Malaria vaccine is partly effective in young children, study shows

The first malaria vaccine to reach phase III clinical testing is partly effective against clinical disease in young children in Africa, results reported in the Lancet have shown.1

The study included 6537 infants aged 6-12 weeks and 8922 children aged 5-17 months who were enrolled at 11 centres in seven countries across sub-Saharan Africa. They were randomly assigned to receive three doses of the malaria candidate vaccine RTS,S/AS01 at months 0, 1, and 2 and a booster dose at 20 months (booster group); three doses of the malaria vaccine and a dose of comparator vaccine at 20 months (no booster group); or a comparator vaccine at all time points (control group).

Results at 18 months, reported previously, showed vaccine efficacy of about 46% against clinical malaria in the 5-17 month old children and of around 27% in the infants.2

The latest results, from following the children for a further 20-30 months, showed that the three doses of the vaccine with a booster reduced the number of clinical episodes of malaria by just over a third (36%).

“Despite the falling efficacy over time, there is still a clear benefit from RTS,S/AS01,” said the study’s lead author, Brian Greenwood, professor of clinical tropical medicine at the London School of Hygiene and Tropical Medicine. He explained that, on average, 1363 cases of clinical malaria were prevented over four years of follow-up for every 1000 of the older children who were vaccinated and 1774 cases in those who also received a booster. In infants, an average of 558 cases were averted over three years for every 1000 infants vaccinated and 983 cases in those also given a booster.

“Given that there were an estimated 198 million malaria cases in 2013, this level of efficacy potentially translates into millions of cases of malaria in children being prevented,” said Greenwood.

Vaccination significantly reduced the overall number of admissions to hospital, admissions relating to malaria, cases of severe anaemia, and the need for blood transfusion in children, with greater protective effects seen in those given a booster dose.

Serious adverse events were reported in about a quarter of children in the trial, with a similar incidence in all study groups, although only 0.3% of these were judged to be related to the vaccine. More cases of meningitis were seen in children vaccinated at the age of 5-17 months than in the controls, with five new cases being recorded from month 21 to the end of the trial in the vaccinated groups but none in the control group. This imbalance was not seen in the young infants.

The European Medicines Agency will now review the data. Greenwood said, “If the EMA gives a favourable opinion, WHO could recommend the use of RTS,S/AS01 as early as October this year. If licensed, RTS,S/AS01 would be the first licensed human vaccine against a parasitic disease.”

In an associated editorial Vasee Moorthy and Jean Marie Okwo-Bele, from the Department of Immunization, Vaccines and Biologicals at the World Health Organization in Geneva, said, “The donor community would need to coordinate any financing for the RTS,S/AS01 vaccine carefully, should it reach that stage. In particular, funding must not be redirected away from meeting adequate access to artemisinin-combination treatments, rapid diagnostic tests, longlasting insecticidal nets, and other malaria control measures already in place in certain settings.”3