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Vaccine trial against malaria shows promising results

Malaria is considered one of the deadliest mosquito-borne diseases. Image credit: Mr.Smith Chetanachan / 123rf

A new vaccine against malaria has shown promising preliminary results in a large trial in four African countries, boosting hopes that an additional tool may soon be available to help control the deadly disease.

The vaccine, named R21/Matrix-M and developed by researchers at the University of Oxford, produced similarly impressive results in a small trial last year, but the current study posed a stiffer test of its protection.

Initial data from the trial, reported on 03 November at the American Society of Tropical Medicine and Hygiene meeting in Seattle, suggest the vaccine had an efficacy higher than 70% in regions where malaria is a threat year-round as well as in places where the disease is more seasonal. “The results were very exciting,” says DeAnna Friedman-Klabanoff, a malaria vaccine researcher at the University of Maryland School of Medicine who was not involved in the study.

She and other scientists caution, however, that it is not yet clear how long the vaccine’s protection might last.

The only malaria vaccine authorized by the WHO, named RTS,S or Mosquirix, only offers partial protection, especially in areas where malaria is a threat year-round. Its efficacy drops to about 35 percent after 4 years.

The earlier R21/Matrix-M trial demonstrated that three doses given 4 weeks apart offered more than 70 percent efficacy after 1 year in 450 children in Burkina Faso. But the vaccine was given at the start of the rainy season, which lasts less than half the year and is when almost all malaria cases occur. In September, the team reported additional data showing children in that study who received a booster, again at the start of the rainy season, were protected for a second year. But the researchers have not yet reported data on whether the vaccine’s defence holds up without a booster.

Observers had been eagerly awaiting results from the larger trial, which involves 4,800 children at five sites in Burkina Faso, Mali, Kenya, and Tanzania with different patterns of malaria exposure. According to the interim data presented on 03 November, last year’s results hold up—at least for now. In areas with year-round malaria transmission, the vaccine showed 73 percent efficacy after an average of 270 days, Adrian Hill, a vaccine expert at Oxford’s Jenner Institute who is leading the project, told the meeting. In areas of seasonal transmission, the efficacy was 75 percent.

Hill told the meeting that his group is continuing to collect data and plans to publish more complete results before the end of the year. The team hopes the vaccine could be approved for wide use in the first half of 2023, he said. The world’s biggest vaccine maker, the Serum Institute of India, has already agreed to produce the shots once they’re approved and can churn out more than 180 million doses per year, about 30 times the amount of Mosquirix manufactured annually, Hill noted at the meeting. He estimated the vaccine would cost between $3 and $4 per dose.

And more on the fight against malaria. A single intravenous infusion of lab-produced monoclonal antibodies was up to 88% efficacious in preventing malaria infection in Mali, researchers reported last week. The study, in The New England Journal of Medicine, offers new hope for combatting the disease, spread by parasite-laden mosquitoes. Malaria parasites have developed resistance against many drugs, and the mosquitoes that spread them have adapted to withstand some insecticides. Researchers at the US National Institute of Allergy and Infectious Diseases developed the antibody, and working with colleagues at the University of Sciences, Techniques and Technology of Bamako, tested it or a placebo in 330 adult volunteers. The research team is now testing a more powerful antibody in 6- to 10-year-old children in Mali who are receiving the antibody by subcutaneous injection, a method that is much more practicable with young children than intravenous infusion. In 2020, malaria killed 627,000 worldwide, two-thirds of whom were children younger than 5 in Africa.

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