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 injection, which contains monoclonal antibodies, would primarily target infants and children in countries with the most malaria transmission, say 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 did not become infected after being exposed to mosquitoes carrying malaria in the lab, the researchers report on Aug. 4. New England Journal of Medicine. All six people who did not receive the drug developed infections.
The clinical trial tested different doses and delivered the drug intravenously or as an injection. Based on a computer model of how the drug is absorbed, distributed and then cleared by the body, the researchers estimate that one injection could protect against malaria for six months.
“What we’ve always been looking for is some kind of intervention that will reliably prevent infection for as long as possible,” said Miriam Laufer, a pediatric infectious disease physician and director of the Malaria Research Program at the University of Maryland School of Medicine in Baltimore. .
Ideally, Laufer says, that would be a highly effective vaccine that will provide years and years of protection. A new malaria vaccine has recently become available, but it offers only modest protection against the disease, and that protection is declining rapidly (SN: 22/12/21). The vaccine requires four shots.
Monoclonal antibodies may provide an option that requires only one injection, once a year. More research will be needed to see how well the malaria antibodies work outside the lab and how cost-effective the injection is.
The monoclonal antibody injection wouldn’t rule out the need for other prevention strategies, says Laufer, who was not involved in the new study. But it could be “one of the easier interventions in terms of minimal contact with the health care system, with good benefit.”
What’s appealing, she says, “is the possibility that you can give children, even the youngest children, an injection” [of] pre-made antibodies that can last six months or more and protect them during the rainy season.” That once-a-season injection would be helpful in countries in West Africa, 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 those deaths occurred in sub-Saharan Africa in children under the age of 5. These smallest children have not had a chance to develop immunity to the disease and are more prone to die if severe malaria develops.
Reducing the spread of malaria includes measures to control mosquitoes, such as using insecticide-treated nets over beds or spraying to kill mosquitoes indoors, as well as preventing infections, such as taking antimalarials regularly. In October 2021, the World Health Organization also recommended the new vaccine, which in clinical trials reduced the number of cases of malaria and severe malaria by 36 percent after four years of follow-up.
Monoclonal antibodies are lab-made versions of antibodies, the proteins the immune system produces in response to a vaccine or natural infection. Monoclonal means that it contains clones or copies of a particular antibody.
The antibody evaluated in the clinical trial attaches to a protein on the surface of sporozoites — the form of the malaria parasite that invades the body after an infected mosquito bites — and prevents the parasites from infecting the liver.
The new monoclonal antibody has 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 a tweak that keeps it from degrading in the body too quickly. This increases the half-life in the blood (the time it takes to break down half of the drug) to 56 days, almost three times longer than its predecessor.
Two clinical trials are planned to assess how well the drug protects children in places where malaria spreads. A trial in Mali, where malaria transmission is seasonal, will study the efficacy of the injection for seven months. Another trial in Kenya, one of the countries in East Africa where malaria spreads all year round, will assess how well the injection works while the children are followed for a year. Those studies will also help determine the best dose for children.