A new type of malaria vaccine is showing promise in early studies.
The vaccine combines live malaria parasites and antimalarial drugs to produce immunity without causing disease. If larger-scale trials continue to show success, the vaccine could eventually help to reduce the 200 million-plus malaria cases recorded every year.
Malaria, a disease caused by parasites that are spread by mosquitoes, kills over 400,000 people a year. Although the World Health Organization estimates that almost half the world's population is at risk of contracting malaria, most cases and deaths occur in sub-Saharan Africa and in children under age 5. The symptoms associated with malaria are typically flu-like and, if left untreated, can lead to organ failure and death.
Despite the facts that the disease is treatable with drugs and preventable with insecticide-treated bed nets, the decline of cases has stalled in the past few years. One vaccine with limited effectiveness is undergoing a pilot program while another is in later-stage trials, but none is in widespread use yet.
"Malaria has been a really tricky infection to make a vaccine against," said Alexis Kaushansky, a malaria researcher at the University of Washington and Seattle Children's Research Institute who was not involved in the new study. "I think this vaccine is really exciting and promising."
'A game changer'
Earlier studies have shown that people can develop immunity to malaria, but it requires exposure to many more parasites than mosquito bites deliver.
The new vaccine, developed by biotechnology company Sanaria, involves directly injecting large doses of parasites and administering antimalarial drugs to prevent patients from getting sick.
Mass producing enough parasites for a vaccine is a challenge, however. Over many years, Sanaria developed a process to grow, feed and extract parasites from large numbers of mosquitoes at its facility.
Sanaria's manufacturing process has made it possible to test this type of vaccine made of live, purified parasites, said Patrick Duffy, an internal medicine physician at the National Institute of Allergy and Infectious Diseases and a co-author of the study. "That's been a game changer."
In the latest clinical trial on a small number of volunteers, at least 77.8% of the participants who received the vaccine with chloroquine or pyrimethamine were protected against infections three months later.
"We were pretty amazed at the protection," Duffy said.
The vaccine also protected participants from both the African strain of the parasite used to make the vaccine and a different South American strain. These results mean that the vaccine could potentially provide broad protection beyond just a single strain or even similar strains of malaria parasites, according to the authors.
"That's really different than what previous trials have shown, so that's super encouraging," added Kaushansky.
Another malaria vaccine known as RTS,S, or Mosquirix, is undergoing a large-scale pilot program in Ghana, Kenya and Malawi. Previous clinical trials showed that RTS,S prevented about 39% of cases of malaria in young children in several sub-Saharan African countries over four years.
Another vaccine by the University of Oxford, R21, is also starting larger-scale trials after early studies showed the vaccine to be up to 77% effective.
Both RTS,S and R21 rely on administering a protein that's part of the parasite to build up a person's immunity rather than the whole, live parasites that the Sanaria vaccine in this study uses.
The Sanaria vaccine has started the second of three stages of clinical trials in Mali, where malaria is the leading cause of disease and death.
While she is hopeful, Kaushansky said that the process of harvesting parasites from mosquitoes may encounter hurdles when scaling up manufacturing. Malaria vaccines also often run into challenges when switching from early, carefully controlled trials with participants who have never had malaria before to populations that have already experienced high rates of malaria.
"I think we're all excited to see how the next round of trials play out and to see if it will protect people who are highest at risk," Kaushansky said.