Timing of antiretroviral treatment initiation and seropositivity to measles virus among children living with HIV in rural Zambia.

Background: Combination antiretroviral therapy (cART) reduces morbidity among children living with HIV (CHIV) but does not restore measles immunity. Many CHIV now initiate cART before measles vaccination but the impact on measles-specific immunity is not understood. This study compared measles antibodies between CHIV initiating cART before and after 9 months of age in Zambia. Methods: This retrospective study was nested within an open cohort study of CHIV and community-based malaria studies in Macha, Zambia conducted from 2007-2020. Samples were tested for measles IgG antibodies from CHIV defined by age at cART initiation (aged 0-8, 9-23, and 24-59 months) and age-matched community-based controls. A cross-sectional analysis compared antibody concentrations between CHIV groups after 6-12 months of cART and aged >12 months and controls. A longitudinal analysis evaluated antibody trajectories from 9 months of age through 48 months of cART and during the 2010-11 measles outbreak. Results: In the cross-sectional analysis, 31.9% of 301 CHIV were seropositive after 6-12 of cART, with no significant difference by group (0-8: 30.8%; 9-23: 37.0%; 24-59 months: 26.6%). Within each CHIV group, the proportion seropositive was significantly lower than age-matched controls. Among 242 CHIV included in the longitudinal analysis, 46-56% had an antibody response, with an estimated time to seroreversion of 1.8-3.2 years. Among CHIV followed in 2010-11, 50% seroconverted or boosted; the estimated time to seroreversion was 2.1 years. Conclusions: Low levels of measles antibodies were found among CHIV, even when cART was started before 9 months of age, supporting a recommendation that CHIV, including infants, would benefit from revaccination.