Measles Seroprevalence in Infants Under 9 Months of Age in Low- and Middle-Income Countries: A Systematic Review and Meta-analysis
Darren Suryawijaya Ong, Claire von Mollendorf, Kim Mulholland, Lien Anh Ha
Abstract
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.