More than 19,000 children were enrolled in trials to prove the world’s most advanced malaria vaccine candidate. Mary Okeyo's son was one of them. “I would like all children to be able to get the vaccine,” Mary says. Photo: PATH/Eric Becker.
With one promising vaccine in the works, PATH is building tools to develop more candidates more quickly
Although many people thought it was impossible to develop a vaccine against a human parasite, PATH and our partners are close. After decades of research and testing, and dozens of clinical trials involving more than 19,000 children, the world’s most advanced malaria vaccine candidate, RTS,S (Mosquirix™), received a thumbs-up from European regulators in July 2015.
PATH joined the RTS,S effort in 2001 to accelerate the vaccine’s development by helping to overcome funding challenges and advance clinical development of the vaccine for young children in Africa. Our Malaria Vaccine Initiative (MVI) brought resources and field expertise to the table with vaccine developer GlaxoSmithKline, in a collaboration that grew to include scientists from across Africa, Europe, and North America.
The phase 3 efficacy and safety trial of RTS,S was the largest malaria vaccine trial ever. With our partners, we helped to upgrade facilities at some of the 11 trial sites in 7 countries, train researchers to run the trial to the highest international standards, and enroll 15,459 children in a trial that lasted more than four years.
The vaccine reduced the number of malaria cases by half in children and by one third in infants over the first year after vaccination. Vaccine efficacy waned over time and was enhanced by a fourth dose given 18 months after the initial series. Modeling indicates that—if rolled out correctly and used alongside current interventions—RTS,S could prevent millions of malaria cases, a potentially important public health impact given the tens of millions of cases of malaria among children in Africa every year.
Contributing to malaria elimination by accelerating the development of vaccines
Scientists at the Kenya Medical Research Institute in Kisumu took part in the clinical trials of the vaccine candidate RTS,S—helping to advance one of our malaria vaccine candidates. Photo: PATH/Eric Becker.
PATH is committed to eliminating malaria in individual countries and ultimately to its eradication worldwide. Doing so will require a spectrum of tools and strategies, and we believe that vaccines are an important addition to the toolkit.
MVI has one of the largest portfolios of malaria vaccine candidates and approaches in the world. Some build on progress made with RTS,S—as a first-generation vaccine targeting disease—while others pursue different paths for eliminating and eventually eradicating the disease.
We’re pursuing this multipronged approach because developing a malaria vaccine poses unusual challenges. For one thing, a successful vaccine must defeat a parasite that has co-evolved with humans for millennia and is a master of adaptability. The parasite primarily targeted by MVI’s efforts is Plasmodium falciparum, the deadliest of malaria parasites affecting humans and the one most prevalent in sub-Saharan Africa.
MVI focuses primarily on two priority areas for vaccine development: anti-infection vaccines (AIVs) and transmission-blocking vaccines (TBVs). AIVs (of which RTS,S is an example) are meant to prevent infection in people bitten by infected mosquitoes. TBVs aim to help eliminate malaria by ending the cycle of transmission between humans and mosquitos and back again. This type of vaccine prevents the mosquito that bites a malaria-infected person from getting infected, thus stopping the parasite’s life cycle in its tracks.
Unlocking the secrets of immunity
Methods to consistently evaluate vaccine candidates are crucial to success. PATH supports the development of evaluation technologies, including laboratory tools that yield consistent results. These tools let scientists know early on whether an approach prompts the human immune system to resist the malaria parasite or (in the case of a TBV) if it blocks transmission of parasites through the mosquito.
Evaluation technologies can provide researchers with the information they need to decide whether to move a particular vaccine project into the next stage of testing, including testing in regions that suffer from malaria.
In it for the long haul
At PATH, we are tenacious about overcoming hurdles to success. Until we have a vaccine that effectively accelerates malaria elimination and is available for use by those who need it most, we will not give up.
In communities across Africa, hopes are high. Scores of parents who live near the Kombewa research facility in Kenya chose to enroll their children in the clinical trials for RTS,S.
Three of Mary Okeyo’s neighbors lost children to malaria, so she was eager to enroll her six-month-old son. “I worry about malaria,” she said. “I would like all children to be able to get the vaccine.”