In 1897, British doctor Sir Ronald Ross discovered that malaria in people is transmitted to and from mosquitoes. Dr. Ross went on to win the Nobel Prize for his discovery, and since then, mosquitoes have been enemy number one when it comes to defeating a disease that takes a life every single minute—most of them young children in sub-Saharan Africa.
Since then, the malaria community has continued to innovate and improve methods to control the disease. In the vaccine field, the community has begun to focus on approaching malaria in a surprising new way: with a vaccine to protect malaria-transmitting mosquitoes. Put another way, such a vaccine would stop humans from giving malaria-causing parasites to mosquitoes.
Why protect mosquitoes from humans?
It helps to understand the vicious cycle of malaria, which works like this: a mosquito bites a child and transmits the malaria parasite, perhaps causing the child to get very sick. A week later, if a non-infected mosquito feeds on the same child, it is the child who passes the parasite to the mosquito. Soon, that mosquito may bite the child’s father, passing the parasite to him. Even if he shows no symptoms of malaria and doesn’t get sick, he can still pass parasites on to another mosquito. And the cycle goes on.
That’s where a vaccine comes in.
A transmission-blocking vaccine (TBV) could break the never-ending and often deadly cycle. This type of vaccine could prevent the mosquito that bites the malaria-infected person from getting infected. If the mosquito does not get infected, it cannot give malaria to another person.
From polio to smallpox, we think of vaccines as preventing people—not mosquitoes—from getting a disease or from getting sick. This type of vaccine would not protect someone bitten by an infected mosquito from getting malaria or lessen its symptoms; it would help protect that person’s family and community. And if almost everyone in a community received such a vaccine, the entire community would benefit by having fewer and fewer infected mosquitoes and, therefore, fewer malaria cases over time.
Creating "community immunity"
Ultimately, the transmission-blocking approach would create “community immunity” and would have the potential to eliminate malaria altogether from the affected areas. This approach for the greater good—rather than for immediate, personal protection—could mean eradication of malaria in the long term.
While the malaria community has made extraordinary progress over the last decade in reducing malaria deaths, the wily malaria parasite is rapidly becoming resistant to some of the best tools—drugs, and insecticide sprays. Another tool to break the cycle of transmission could help tip the balance against malaria, and history tells us that a disease is unlikely to be eradicated without a vaccine.
To reach the end game, it would be important to have a suite of new tools—including a vaccine—that work together.
There are a number of potential transmission-blocking vaccines in early development, and MVI is working with partners to research these vaccine approaches. In collaboration with Fraunhofer USA, MVI has advanced a transmission-blocking vaccine candidate through early-stage clinical trials, and the National Institutes of Health is also testing at least one vaccine approach in early-stage trials. The Malaria Vaccine Technology Roadmap, updated by the international community in 2013, has called for vaccines that reduce transmission by the year 2030.
Should a transmission-blocking vaccine become a reality, it would be another critical tool that paves the way for eliminating and eradicating malaria.
Ashley Birkett is Director of the PATH Malaria Vaccine Initiative. A version of this article appeared as a blog post in the Guardian.