Scientists have found that a malaria vaccine candidate, which had shown promise in the fight against the mosquito-borne disease, stops working in children after four years.
Researchers from KEMRI-Wellcome Trust Research Programme and Oxford University researchers in Kenya found that the efficacy of the candidate RTS,S vaccine dropped from 43.6 per cent protection against malaria in the first year to zero by the fourth year after vaccination.
Malaria remains an important cause of illness and death among children in sub-Saharan Africa, and there is currently no vaccine that offers complete protection against the disease.
RTS,S is the most advanced candidate malaria vaccine and entered phase III clinical trials in Africa in 2009.
In Kilifi, Kenya, 447 children had been part of an earlier phase II trial to assess the safety and efficacy of the vaccine candidate. Of the 447 children, 320 completed four years of follow-up.
Initial results from larger ongoing phase III studies showed that the candidate RTS,S vaccine reduced malaria over 12 months of follow-up by approximately half in young children and one-third in infants.
The new findings on long-term follow-up of an earlier phase II study reveal that the vaccine efficacy dropped from 43.6 per cent protection against malaria in the first year to zero by the fourth year after vaccination.
"Despite the falling efficacy over time, there is still a clear benefit to the vaccine candidate," said study's senior author, Dr Phillip Bejon.
"Many of the children will experience multiple episodes of clinical malaria infection, but overall we found that 65 cases of malaria were averted over the four-year period for every 100 children vaccinated. We now need to look at whether offering a vaccine booster can sustain efficacy for longer," said Bejon, Research Fellow at the KEMRI-Wellcome Trust Research Programme and the Centre for Tropical Medicine, University of Oxford.
The study, published in the New England Journal of Medicine, also found that relative vaccine efficacy declines with increasing exposure to malaria, from 45.1 per cent among children with below-average exposure to malaria to 15.9 per cent among children with above-average exposure to malaria.
Latest figures estimate that there are 1.44 billion people living in regions of stable malaria transmission worldwide. Most deaths occur among children living in Africa, where a child dies from malaria every minute.
