Effect of RTS,S/AS01(E) vaccine booster dose on cellular immune responses in African infants and children.

RTS,S/AS01(E), the first approved malaria vaccine, demonstrated moderate efficacy during the phase 3 pediatric trial. We previously investigated cell-mediated immune (CMI) responses following the primary 3-dose immunization and now report responses to the booster dose given 18 months later. Thirty CMI markers were measured by Luminex in supernatants of peripheral blood mononuclear cells from 709 children and infants after RTS,S/AS01(E) antigen stimulation, and their associations with malaria risk and antibodies one month post-booster and one year later were assessed. IL-2, IFN-γ, IL-17, IL-5, and IL-13 were associated with RTS,S/AS01(E) booster vaccination, and IL-2 responses to the circumsporozoite protein (CSP) remained higher after one year. IL-2 was associated with reduced malaria risk in one site, and IL-10 was associated with increased risk in infants. Anti-CSP IgG and IL-2 were moderately correlated one year after booster. This study highlights the moderate cell-mediated immunogenicity of the RTS,S/AS01(E) booster dose that aligns with partial recovery of RTS,S/AS01(E) vaccine efficacy.