The<unk>  is a mixture of 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 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.
MMR vaccine
Polio vaccine
Childhood vaccination schedule
BCG vaccine
Ebola vaccines
Influenza vaccine
Influenza vaccine 
COVID-19 vaccines