Backgrounds:

The presence of maternal transplacental measles antibodies in infants can prevent infection in early life but also suppress the infant response to the first measles vaccine.

Methods

We explored factors associated with antibody levels in mothers and infants at birth, and the decay of antibody in the first year of life in a multicountry seroprevalence study to determine the decay of maternal antibodies and loss of protection, and whether these vary geographically. Stored sera from mothers and infants were shipped to a central laboratory for evaluation of anti-measles IgG by multiplex immunoassay and plaque reduction neutralisation titres (PRNT). Data from the first five countries were available for analysis (Mali, Thailand, The Netherlands, UK, Vietnam)

Log-transformed data were compared using linear models adjusting for country. Decay models included polynomial terms and infant level random intercepts to account for the repeated timepoints.

Results:

Higher measles serum IgG and PRNT were statistically associated with maternal age, in both maternal samples (IgG p=0.001, PRN p=0.003) and cord blood (IgG p=0.037, PRN p=0.015). Maternal age was also statistically significantly related to the WHO measles vaccine coverage during the mother’s year of birth, indicating that older mothers are less likely to have been vaccinated in early life than younger mothers resulting in higher antibody in later life from childhood infection.

Measles IgG and PRNT in infant samples decayed at a similar rate across all countries in the first 6 months of life. Average PRNT were below protective thresholds (120 mIU/ml) by 6 months of age for all countries. For anti-measles IgG, all countries had seronegative estimates at 9 months of age.

Conclusions/Learning Points:

Infants older than 6 months are susceptible to measles infection. These results can inform vaccination programmes.