By Mary Hearty

A new study published in Lancet Infectious Diseases suggests that malaria booster vaccine doses are likely needed to sustain protection in children in Africa, especially those living in areas of highly seasonal malaria transmission.

Speaking during a media briefing held by the Science Media Centre United Kingdom (UK) on efficacy and immunogenicity of R21 malaria vaccine against clinical malaria after two years’ follow-up in children in Burkina Faso, Prof Sir Brian Greenwood, Professor of Tropical Medicine, London School of Hygiene and Tropical Medicine, one of the researchers involved in the study said they observed high efficacy of the malaria vaccine against first and multiple episodes of clinical malaria following the booster vaccination.

“The study reports, over 70% protection against clinical episodes of malaria in Burkinabe children over a two-year period following three priming doses of the R21 malaria vaccine, given in early life, followed by a booster dose of vaccine given just prior to the malaria transmission season, an important finding,” Prof Greenwood explained.

The study done by University of Oxford researchers recruited 450 participants aged five to 17 months from the catchment area of Nanoro, and were randomly assigned to three groups, with the first two groups receiving the R21/Matrix-M (with either a low dose or high dose of the Matrix-M adjuvant) vaccine as a booster and the third a rabies vaccine as the control group.

With the trial not including children who received just the priming doses of vaccine, Prof Greenwood said it is not possible to deduce from this paper how necessary booster doses of the R21 vaccine are to sustain protection over the first five or more years of life during which children are still at high risk of malaria in many seasonal transmission areas.

“However, the marked decline in anti-CSP antibody titre in the months after priming, as seen with the RTS,S/AS01 vaccine, and the evidence presented in this and other studies that anti-CSP antibody titre is associated with protection, suggests that booster doses are likely to be needed to sustain protection,” the Prof of tropical medicine further explained.

Furthermore, the study also indicated that the booster vaccine induced antibody concentrations that correlated with vaccine efficacy.

“We show that a single booster dose of the R21 malaria vaccine can restore high antibody concentrations. Administration of this booster dose led to sustained protective immunity over the second year when administering R21 with the higher adjuvant dose,” the researchers reported.

Last year these researchers reported results from the primary three-dose regimen that met the World Health Organization’s Malaria Vaccine Technology Roadmap goal of a vaccine with at least 75% efficacy.

Prof Azra Ghani, Chair in Infectious Disease Epidemiology at Imperial College London, said these new results demonstrating high sustained efficacy of the R21 malaria vaccine over a 2-year period are therefore very welcome.

“What is particularly encouraging from a scientific perspective are two pieces of information provided by these results; first the demonstration that antibody titres can be restored through boosting with this vaccine, and second that the antibody titres correlate with protection against clinical disease.  Taken together these indicate that similar levels of vaccine efficacy may well be achievable outside the highly seasonal setting in which this particular trial was conducted.  Such trials are currently underway as part of the wider Phase III study and results should be available later in the year,” Prof Ghani stated.

She added: “These results come at a time at which the fight against malaria is at a crossroads.  With the right investment – notably continued support for The Global Fund to Fight AIDS, TB and Malaria at their upcoming replenishment conference later this month – we can reverse recent trends and continue on the path to elimination of malaria.  Without this investment, we risk losing the gains that have been made over the last decades and witnessing a rising tide of malaria resurgence.”

Despite ongoing efforts to reduce the malaria burden – including through the provision of insecticide-treated bed nets, improvement in access to treatment, and chemoprevention — malaria continues to pose an unacceptably high burden, resulting in over 640,000 deaths globally each year, mostly in young children in Africa.