Question
MMR vaccine.
Answer
MMR vaccine is a combination live attenuated vaccine protecting against Measles, Mumps, and Rubella — three important viral childhood diseases, each capable of causing significant morbidity (and, for rubella, congenital malformation if acquired by a pregnant woman).
Composition: contains live attenuated strains of measles virus, mumps virus, and rubella virus, each individually weakened through serial passage to reduce virulence while retaining sufficient immunogenicity to induce protective immunity.
Schedule: typically given as a first dose at 9–15 months of age (varies by national schedule) and a second dose later in childhood (e.g., around 15–18 months to 4–6 years) to boost immunity and cover the small proportion of children who fail to seroconvert after the first dose (primary vaccine failure).
Mechanism: as a live attenuated vaccine, it replicates transiently within the host, closely mimicking natural infection and inducing both strong humoral and cell-mediated immunity, typically providing durable, often lifelong protection after the two-dose series.
Contraindications: pregnancy (theoretical risk to the fetus from the live rubella component, though no confirmed teratogenic cases have been documented from inadvertent vaccination — nonetheless, pregnancy should be avoided for a defined interval after vaccination, and the vaccine should not be given to a known pregnant woman) and significant immunosuppression (risk of disseminated infection from the live virus components).
Key public health significance:
- Prevention of congenital rubella syndrome — vaccinating children (and ensuring susceptible women of childbearing age are immune) prevents rubella infection during pregnancy, avoiding the severe congenital malformations (cardiac defects, cataracts, deafness) caused by transplacental rubella infection in the first trimester.
- Measles elimination programmes — MMR (or measles-containing vaccines) are central to global measles elimination efforts, given measles’ very high transmissibility (high R0) requiring very high (~95%) vaccination coverage for herd immunity.
- The vaccine has been the subject of a now thoroughly discredited and retracted claim linking it to autism — extensive subsequent research has found no such association, and the original study was found to be fraudulent.