Question
Measles vaccine.
Answer
Measles vaccine is a live attenuated vaccine, given either as a monovalent vaccine or, more commonly, as part of the combination MMR vaccine (measles, mumps, rubella).
Schedule: first dose at 9–12 months of age (as a monovalent measles vaccine in many national programmes, given the higher risk of measles-related mortality in young children in endemic settings, and because MMR at this early age may show reduced seroconversion due to residual interfering maternal antibody), followed by a second dose later in childhood (either as monovalent measles vaccine or as MMR) to boost immunity and cover primary vaccine failure from the first dose.
Mechanism: as a live attenuated vaccine, it closely mimics natural infection, inducing robust, durable humoral and cell-mediated immunity, typically providing long-term (often lifelong) protection after the two-dose series.
Public health significance: measles is one of the most highly transmissible human infections (very high R0), requiring ~95% vaccination coverage to achieve herd immunity and interrupt sustained transmission; measles vaccination is a central pillar of global measles elimination programmes, and coverage gaps (even locally) can lead to outbreaks despite generally high national coverage.
Contraindications: pregnancy and significant immunosuppression, given the theoretical/actual risk from the live virus component.