Waning of measles immunity by 5 years of age following an accelerated two-dose measles vaccine schedule at 6 and 12 months in South African children: an observational cohort study

BACKGROUND: Accelerated measles vaccine dosing schedules in infants is being considered to mitigate susceptibility to measles in young infants. We evaluated the persistence of measles antibodies at 3 and 5 years of age in children who had received a two-dose schedule at 6 and 12 months of age. METHODS: We followed a cohort of enrolled children who had received the measles vaccine (CAM-70 strain; MeasBio™) at 6 and 12 months of age. Blood samples were obtained at 3 and 5 years of age and tested for serum measles immunoglobulin G (IgG) using the Euroimmun Measles IgG ELISA Kit. Seropositivity was defined as an anti-measles IgG titre ≥153 mIU/mL. RESULTS: We analysed samples from 115 HIV-unexposed and 38 HIV-exposed-uninfected (HEU) children. The prevalence of measles IgG seropositivity was 73.9% (95% CI: 66.7-80.4%; 113/153) and 60.8% (95% CI: 52.9-68.6%; 93/153) at 3 and 5 years of age, respectively. There were no differences in measles IgG seropositivity or geometric mean IgG titres between HIV-unexposed and HEU children at either time point. INTERPRETATION: An accelerated two-dose measles vaccine schedule during infancy is associated with waning of immunity by 3 years of age, indicating the need for a booster dose in early childhood. FUNDING: This study was funded in part by the South African Medical Research Council through its Division of Research Capacity Development under the Chan Soon-Shiong Family Foundation Scholarship Programme.