Rubella virus neutralizing antibody response after a third dose of measles-mumps-rubella vaccine in young adults.

•Rubella immune response after receipt of a third dose of MMR vaccine was evaluated.•Rubella antibody titers were 4.5 times higher after vaccination in young adults.•3% had low titers 1 month postvaccination; 24% had low titers 1 year postvaccination.•Young adults with low rubella titers are more likely to benefit from a third dose.