Sanaria’s malaria vaccine posted another positive clinical result as it provided significant protection for many healthy adults in a phase 1 study carried out in Mali, but a notable gap compared with results from U.S. studies calls for scientists to further improve the formulation.

The recent study tested Sanaria’s PfSPZ vaccine on 93 healthy African men and nonpregnant women ages 18 to 35. The intravenous vaccine, which contains a live but weakened malaria parasite to generate an immune response, aims to protect people against infection with Plasmodium falciparum malaria—the deadliest form of the disease.

As results published in the Lancet Infectious Diseases show, 93% of those who received placebo developed malaria infections during the following transmission season, compared to 66% of participants in the five-dose vaccine arm. 

Sanaria CEO Stephen Hoffman described the results in a statement (PDF) as "extremely encouraging," especially given that the company knew the current regimen is "suboptimal." 

"We feel that we are moving rapidly toward establishing a dosage regimen that will provide the high level protection needed by the billions of people at risk every day from this lethal disease," he said.

Co-principal investigator Sara Healy noted in a statement that researchers have not documented that level of protection from previous studies in Africa in areas with "an intense transmission season." 

But at 48% protective efficacy by time-to-event analysis and 29% efficacy by proportional analysis, the results don't quite measure up to those from U.S. studies. In one trial that lasted about a year, the shot protected 55% of healthy U.S. adults who had no prior malaria infection. In another, it protected 57% of subjects 24 weeks after the final dose.

Researchers only consider a malaria vaccine to be suitable for mass vaccination programs in malaria-epidemic areas when it can protect at least 80% of recipients throughout the transmission season.

The same clinical team in Mali just completed a follow-up study examining a three-dose regimen with higher dosage levels. Readouts are expected in mid-2017 and another phase 1/2 trial is currently recruiting infants and children ages 5 months to 9 years in Kenya.

Rockville, Maryland-based Sanaria secured an FDA fast-track designation for PfSPZ last September. In addition to support from the NIH, it has $48.5 million in financial assistance from the government of Equatorial Guinea and energy companies with operations in malaria-endemic areas.

With success, the company could eventually look to challenge vaccine giant GlaxoSmithKline, which won the world's first malaria vaccine approval back in 2015. Since then, however, the London-based pharma giant has had its global Mosquirix launch stymied by a WHO recommendation that the vaccine be tested in local pilot programs.