Research scientists have revealed that the effects of malaria vaccine wears off to almost nothing after seven years.
The researchers, who published a long-term study of the vaccine – called RTS,S or Mosquirix – designed for children in Africa, said the decline in its efficacy over time is fastest in children living in areas with higher than average rates of malaria.
As the malaria vaccine wears off, the study shows that children living in areas where there is high transmission of the disease end up with more infections than those who have never had a jab – known as the malaria rebound effect. Unvaccinated children – if they survive malaria – develop some natural immunity over the years.
For this latest study, published in the New England Journal of Medicine, researchers at the KEMRI-Wellcome Trust research program in Kilifi, Kenya, followed 447 children who had received three doses of either Mosquirix or a control vaccine when they were 5 to 17 months old. After seven years, there were 312 children still involved in the study.
The results showed that during the first year, the risk of getting malaria in the vaccinated children was 35.9 percent less than in the control group, but after seven years this difference fell to 4.4 percent.
After five years, in children exposed to higher than average rates of malaria, there were more cases (1,002) in the vaccinated group compared with the control group (992).
Director of the KEMRI programme, Philip Bejon, said this “rebound” effect is thought to be caused by the vaccinated children developing their natural immunity against malaria more slowly than unvaccinated children.
It is further suggested that a four-dose schedule and potentially a 5th and 6th dose would be needed if Mosquirix would play a meaningful role in fighting malaria.
Despite its limited efficacy, Mosquirix last year became the first ever malaria vaccine to win regulatory approval, when the European Medicines Agency gave it a green light.
The WHO, meanwhile, has said that Mosquirix is promising in its potential to reduce cases of malaria, but should be deployed only on a pilot basis before any wide-scale use.
The RTS,S vaccine, as it is called, was greeted as a breakthrough even though it only offers partial protection; 39% among children given four shots starting between five and 17 months of age.
Malaria, a mosquito-borne parasitic disease, kills around 400,000 people a year, the vast majority of them children and babies in sub-Saharan Africa. World Health Organization (WHO) data show there are around 200 million malaria cases a year.