A shot of immune proteins can protect against malaria for months

A single injection that could provide months of protection against malaria has been shown to be effective and safe in a small, early clinical trial in adults.

The vaccine, which contains monoclonal antibodies, would be targeted primarily at infants and children in countries with the highest malaria transmission, according to the team that conducted the trial. These young children are most at risk of dying from severe malaria.

In the clinical trial, 15 of the 17 participants who received the monoclonal antibodies were not infected after being exposed to mosquitoes with malaria in the laboratory, the researchers report in August 4. New England Journal of Medicine. The six people who did not receive the drug developed infections.

The clinical trial tested different doses and administered the drug intravenously or by injection. Based on a computer model of how the drug is absorbed, distributed and then eliminated by the body, the researchers estimate that one injection can protect against malaria for six months.

“What we’ve always looked for is some sort of intervention that would reliably prevent infection for as long as possible,” says Miriam Laufer, a pediatric infectious disease physician and director of the malaria research program. at the University of Maryland. Baltimore School of Medicine.

Ideally, Laufer says, it would be a highly effective vaccine that provides years and years of protection. A new malaria vaccine has recently become available, but it provides only modest protection against the disease, and this protection wanes rapidly (SN: 12/22/21). The vaccine requires four injections.

Monoclonal antibodies could provide an option that requires only one injection, once a year. More research will be needed to see how well antibodies work against malaria outside of the lab and how cost-effective the vaccine is.

Injecting monoclonal antibodies would not preclude the need for other prevention strategies, says Laufer, who was not involved in the new study. But it could be “one of the easiest interventions in terms of minimal contact with the healthcare system, with good benefits.”

What’s appealing, she says, “is the ability to inject even the youngest children. [of] pre-made antibodies that could last six months or more and protect them through the rainy season. This once-per-season vaccine would be useful in West African countries, where malaria transmission only occurs during the rainy season.

Malaria sickened an estimated 241 million people and killed 627,000 worldwide in 2020. Most of these deaths occurred in sub-Saharan Africa in children under the age of 5. These smaller children have not had a chance to develop immunity to the disease and are more likely to die if severe malaria develops.

Reducing the spread of malaria includes mosquito control measures, such as using insecticide-treated mosquito nets above beds or spraying to kill mosquitoes indoors, as well as infection prevention , such as taking antimalarial drugs at regular intervals. In October 2021, the World Health Organization also recommended the new vaccine, which in clinical trials reduced cases of malaria and severe malaria by 36% after four years of follow-up.

Monoclonal antibodies are laboratory-made versions of antibodies, the proteins that the immune system produces in response to a vaccine or natural infection. Monoclonal means it contains clones or copies of a particular antibody.

The antibody being evaluated in the clinical trial attaches to a protein on the surface of sporozoites – the form of the malaria parasite that enters the body after the bite of an infected mosquito – and prevents the parasites from infecting the liver .

The new monoclonal antibody features improvements over an earlier version developed by the same research team. The new version binds more strongly to the target protein of the malaria parasite. It also has an adjustment that prevents it from breaking down too quickly in the body. This increases its blood half-life (the time it takes for half the drug to break down) to 56 days, almost three times that of its predecessor.

Two clinical trials are planned to assess how well the drug protects children in places where malaria is spreading. A trial in Mali, where malaria transmission is seasonal, will study the effectiveness of the vaccine for seven months. Another trial in Kenya, among East African countries where malaria spreads year-round, will assess the effectiveness of the vaccine while following children for a year. These studies will also help determine the best dose for children.

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