The MMR vaccine is a mixture of three live attenuated viruses, administered via injection for immunization against measles, mumps and rubella. It is generally administered to children around the age of one year, with a booster dose before starting school (i.e. age 4/5). In the United States, the vaccine was licensed in 1963 and the booster began in the mid 1990s. It is widely used around the world; since introduction of its earliest versions in the 1970s, over 500 million doses have been used in over 60 countries. As with all vaccinations, long-term effects and efficacy are subject to continuing study. The vaccine is sold by Merck as M-M-R II, GlaxoSmithKline Biologicals as Priorix, and sanofi pasteur as TRIMOVAX.