Clin Infect Dis. 2021 Dec 11:ciab1017. doi: 10.1093/cid/ciab1017. Online ahead of print.
BACKGROUND: A trial in young African children showed that combining seasonal vaccination with the RTS,S/AS01E vaccine with seasonal malaria chemoprevention reduced the incidence of uncomplicated and severe malaria substantially compared to either intervention given alone. This paper reports the anti-circumsporozoite antibody response to seasonal RTS,S/AS01E vaccination in children in this trial.
METHODS: Sera from a randomly selected sub-set of children collected before and one month after three priming doses of RTS,S/AS01E and before and one month after two seasonal booster doses were tested for anti-circumsporozoite antibodies by ELISA. The association between post vaccination antibody titer and incidence of malaria was explored.
RESULTS: A strong anti-circumsporozoite antibody response to three priming doses of RTS,S/AS01E was seen (Geometric Mean Titer, GMT 368.9 EU/ml) but titers fell markedly prior to the first booster dose. A strong antibody response to an annual, pre-malaria transmission season booster dose was observed in primed children but this was lower than after the primary vaccination series and lower after the second than after the first booster dose (ratio of geometric mean rise 0.66 [95% CI: 0.57, 0.77]). Children whose antibody response was in the upper tercile post-vaccination had a lower incidence of malaria during the following year than children in the lowest tercile (hazard ratio 0.43 [95% CI 0.28,0.66].
CONCLUSION: Seasonal vaccination with RTS,S/AS01E induced a strong booster antibody response which was lower after the second than after the first booster dose. However, the diminished antibody response to the second booster dose was not associated with diminished efficacy.