Experimental malaria vaccine confers modest, short-term protection

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1. Efficacy of the RTS,S/AS01E vaccine wanes over four years.

2. The decline in efficacy is greater in areas of higher malaria exposure. 

The RTS,S/AS01E is currently the most developed malaria vaccine, with its phase 3 trial slated to end in December 2014. Results continue to show that the vaccine provides a real protective effect, though the effect size is modest. At this point, it seems likely that the vaccine will augment rather than replace existing prevention and treatment methods.

This study and others like it provide data upon which evidence-based guidelines for the application of this vaccine can be based. In particular, the finding that vaccine efficacy declines over four years, especially in areas with high rates of malaria, has important implications. In the future, the authors’ method of calculating the malaria exposure index may become part of the criteria used to determine where the vaccine could be usefully deployed.

Click to read the study, published today in NEJM

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Image: PD

1. Efficacy of the RTS,S/AS01E vaccine wanes over four years.  

2. The decline in efficacy is greater in areas of higher malaria exposure.

This [randomized] study: In a previous phase 2 study, children in sub-Saharan Africa aged 5 to 17 months, were randomly assigned to receive either an experimental malaria vaccine (RTS,S/AS01E) or a rabies vaccine. This study presents the four-year follow-up data from one of the study sites — Kilifi, Kenya.

The efficacy of the vaccine declined over the four-year period. The authors calculated that the numbers of malaria cases prevented per 100 children vaccinated in each year of follow-up were: 26, 22, 18 and -1. The incidence rate of malaria episodes in year four was the same in the vaccinated and control groups.

The efficacy of the vaccine over four years was also affected by intensity of malaria exposure. In the high exposure index group, the vaccinated and unvaccinated groups both had a similar incidence of malaria episodes by year four. In the low exposure index group, the vaccinated group continued to have a lower incidence of malaria in the fourth year.

In sum: The RTS,S/AS01E is currently the most developed malaria vaccine, with its phase 3 trial slated to end in December 2014. Results continue to show that the vaccine provides a real protective effect, though the effect size is modest. At this point, it seems likely that the vaccine will augment rather than replace existing prevention and treatment methods.

This study and others like it provide data upon which evidence-based guidelines for the application of this vaccine can be based. In particular, the finding that vaccine efficacy declines over four years, especially in areas with high rates of malaria, has important implications. In the future, the authors’ method of calculating the malaria exposure index may become part of the criteria used to determine where the vaccine could be usefully deployed.

Click to read the study, published today in NEJM

By Tomi Jun and Mitalee Patil

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