Is the long-term immunity of the Measles, Mumps, and Rubella (MMR) vaccine affected by an additional dose given at 6 months?

From the Guidelines

No, an additional dose of the MMR vaccine given at 6 months does not negatively affect the long-term immunity provided by the standard MMR schedule. The standard MMR vaccination schedule includes doses at 12-15 months and 4-6 years of age, which provides long-lasting immunity against measles, mumps, and rubella 1. When an extra dose is given at 6 months (sometimes recommended during outbreaks or before international travel), it serves as supplemental protection but doesn't interfere with the development of long-term immunity from the regularly scheduled doses. This early dose is considered "extra" because infants under 12 months may not develop optimal immune responses due to the presence of maternal antibodies.

Key Points to Consider

• The American Academy of Pediatrics recommends that either MMR and varicella vaccines separately or the MMRV be used for the first dose of measles, mumps, rubella, and varicella vaccines administered at 12 through 47 months of age 1.
• For the first dose of measles, mumps, rubella, and varicella vaccines administered at ages 48 months and older, and for dose 2 at any age (15 months to 12 years), use of MMRV generally is preferred over separate injections of MMR and varicella vaccines 1.
• Parents should understand that if their child receives an early dose at 6 months, they will still need to complete the standard two-dose series starting at 12-15 months.
• The additional dose works by providing some immediate protection during a vulnerable period without compromising the robust and durable immunity that develops from the standard schedule.

Important Considerations for Vaccination

• The period of risk for febrile seizures is from 5 through 12 days after receipt of the vaccine(s) 1.
• No increased risk of febrile seizures is seen among patients 4 to 6 years of age receiving MMRV 1.
• Febrile seizures do not predispose to epilepsy or neurodevelopmental delays later in life and are not associated with long-term health impairment 1.

From the Research

Long-term Immunity of MMR Vaccine with Additional Dose at 6 Months

• The long-term immunity of the Measles, Mumps, and Rubella (MMR) vaccine given with an additional dose at 6 months is a topic of interest in vaccine research.
• A study published in 2024 2 found that children who received an early MMR vaccination between 6 and 12 months of age had a significant association between age of first MMR and MeV-specific neutralizing antibody levels later in life.
• However, the study also found that children vaccinated before 8·5 months of age exhibited a markedly faster antibody decay and lost their protective neutralizing antibody levels over 6 years.
• Another study from 2002 3 reported that a two-dose regime of measles vaccine is required to eliminate measles, and that a large proportion of pre-school children had measles and mumps IgG antibody below the putative level of protection after receiving a first dose of MMR vaccine.
• The study also found that after a second dose of MMR, the proportion negative to one or more antigens dropped to <4%.
• A study from 1994 4 compared long-term vaccination titres, early vaccination titres, and naturally acquired immunity to and booster effects on the measles virus, and found that vaccine-induced measles antibodies decline with time and may fall under the protective level.
• The study also found that children with naturally acquired immunity had significantly higher titres than children with vaccine-induced immunity titres.
• A study from 1986 5 analyzed the control of measles, mumps, and rubella by vaccination, and found that the use of a combined MMR vaccine has a number of logistical and financial advantages over immunization with separate vaccines.
• However, the study also found that certain vaccination programmes could actually increase the incidence of serious cases, such as congenital rubella syndrome (CRS), when vaccine coverage is low or the natural force of infection of rubella is high.
• A study from 1993 6 found that the duration of the immune response to MMR vaccine in children of two age-different groups did not differ, and that protective levels of antibodies against measles, mumps, and rubella viruses were found in all children 5 to 6 weeks after MMR vaccine administration.

Key Findings

• The long-term immunity of the MMR vaccine given with an additional dose at 6 months may be affected by the age of first vaccination and the number of doses received.
• Children vaccinated before 8·5 months of age may exhibit a faster antibody decay and lose their protective neutralizing antibody levels over time.
• A two-dose regime of measles vaccine is required to eliminate measles, and a second dose of MMR can significantly reduce the proportion of children negative to one or more antigens.
• Vaccine-induced measles antibodies decline with time and may fall under the protective level, while naturally acquired immunity provides higher titres.
• The use of a combined MMR vaccine has logistical and financial advantages, but certain vaccination programmes may increase the incidence of serious cases when vaccine coverage is low or the natural force of infection is high.