According to a study published early online in the New England Journal of Medicine, an experimental malaria vaccine from GlaxoSmithKline halved the risk of African children getting malaria in a major clinical trial.

The phase III study, conducted between the period March 2009 and January 2011 involved a total of 15,460 children in two age categories, 6 to 12 weeks of age and 5 to 17 months of age, who were randomised to receive vaccination with either RTS,S/AS01 (a malaria vaccine) or a non-malaria comparator vaccine. The primary end point of the analysis in the currently ongoing study, was vaccine efficacy against clinical malaria during the 12 months after vaccination in the first 6000 children 5 to 17 months of age at enrollment who received all three doses of vaccine according to protocol. After 250 children had an episode of severe malaria, vaccine efficacy against severe malaria in both age categories was evaluated.

The following results were reported:

• During 12 months of follow-up in the first 6000 children in the older age category, the incidence of the first or only episode of clinical malaria meeting the primary case definition was 0.44 per person-year in the RTS,S/AS01 group and 0.83 per person-year in the control group, resulting in a vaccine efficacy of 55.8% (97.5% confidence interval [CI], 50.6 to 60.4).

• At least one episode of severe malaria that met the primary case definition occurred in 57 of 2830 children (2.0%) in the RTS,S/AS01 group and in 56 of 1466 children (3.8%) in the control group, for a vaccine efficacy of 47.3% (95% CI, 22.4 to 64.2)

• Among children in the combined age categories, at least one episode of severe malaria that met the primary case definition occurred in 149 of 8597 children (1.7%) in the RTS,S/AS01 group and in 116 of 4364 children (2.7%) in the control group (p<0.001).

• In the older age category, serious adverse events were reported in 1048 of 5949 children (17.6%; 95% CI, 16.7 to 18.6) in the RTS,S/AS01 group and in 642 of 2974 children (21.6%; 95% CI, 20.1 to 23.1) in the control group. In the younger age category, the corresponding rates were 569 of 4358 children (13.1%; 95% CI, 12.1 to 14.1) in the RTS,S/AS01 group and in 293 of 2179 children (13.4%; 95% CI, 12.0 to 15.0) in the control group.

The study is still ongoing and further details of the combined age-group analysis and the analysis for the lower age group is anticipated in a year.

The researchers conclude that these initial results show that the RTS,S/AS01 vaccine reduced malaria by half in children 5 to 17 months of age during the 12 months after vaccination and that the vaccine has the potential to have an important effect on the burden of malaria in young African children. Additional information on vaccine efficacy among young infants and the duration of protection will be critical to determining how this vaccine could be used most effectively to control malaria.