Sometimes science moves painfully slowly, and then it all seems to happen at once. In the space of a week, two successful trials have been announced for different malaria vaccines. We are still some way from a solution to a disease that infects more than 200 million people a year, killing 400,000, but we're getting closer.
Last Wednesday, Dr Benjamin Mordmueller and Professor Peter Kremsner of the University of Tübingen, Germany announced in Nature that the PfSPZ-CVac vaccine had proven 100 percent effective on nine healthy adults who were given the maximum dose of the vaccine. Some of the 58 people given smaller doses also developed immunity.
Participants were injected with the vaccine, followed by a dose of chloroquine to prevent disease. Ten weeks later those given the full dose were still showing immune responses considered sufficient to prevent malaria infection.
PfSPZ-CVac differs from previous attempts at malaria vaccines by using fully viable malaria pathogens. Previous attempts used attenuated pathogens or specific molecules from the parasite in the hope the immune system will learn to attack these, and when exposed to a live parasite will be able to kill it off. Sadly, success has been limited.
"By vaccinating with a live, fully active pathogen, it seems clear that we were able to set off a very strong immune response," Mordmueller said in a statement. "That protection was probably caused by specific T-lymphocytes and antibody responses to the parasites in the liver,” Kremsner added.
PfSPZ-CVac will now be tested in Gabon to determine whether the protection lasts.
Today the Proceedings of the National Academies of Science has published a trial led by Dr Robert Seder of the National Institutes of Health, Bethesda, using an attenuated parasite, one that has been weakened so as not to make the recipient sick. Nine of 14 people given the vaccine proved resistant to the same strain of the parasite 19 weeks later.
A success rate of 64 percent might seem a poor return compared to PfSPZ-CVac's 100 percent. On the other hand, attenuated pathogens are safer than full strength parasite doses. Moreover, Seder's work provided some subjects with protection not just against the strain of malaria against which they were vaccinated, but other strains as well. As the paper notes; “Protection against genetically diverse strains is urgently needed,” since providing separate vaccines against each strain would be very expensive.
The authors conclude that their vaccine “primes antigenically diverse T-cell responses” in ways vaccines made from subunits of the parasite do not.
Both projects have a long way to go before they are ready for mass production. Many promising vaccines have failed at the later hurdles, so it's just as well there's progress on more than one path.