Antibody responses in children born to vaccinated mothers were lower because of earlier administration of their first measles vaccine dose at 12 months of age or younger, compared with 15 months of age or older, said Sara Carazo Perez, MD, PhD, of Laval University, Quebec City, and her associates.

Studies suggest that measles elimination “requires the maintenance of population immunity above 92%-94%.” So, “the additional protection of 3%-5% of vaccinated children against secondary vaccine failures by postponing the first dose from 12 to 15 months of age would be significant, and the risk would be minimal in countries that achieved elimination” of measles, said Dr. Perez and her colleagues.

Data combined from five randomized, controlled trials involving several countries assessing immunogenicity of the trivalent vaccine MMR or the tetravalent vaccine MMRV, which includes varicella, allowed evaluation of 2,617 children (born to mostly vaccinated mothers) who received two doses of vaccine and were followed for 1-3 years.

The percentage of children who were seronegative for measles after being vaccinated decreased significantly with older age at the first dose, from 8.5% in children vaccinated at 11 months to 3.2%, 2.4%, and 1.5% with vaccination at 12 months, 13-14 months, and 15-22 months, respectively (P less than .001).

Geometric mean concentrations (GMC) after the second dose were highly correlated with GMCs after the first dose.

The investigators then performed multivariable analysis, adjusting for the type of vaccine, the country, and the study. GMCs rose significantly with older age at first dose. Children vaccinated at 11 months had a 23% lower GMC and 30% increased risk of seronegativity than children vaccinated at 12 months.

In children first vaccinated at 13-14 months or 15-22 months, GMCs were 1.21 and 1.37 times greater than in children vaccinated at 12 months, respectively, and their risks for seronegativity were 49% and 71% lower, respectively.

“After two doses, the association between the age at first dose and the GMC was slightly weaker but still significant,” the researchers said.

Read more in the journal Clinical Infectious Diseases (2017 Jun 8. doi: 10.1093/cid/cix510 ).