The search for an effective malaria vaccine may soon be over, as a treatment designed to mimic the immunity-conferring effects of a treated mosquito bite provided up to 100% protection for a 10-week period in a recent clinical trial detailed earlier this week in the journal Nature.
More than 200 million people are infected with malaria each year, according to Popular Science, and symptoms include fever, chills, headache, vomiting and possibly death. While measures that were designed to reduce the chances of being bitten by infected mosquitoes have been successful to some degree, a true vaccine for the life-threatening disease has remained out of reach.
Now, however, scientists at the Institute of Tropical Medicine, the German Center for Infection Research (DZIF) and biotech firm Sanaria believe that they have developed a vaccine using fully viable malaria pathogens instead of weakened or inactive ones that could solve the problem.
“We’ve known as scientists that you could immunize with the bite of a radiated infected mosquito since the 1970s,” Sanaria chief executive and science officer Stephen Hoffman told Popular Science. Likewise doctors have known since 2009 that mosquito bites treated with an antiviral called chloroquine also confers immunity – but, Hoffman pointed out, “you can’t take mosquitoes to your doctor’s office and let them bite you.”
Part of the problem is the fact that malaria is caused by a parasite, not a virus or bacteria, but in earlier studies, researchers found that something in the sporozoite stage of the parasite’s lifecycle – the period of time in which malaria can infect humans – could confer potential immunity to the pathogen. Theoretically, doctors knew that they could use this trick to create a vaccine.
Vaccine performed worse, but was still effective, in the real world
The issue, Hoffman told Popular Science, is that the parasite has at least 5,000 genes, making it next to impossible to determine which of those were key in conferring immunity. So instead, he and his colleagues came up with a way to extract the sporozoites, make it so that they were safe to humans, then injecting them into patients to trigger a reaction from the immune system.
Known as PfSPZ-CVac, the candidate drug was up to 100% effective during a clinical trial held in Germany, but slightly less effective during a real-world test in Mali, according to AFP reports. In a statement, the study authors said that in one test, nine subjects who never had malaria were completely protected from the disease after receiving the highest dose of the vaccine three times (once every four weeks).
In the Mali test, however, 44 people were given five doses of the drug and were found to have a lower infection rate than their non-vaccinated counterparts over a six-month span. Among those who were vaccinated, 66% per infected, while 93% of the control group – those who were given a placebo or dummy injection, contracted the disease, the news agency said. Hoffman called that “the highest level of protection ever seen with a malaria vaccine… in a real setting.”
According to the authors, the immunity was likely due to specific T-lymphocytes and antibody responses to the parasites in the liver. They studied the immune reactions of the patients’ bodies and identified protein patterns which they say will allow them to further improve on the vaccine, which Hoffman warns is still a long way from being readily available and usable.
“This is the first step. We still have a lot of work cut out for us,” he told Popular Science. “But we believe that this kind of approach can be used to immunize the entire population, so we can halt transmission of the parasite and eliminate it geographically from systematically defined areas.”
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