Measles risk elevated with earlier first vaccine dose

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1. Children given their first of two measles vaccines at 15 months of age or older had a significantly lower risk of measles infection during a recent epidemic than those given their first dose at 12 or 13 months.

2. Timing of the second dose of measles vaccine did not significantly affect risk of contracting measles.

Evidence Rating Level: 3 (Average)

Study Rundown: The timing and number of live attenuated measles vaccine doses recommended for infants and children has evolved since measles vaccine was first developed in the 1950s. Since 1970, Canadian health officials have recommended the first dose of vaccine at 12 months and since 1996 a second dose.  Despite widespread vaccine uptake an epidemic of measles occurred in the Quebec province in 2011. Initial studies conducted at the outbreak school showed an increased risk for measles infection in children vaccinated at 12 months compared to those vaccinated at 15 months or later. This study took a broader look at the entire Quebec province during this epidemic to examine the risk of measles and timing of measles vaccination. Cases of children with measles infection during the outbreak were matched to controls from the same schools who did not contract measles. Children who received their first measles vaccine at 12 or 13 months old had a risk of measles 5.2 times higher than those that received their first vaccine at 15 months or greater. The timing of the second dose did not confer any difference in risk. There was minimal variability in timing of vaccination among study participants, which limited the study from identifying an ideal time of vaccination. This study provides strong evidence that the vaccine schedules in Canada could be adjusted to provide better protection against measles.

Click to read the study in Pediatrics

Relevant Reading: Largest measles epidemic in North America in a decade- Quebec, Canada, 2011: contribution fo susceptibility, serendipity, and superspreading events.

In-Depth [case-control study]: 102 case and 510 control children ages 5 to 17 who had received two doses of measles vaccine and attended Quebec schools where the 2011 measles outbreaks occurred were included for analysis.  Cases only included confirmed measles cases according to laboratory and clinical findings.  Controls were matched by age and school attended. Investigators compared the timing of first measles vaccine, at 12 or 13 months compared with 15 months or greater, to the risk of measles during the epidemic.  Those vaccinated at 12 or 13 months were at greater than 5 times the risk (OR = 5.27; 95% CI 1.91-14.3) of contracting measles compared to those vaccinated at 15 months.  There was no significant difference found in risk of measles for the timing of the second dose.

By Laurel Wickberg and Leah H. Carr
Reviewed by William V. Raszka, M.D.

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