New England Journal of Medicine
March 21, 2013  Vol. 368 No. 12
http://www.nejm.org/toc/nejm/medical-journal

Original Article
Four-Year Efficacy of RTS,S/AS01E and Its Interaction with Malaria Exposure
Ally Olotu, M.B., Ch.B., Gregory Fegan, Ph.D., Juliana Wambua, B.Sc., George Nyangweso, B.Sc., Ken O. Awuondo, H.N.D., Amanda Leach, M.R.C.P.C.H., Marc Lievens, M.Sc., Didier Leboulleux, M.D., Patricia Njuguna, M.B., Ch.B., Norbert Peshu, M.B., Ch.B., Kevin Marsh, F.R.C.P., and Philip Bejon, Ph.D.
N Engl J Med 2013; 368:1111-1120March 21, 2013DOI: 10.1056/NEJMoa1207564
http://www.nejm.org/doi/full/10.1056/NEJMoa1207564

Background
The candidate malaria vaccine RTS,S/AS01E has entered phase 3 trials, but data on long-term outcomes are limited.
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Methods
For 4 years, we followed children who had been randomly assigned, at 5 to 17 months of age, to receive three doses of RTS,S/AS01E vaccine (223 children) or rabies vaccine (224 controls). The end point was clinical malaria (temperature of ≥37.5°C and Plasmodium falciparum parasitemia density of >2500 parasites per cubic millimeter). Each child’s exposure to malaria was estimated with the use of the distance-weighted local prevalence of malaria.
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Results
Over a period of 4 years, 118 of 223 children who received the RTS,S/AS01E vaccine and 138 of 224 of the controls had at least 1 episode of clinical malaria. Vaccine efficacies in the intention-to-treat and per-protocol analyses were 29.9% (95% confidence interval [CI], 10.3 to 45.3; P=0.005) and 32.1% (95% CI, 11.6 to 47.8; P=0.004), respectively, calculated by Cox regression. Multiple episodes were common, with 551 and 618 malarial episodes in the RTS,S/AS01E and control groups, respectively; vaccine efficacies in the intention-to-treat and per-protocol analyses were 16.8% (95% CI, −8.6 to 36.3; P=0.18) and 24.3% (95% CI, 1.9 to 41.6; P=0.04), respectively, calculated by the Andersen–Gill extension of the Cox model. For every 100 vaccinated children, 65 cases of clinical malaria were averted. Vaccine efficacy declined over time (P=0.004) and with increasing exposure to malaria (P=0.001) in the per-protocol analysis. Vaccine efficacy was 43.6% (95% CI, 15.5 to 62.3) in the first year but was −0.4% (95% CI, −32.1 to 45.3) in the fourth year. Among children with a malaria-exposure index that was average or lower than average, the vaccine efficacy was 45.1% (95% CI, 11.3 to 66.0), but among children with a malaria-exposure index that was higher than average it was 15.9% (95% CI, −11.0 to 36.4).
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Conclusions
The efficacy of RTS,S/AS01E vaccine over the 4-year period was 16.8%. Efficacy declined over time and with increasing malaria exposure.

(Funded by the PATH Malaria Vaccine Initiative and Wellcome Trust; ClinicalTrials.gov number, NCT00872963.)