March 30, 2023

A malaria vaccine shows promising results in clinical trials

A malaria vaccine shows promising results in clinical trials
A malaria vaccine shows promising results in clinical trialsA malaria vaccine shows promising results in clinical trials

RESEARCHERS HAVE tried to develop an effective malaria vaccine for decades. But this has proved tricky. One of the main challenges is the very nature of the disease. Plasmodium species, the parasites that cause malaria, are extremely good at evading the body’s immune-system response. The World Health Organisation (WHO) estimates that more than 400,000 people a year die after becoming infected with them. Most are children in Africa. But results from a clinical trial of a new vaccine suggest that, if it can be got to those who need it, this could change.

On April 23rd a group led by Halidou Tinto, a professor of parasitology who is the regional director of the Research Institute of Health Sciences in Nanoro, Burkina Faso, announced that their candidate vaccine, developed at Oxford University and called R21/Matrix-M (MM), was 77% effective in preventing malaria over the course of a year. This result is both impressive and unprecedented. It is the first time such a vaccine has met the 75% efficacy threshold set by the WHO.

The phase-2 trial, designed to determine whether the vaccine provoked an immune response that would fight off an infectious agent, recruited 450 children in Burkina Faso, aged 5-17 months. Participants were divided into three groups. Members of two of these were given low and high doses of R21/MM respectively. Members of the third, who served as controls, received rabies shots instead. Among those given the lower dose, efficacy was 74%, slightly lower than for those who had the higher dose. None of the participants reported any serious effects as a result of vaccination. A larger, phase-3, trial is planned to begin in the coming weeks.

Dozens of malaria vaccines have undergone clinical trials in recent years, but none has shown efficacy rates high enough to enter the market. Even RTS,S/AS01, developed by GlaxoSmithKline, a British pharmaceutical firm, and the most effective candidate to date, offered only 55.8% protection when tested in a phase-3 trial. But this jab also sometimes caused serious complications including meningitis. R21/MM is an improved version of RTS,S/AS01. Both employ the same antigen (a molecule called circumsporozoite, found on the parasite’s surface, which the vaccine trains the immune system to recognise and attack), but in R21/MM it is packaged chemically in a way that makes it more effective.

Not only is R21/MM more protective and safer than RTS,S/AS01, it is also cheaper. According to Adrian Hill, director of Oxford University’s Jenner Institute, where the vaccine was developed, and a co-author of the paper in which the findings were published, it would only cost a few dollars per dose. The Serum Institute of India, one of the world’s largest producers of vaccines, has agreed to deliver at least 200m doses a year once it is granted approval. The Oxford researchers are also looking to add other components to bring the new vaccine’s efficacy closer to 100%, though even then a booster shot is likely to be needed a year after the initial jab, so that the immune system remains well prepared.

If and when R21/MM is approved for use, there will still be hurdles to leap before it can be deployed. Many African countries still have poor medical infrastructure. Dr Hill says it may be challenging for some to add yet another vaccine to the ten or so that many African children already receive. “A malaria vaccine is going to be one of the most important vaccines to roll out,” he says. “It will need some investment to buy and distribute them.” An effective vaccine may be on the way, but ensuring that it reaches those who need it the most will not be easy.