Researchers found the PfSPZ vaccine protected healthy adults against malaria for more than a year.

Published the journal Nature Medicine, the results from a phase I clinical trial reveal that a vaccine called PfSPZ protected healthy adults against malaria for more than 1 year.

Malaria is a disease most commonly transmitted through the bite of an infected Anopheles mosquito.

Symptoms of malaria include fever, flu-like illness, headache, shaking chills, muscle aches, and nausea and vomiting. It can also causeanemia, jaundice, and - if not treated promptly - seizures, kidney failure, coma, mental confusion, and death.

According to the World Health Organization (WHO), there were around214 million cases of malaria across the globe last year and around 438,000 deaths from the disease.

Plasmodium falciparum is the malaria parasite most likely to cause severe, life-threatening disease.

In the new study, principal investigator Dr. Robert A. Seder, of the National Institute of Allergy and Infectious Diseases (NIAID) Vaccine Research Center, and colleagues reveal how the PfSPZ vaccine achieves long-term protection against P. falciparum.

PfSPZ vaccine: Assessing long-term protection against malaria

The PfSPZ vaccine consists of live, weakened P. falciparum sporozoites, which are immature forms of the parasite.

In previous research, Dr. Seder and colleagues found that the vaccine was highly protective against P. falciparum for 3 weeks following immunization.

For this latest research, the team set out to investigate whether the vaccine would offer longer-term protection.

The researchers gave the vaccine to 59 healthy adults aged 18-45 years with no history of malaria. A further 32 healthy, age-matched adults without a history of malaria were enrolled but were not vaccinated, serving as controls.

The team divided the vaccine recipients into groups in order to determine the optimal dosage, number of vaccinations, and administration route for the most effective protection.

Some of the vaccinated participants received three intravenous (IV) immunizations, while others received four IV immunizations - all at higher doses than had been previously tested in humans.

Some of the vaccinated participants received four immunizations through intramuscular injection (IM) at a dose tenfold higher than the IV dose.

IV administration more effective than IM

The team assessed both short- and long-term protection against malaria in this study.

In order to assess short-term protection, all participants were exposed to the bites of mosquitoes infected with P. falciparum 3 weeks after their last immunization.

On assessing the blood samples of participants, the researchers found that three of nine subjects who received three IV doses of the PfSPZ vaccine had no detectable parasites in their blood, meaning they were protected against malaria.

Of nine participants who received four IV doses of the vaccine, seven were found to be protected against P. falciparum, while only three of eight subjects who received four IM doses were protected.

This suggests that IV administration offers better protection at a lower dose than IM administration.

Malaria vaccine offered 1-year protection for 55 percent of participants

The researchers enrolled an additional group of 11 participants in order to assess long-term protection of the PfSPZ vaccine.

These participants received four IV doses of the vaccine, and they were exposed to the bites of P. falciparum-infected mosquitoes 21 weeks after their last vaccination.

The researchers found that six of these 11 participants - 55 percent - had no detectable parasites in their blood following exposure to the parasite.

Four of these subjects - as well as one participant who received four IV doses of the vaccine and had no detectable P. falciparum in the blood following exposure at 3 and 21 weeks - were then further exposed to bites of infected mosquitoes at 59 weeks after their last vaccination.

None of these five participants developed P. falciparum in their blood, while all unvaccinated control subjects did.

All in all, the researchers conclude that the PfSPZ vaccine protected 55 percent of healthy participants against malaria for over 1 year.

What is more, the team found that the vaccine appeared to provide sterile protection against malaria in these individuals, which means they are not only protected against the disease, but they are also unable to transmit it.

"It is now clear that administering the PfSPZ Vaccine intravenously confers long-term, sterile protection in a small number of participants, which has not been achieved with other current vaccine approaches," notes Dr. Seder.

Additionally, the researchers say the vaccine was well tolerated by participants, and no serious adverse events from the vaccine were identified.