Measles Seroprevalence in Infants Under 9 Months of Age in Low- and Middle-Income Countries: A Systematic Review and Meta-analysis.

BACKGROUND

Measles infections cause significant morbidity and mortality in low- and middle-income countries (LMICs), especially in infants under 9 months of age. Measles seroprevalence data in infants too young to be vaccinated can identify immunity gaps to inform immunization strategies. Our systematic review and meta-analysis describes measles seroprevalence in infants <9 months in LMICs.

METHODS

We systematically searched journal articles and conference abstracts from 1 January 2018 to 25 December 2024 across 10 databases and registers (PROSPERO, CRD42023429586). We included observational studies presenting measles antibody seroprevalence data from infants <9 months in LMICs. Studies underwent dual reviewer screening and risk of bias was assessed using an adapted Joanna Briggs Institute tool. Seropositivity estimates were pooled using a random-effects inverse variance model. We performed subgroup analyses by country income level, measles vaccine coverage, and measles incidence.

RESULTS

Among 1421 studies identified, 34 were included. Most studies were from middle-income countries (n = 30/34) using hospital/health-center data (n = 22/34). Risk of bias was generally low or moderate (n = 33/34). The meta-analysis included 20 studies (n = 8230 infants) with high interstudy heterogeneity. Pooled seropositivity was highest at birth (81%; 95% confidence interval [CI], 75%-88%), decreasing to 30% (95% CI, 24%-35%) by 4 months, and lowest at 7 months (18%; 95% CI, 0%-41%). Subgroup analyses showed minimal differences between categories.

CONCLUSIONS

Seventy percent of infants are seronegative by 4 months old and unprotected from measles before their first vaccine dose at 9-12 months. Early administration of measles-containing vaccines could provide sustained protection throughout infancy.