Malaria, a potentially deadly mosquito-borne infection, remains a problem in many parts of the world. Reducing infections has been challenging because no vaccine is currently available. Prevention efforts have mostly concentrated on eliminating the transmission vector, mosquitoes. A recent study published in Nature shows that a new vaccine for malaria is well tolerated by humans and can provide significant immunity to malaria.

Malaria is caused by infection of the protozoan parasite Plasmodium falciparum. These are complex cells that have a number of means to evade the immune system, which has made the creation of vaccines challenging. To make this new vaccine, the parasites were first rendered harmless via radiation and then rapidly frozen for preservation. Healthy adult volunteers were given three doses of this vaccine at 28-day intervals before being challenged with exposure to the malaria parasite. Under these conditions, nine out of the nine immunized participants avoided a malaria infection.

Additionally, subjects who received non-optimized concentrations of the vaccine dose still exhibited some protection against infection, with one-third or two-thirds of vaccinated people demonstrating immunity, depending on the dose.

This vaccine is considered safe and was well tolerated by all participants. In the whole study, there were no serious adverse consequences to vaccination. In fact, the frequency of adverse events was the same for people who received the vaccine and people who received a placebo.

When researchers examined the blood of vaccinated individuals, they found a dose-response of antibodies against the malarial parasite, which was expected given the vaccination mechanism. The authors hypothesized that immunization worked because the immune system eliminated parasite-infected liver cells during the parasite’s five-to-six day maturation period. In typical malaria infections, the parasites can stick to liver cells during this time, but later spread throughout the body; this did not occur in immunized participants.

The schedule for inoculation with this vaccine requires participants to be given three doses at twenty-eight day intervals. If this could be optimized for a shorter inoculation schedule, it would be easier to administer in regions with endemic malaria. However, two thirds of participants were immune when they were given three doses at five day intervals, which suggests that some shorter immunization schedules could be effective.

Though this study shows promising first steps in terms of immunization against malaria, this clinical trial was extremely small, with only nine volunteers in the group that showed full immunity. The authors of this study are also planning future work that will determine how long vaccine recipients remain immune to malaria.

This isn’t the only progress that’s been reported on malaria vaccines. This week, a paper in PNAS describes a vaccine based on weakened versions of the malarial parasite. That involved another small trial, and the vaccine wasn’t quite as effective as this, protecting only about two-thirds of those who received it. But the trial showed that it was effective against additional strains of the parasite.

We may finally be on the verge of progress against a disease that has resisted eradication efforts for decades.

Nature, 2017. DOI: 10.1038/nature21060 (About DOIs)