The world's first malaria vaccine could potentially prevent up to one in four malaria deaths in young children, predict scientists.

In a new study, published today in The Lancet, scientists from Imperial College London and other international institutions used mathematical models to predict the effectiveness of the vaccine.
 
Known as RTS,S, the vaccine is designed to prevent malaria disease caused by the P. falciparum parasite, and its effectiveness was demonstrated in large-scale trials in Africa last year. In the trials, the vaccine was found to have an efficacy of 43.9 percent in children aged 5-17 months, and 27.8 percent in infants aged 6-12 weeks over 4 years. Children received the vaccine four times between birth and two years old.

The WHO estimates there have been 214 million new malaria cases and 438,000 malaria deaths in 2015, the vast majority in sub-Saharan Africa. Despite progress, malaria remains a leading cause of death in children in this region. The new study contributes to the scientific evidence being considered by the World Health Organization (WHO), which is assessing the malaria vaccine for use in Africa.

In the study, researchers used data from the vaccine trials to predict large-scale effectiveness, if it was rolled-out across areas in sub-Saharan Africa with moderate to high levels of malaria. They found that over a 15 year time period, 484 deaths would be averted for every 100,000 children vaccinated. Because children experience repeated attacks of malaria in the first few years of life, for every 100,000 children vaccinated, an average of 116,500 cases of malaria disease would be averted.

The authors stress that the results account for vaccine use alongside long-lasting insecticide-treated bed nets.

“Our numbers indicate that 6 to 29 percent of malaria deaths in children younger than age five could potentially be averted by the vaccine in the areas in which it is implemented, when used alongside other malaria control interventions,” said Dr Melissa Penny, one of the study authors, from the Swiss Tropical and Public Health Institute.

The scientists also found that the vaccine would be cost effective at USD$5 or less per dose, in areas of moderate and high malaria transmission.
 
“The cost-effectiveness of the vaccine is similar to what we’ve seen for other recently introduced childhood vaccines,” said Professor Azra Ghani, an author of the study from Imperial’s School of Public Health. “It also overlaps within the ranges of cost-effectiveness of other malaria control interventions like bed nets and indoor residual sprays. However, it is important that the vaccine is introduced in addition to these other highly cost-effective interventions.”

The authors cautioned there is still uncertainty over the long-term efficacy of the vaccine, as the previous trials have only tracked children for four years following immunisation. Furthermore, since trials of the vaccine were not large enough to test for reduction in deaths from malaria, and the quality of care provided to study participants was high, the projection of deaths requires further validation.
 
“It will be important to continue to track the long-term impact of this vaccine to ensure that the effectiveness predicted by the models is borne out in practice,” said Dr. Caitlin Bever of the Institute for Disease Modelling.
 
The vaccine has been developed by GSK in partnership with the PATH Malaria Vaccine Initiative.  

"Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models" is published in the Lancet.