The protection provided by the world’s first malaria vaccine all but disappears after seven years, according to a new study. A phase-two clinical trial of Mosquirix (RTS,S) in Kenya showed just 4 percent effectiveness in children older than 7 years. With an already relatively low rate of malaria prevention, this is another setback for GlaxoSmithKline, the developer of the vaccine.
“The reduced exposure to blood-stage parasites among persons who have received the RTS,S/AS01 vaccine may lead to a slower acquisition of immunity to blood-stage parasites, leading to an increase in episodes of clinical malaria in later life,” according to the study, published in the New England Journal of Medicine.
More than 440 children were tracked over seven years. Half of the children received three doses of the vaccine and half did not get it at all. In the first year, vaccinated children were 35.9 percent less likely to get malaria compared to the unvaccinated group. That difference fell to only 4.4 percent after seven years.
Earlier research showed that protection rates fell to 28 percent after 4 years. Children who got a fourth dose fared better, spurring discussions to increase the regimen. This newer extended look at a small group of children raises the possibility that protection disappears soon after. It is not good news, but it does not necessarily mean the vaccine is a failure.
“While our results raise the possibility that being exposed to very high levels of malaria parasites may undo some of the benefits of RTS,S, our sample size was too small to draw any definitive conclusions about the long-term efficacy of the vaccine,” said Philip Bejon, study co-author and the director of the KEMRI-Wellcome Trust Research Program, in a release.
With more than 400,000 people dying of malaria each year, there is a great need for medicines that can treat and prevent the parasite. The Mosquirix vaccine was developed with the hope of preventing infections entirely. The product was developed by major pharmaceutical company GlaxoSmithKline with support from the PATH Malaria Vaccine Initiative and funding from the Bill & Melinda Gates Foundation.
Based on previous research on the vaccine, the World Health Organization recommended an evaluation of a four-dose regimen. Such a study will be rolled out in the near future, adding to the existing evidence base and the information currently being gathered in other studies of the three-dose variant. It is possible even more doses will be needed to extend the protection of the vaccine in children – the group most vulnerable to malaria.
“The results suggest that the implementation of RTS,S will need to be considered carefully and in a way that takes into account different levels of malaria exposure,” said Mike Turner, head of infections at the Wellcome Trust, in a release “RTS,S isn’t perfect, but it still has the potential to save lives and will provide an important springboard for improved second generation vaccines that target multiple stages of the malaria parasite’s lifecycle.”
Whether the imperfect vaccine has as much potential as its developers and supporters say is still uncertain. An OpEd accompanying the study urged caution when reading the new results, but said that more research is needed to understand just how well the drug works in preventing malaria over both the short term and long term. It may become a tool to help reduce malaria deaths, but it is a long way from being the vaccine that could end malaria entirely.