Should infants get their first MMR vaccine later than 12 months?

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vaccinationThe U.S. Advisory Committee on Immunization Practices recommends giving infants the first measles vaccine between ages 12 and 15 months, and then following that with a booster between the ages of 4 and 6 years. However, a new study suggests that getting the first shot at 15 months may provide longer lasting protection than one received at 12 months. Researchers say that while these data are impressive, there is not yet enough evidence to warrant changes in recommendations.

Dr. Gaston De Serres of the Quebec National Institute for Public Health in Quebec City and colleagues conducted a case-control study, using 102 measles cases and 510 vaccinated controls. They looked at data from all cases of measles in the province between Jan 1 and December 31, 2011 in children ages 5 to 17 who had received two doses of the MMR vaccine beginning at 12 months or older. Controls, who had also received two doses of MMR beginning at 12 months or older, were selected from the provincial vaccination registry. Researchers reported that 90 percent of the cases and about 5 percent of the controls received the first dose of MMR at 12 or 13 months. Only about 5 percent of cases and 20 percent of controls got the first dose at 15 months or later. Using these data, researchers reported that receiving the first dose of the vaccine at 12 or 13 months was associated with a 6 fold increased risk of getting the measles.

Although these figures are highly significant, the study did have several limitations. First, it was a retrospective study: cause and effect conclusions cannot be made. Second, the study subjects received the first and second doses much closer to each other than is common practice in the United States, meaning this study cannot be used to inform changes in recommendations here. And last, the majority of the study subjects mothers had had the measles, meaning they were highly likely to have passed antibodies on to their children, thus making them less likely to be affected by early vaccination than those children whose mothers have not had the disease.