Real-World Potential Seen in Promising Candidate for Whole-Sporozoite Malaria Vaccine

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A report in Science Translational Medicine found that an experimental malaria vaccine containing whole inactivated Plasmodium Falciparumsporozoites decreased the risk of infection in adults living in a malaria endemic area.

In a 5-dose regimen with a lower concentration, the vaccine had previously shown greater than 90 percent vaccine efficacy in controlled infections and 52 percent vaccine efficacy in natural infections. In a Burkina Faso region with high transmission, the current study tested an ten-fold higher concentration of vaccine against natural infection. The regimen used 3 doses rather than 5, as it was considered to be more realistic in real-world situations.

The authors reported that at the prespecified endpoint, 24 weeks after the third dose of the vaccine, 36% of the 39 participants who had been vaccinated tested positive for malaria, compared to 58% of the 40 participants who were given a placebo. This translates into a statistically significant efficacy of the vaccine of 38%.

The authors note that the standard method for measuring the efficacy of malaria vaccines is to consider the time delay between vaccination and infection. This resulted in a 48% efficacy. This result was not statistically significant. The report states that 76 weeks later, 77% (of the vaccinated group) tested positive for malaria, compared to 85% (of the placebo group). This resulted in an efficacy of 46% using the standard method.

The authors discovered that the antibody response tests 2 weeks after receiving the last dose of vaccine were higher in participants who received vaccinations than those in placebo groups. After 24 weeks, the antibody levels of vaccinated individuals who had not been infected by malaria were higher than those infected.

The authors concluded that “this 3-dose regimen is easy to administer and well tolerated. It does not pose any serious safety concerns which would prevent further development.”

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