been giving measles, mumps, rubella vaccine (MMR) by the wrong route (intramuscular rather than subcutaneous) for years. Should these doses be repeated?

All live injected vaccines (MMR, varicella, and yellow fever) are recommended to be given subcutaneously (Subcut). In February 2023, FDA approved the administration of MMRII (Merck) brand of MMR by either Subcut or IM routes. The Priorix (GSK) brand of MMR is approved only for Subcut administration. Intramuscular (IM) administration of any of these live virus vaccines is not likely to decrease immunogenicity, and doses given IM do not need to be repeated. When administering MMRII by the IM route, select an appropriate needle length for the patient’s size. See Immunize.org’s clinical resource “Administering Vaccines: Dose, Route, Site, and Needle Size” at www.immunize.org/catg.d/p3085.pdf.