The waning of maternal measles antibodies: A multi-country maternal-infant seroprevalence study

To assess geographical variation in maternal measles antibody levels from birth to nine months of age, to inform recommendations for the timing of the first measles vaccine dose.

Stored infant serum samples from 11 countries taken at delivery and/or follow-up time points prior to measles vaccination (N=2845) were tested for measles plaque reduction neutralisation (PRNT) and measles, mumps, and rubella immunoglobulin G at a central laboratory. Antibody decay in infants was modelled using linear mixed effects models with participant-level random intercepts and random slopes. Proportions of infants with antibody concentrations above the clinical protection threshold (0.12 IU/mL) were estimated at each age.

At birth, most (94%, 519/552) infants had PRNT ≥0.12 IU/mL, but geometric mean concentrations ranged from 0.32 IU/mL (Guatemala) to 1.60 IU/mL (Pakistan). There was no geographical variation in the decay rate of PRNT nor immunoglobulin G. Geometric mean PRNT fell below 0.12 IU/mL between ages 2.5 months (Guatemala) and 6.2 months (Pakistan). At age 6 months, <50% of infants had PRNT ≥0.12 IU/mL in all countries except Pakistan.

Reliance on maternal antibodies for protection until age 9 months or later leaves most infants with insufficient direct protection against measles infection between ages 6-9 months.