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Reactions to a Second Dose of MMR Vaccine

The second dose was not associated with common adverse events.

In 1989, a second dose of the MMR vaccine was added to the recommended immunization schedule. As pediatric immunization schedules have grown in complexity, the public and media have focused increasingly on vaccine adverse events. To determine whether rates of adverse events after the second MMR dose differ from rates after the first dose, investigators compared rates of 13 parent-reported common adverse events occurring from 2 weeks before until 4 weeks after a first MMR dose (given to 535 infants aged 12 to 24 months) and a second dose (given to 633 children aged 4 to 6 years and to 632 children aged 10 to 12 years). Concomitant administration of other vaccines was common among the infants (89%) and younger children (81%), but not among the older children (<1%).

Rates of 3 of the 13 symptoms — fever, diarrhea, and rash — were significantly higher after the first dose than before the first dose; for example, fever incidence increased from 8% before, to 32% after, the first dose. For the second dose, symptom rates did not significantly increase after vaccination, regardless of age.

Comment: These reassuring results suggest that the second dose of the MMR vaccine is not associated with common adverse events. Unfortunately, it is impossible to know whether the increase in symptoms after the first dose was related to the MMR vaccine or to the concomitant administration of other vaccines.

— Howard Bauchner, MD

Published in Journal Watch General Medicine October 26, 2006

Citation(s):

LeBaron CW et al. Evaluation of potentially common adverse events associated with the first and second doses of measles-mumps-rubella vaccine. Pediatrics 2006 Oct; 118:1422-30.

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