Infants’ protection against measles from mom’s antibodies wears off quickly, leaving them susceptible most of the time up until their 12-month vaccination, researchers found.

Maternal antibodies conferred immunity for a median of only 0.97 months among infants of vaccinated women, Elke Leuridan, MD, of the University of Antwerp, Belgium, and colleagues reported online in BMJ.

Infants of women with naturally-acquired immunity stayed protected longer, with a median of 3.78 months until sufficient levels of the maternal measles antibodies disappeared.

By six months of age, more than 99% and 95% of infants, respectively, had lost all their maternal antibodies against measles, according to the prospective study.

Moving routine measles vaccination to an earlier age, such as 9 months or even before that, might be reasonable if studies affirm that this is effective, Leuridan’s group suggested.

The CDC and other organizations recommend the measles/mumps/rubella vaccination at 12 months of age in part to wait for the immune system to mature to the point where an efficient response to the vaccine would produce immunity.

However, earlier vaccination should be considered for exposed children or in an outbreak situation, which is becoming an increasing concern due to vaccine refusals in the developed world and travel to endemic areas, Leuridan and colleagues said.

For other children, these data emphasize the “extreme importance” of administration of the first dose of the measles-containing vaccine on schedule, without delay, they added.

They pointed to an increasing gap of susceptibility for infants overall, whether the mother got a higher titer of antibodies from naturally-acquired immunity or not.

Prior studies have shown declining levels of maternal measles antibodies in children over time as more mothers have gotten their immunity from vaccination and as the average age at pregnancy has risen.

So to see “whether the amount of maternal antibodies is still sufficient to protect infants until the first dose of vaccine is administered in the era of changing measles epidemiology,” the researchers conducted a prospective, longitudinal study of 207 healthy pairs of women and their infants delivered at five hospitals in the province of Antwerp.

Among these women, the 120 with natural immunity carried substantially higher immunoglobulin G antibody titers to measles than the 87 who had been vaccinated with a single dose during childhood (geometric mean 2,687 versus 779 mIU/ml, P<0.001).

These maternal values at 36 weeks of pregnancy correlated with infant antibody levels at birth as measured in cord blood, such that infants of vaccinated women remained at lower antibody concentrations at the one-, six-, nine-, and 12-month follow-up visits (all P<0.001).

By 3 months of age, immunity remained in 29% of infants of vaccinated women and 60% of infants born to women with naturally-acquired immunity.

This dropped to just 15% overall at age 6 months, all but one of those born to naturally-immune women.

None remained "positive" for maternal antibodies at age 9 or 12 months.

None of the factors considered in a model appeared to impact loss of these antibodies, including breast-feeding, parity, gestational age, birth weight, mother's educational level, day care attendance, and cesarean section.

The researchers cautioned that the threshold level they used for determining protection against measles might have been questionable despite common use in practice.

These findings likely are generalizable beyond the study population, since the antibody titers in the study matched those seen in the general population of women of childbearing age in the same area, they noted.

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The study was funded by a research grant from the University of Antwerp and an unrestricted educational grant from GlaxoSmithKline Belgium.

The researchers reported no conflicts of interest.

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Primary source: BMJ
Source reference:
Leuridan E, et al “Early waning of maternal measles antibodies in era of measles elimination: longitudinal study” BMJ 2010; 340: c1626.