Mumps postexposure prophylaxis with a third dose of measles-mumps-rubella vaccine, Orange County, New York, USA.

Although the measles-mumps-rubella (MMR) vaccine is not recommended for mumps postexposure prophylaxis (PEP), data on its effectiveness are limited. During the 2009-2010 mumps outbreak in the northeastern United States, we assessed effectiveness of PEP with a third dose of MMR vaccine among contacts in Orthodox Jewish households who were given a third dose within 5 days of mumps onset in the household's index patient. We compared mumps attack rates between persons who received a third MMR dose during the first incubation period after onset in the index patient and 2-dose vaccinated persons who had not. Twenty-eight (11.7%) of 239 eligible household members received a third MMR dose as PEP. Mumps attack rates were 0% among third-dose recipients versus 5.2% among 2-dose recipients without PEP (p=0.57). Although a third MMR dose administered as PEP did not have a significant effect, it may offer some benefits in specific outbreak contexts.