High dosages of trial malaria vaccine produce promising results

New trial vaccine against malaria shows promise (Image: CDC/Jim Gathany)

A vaccine against malaria currently being developed in the US offers new hope to fight the infectious disease that enters the body through a mosquito bite. According to the World Health Organization, malaria killed 660,000 people in 2010. The intravenous vaccine currently being developed by Sanaria and the National Institute of Allergy and Infectious Diseases (NIAID) has produced promising results in volunteers who received a high dose the vaccine.

The PfSPZ Vaccine uses a weakened version of Plasmodium falciparum, which the researchers say is the most deadly strand of the malaria-causing parasites. Phase I included tests in 57 healthy adult volunteers aged between 18 and 45 years who had never been infected with malaria. They were then split into groups that received different, increasing dosages of the vaccine (two to six). A seven-day monitoring period followed and no adverse effects associated with the vaccine occurred, NIAID said in a press release.

Blood tests revealed that participants who had received a higher total dosage of PfSPZ Vaccine produced more antibodies against malaria and more vaccine-specific immune system cells (T cells). Three weeks after participants had received their final vaccine dose, those volunteers as well as a group who didn’t get the vaccine, were exposed to bites by five mosquitoes carrying the P. falciparum strain. They were monitored as outpatients for seven days and then admitted to the NIH Clinical Center.

The results showed promise for the vaccine as the vast majority, 12 out of 15, of those who received higher dosages of vaccine were not infected. In contrast, 16 out of 17 participants in the lower dosage group became infected and 11 out of 12 of those who received no vaccine also became infected after being bitten by the mosquitoes. Those who were diagnosed with malaria were given anti-malarial drugs to get rid of the infection.

One of the challenges faced by the researchers now is figuring out a way to make the vaccine administrable into or under the skin. The trial was conducted with an intravenous version of the vaccine, which has proven to be more effective in producing a strong immune response.

The researchers plan on assessing whether higher doses administered this way would produce the same protective results as found in the study. They also plan on testing the vaccine against other parasite strains of the Plasmodium family, and find out more about how long protection lasts.

“Scientists and health care providers have made significant gains in characterizing, treating and preventing malaria; however, a vaccine has remained an elusive goal,” said NIAID Director Anthony Fauci. “We are encouraged by this important step forward.”

WHO says that malaria mortality rates have been decreasing since 2000, down by 25 percent globally and by 33 percent in the WHO African region. Children are the most common victims of the disease and it is estimated that a child dies every minute from the disease.

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