The quest for a vaccine that provides lasting protection against malaria took another step forward today with the release of study results showing a candidate made from a weakened version of the parasite that causes the disease offered protection to five trial participants more than a year after it was administered. The results, while still limited, represent the continued advance of an approach that scientists at the National Institute of Allergy and Infectious Disease first noted promise in nearly five years ago.
NIAID scientists saw potential for the candidate in 2011, after studies using animal subjects indicated it could be more effective than it had been in earlier human trials if injected directly into the bloodstream. Delivering the vaccine intravenously, they reasoned, would prompt a stronger and more immediate protection, than an injection under the skin against the parasite in the liver, its first stop after a person is infected through a mosquito bite. At the same time, researchers saw the possibility that the administration of an intravenous vaccine could be challenging in settings with limited health resources, and among small children. Vaccines injected into a muscle were more protective, they noted, than those injected under the skin.
The trial described today in Nature Medicine, enrolled 101 adults, 59 of whom received the vaccine candidate, and 32 of whom did not. Participants received two dosages, one stronger than the other, administered among a small group three times and among the rest four times, with most participants receiving the vaccination intravenously and the rest receiving a dosage 10-times higher than the stronger dosage used in the intravenous administration, injected into a muscle. The greatest protection, they found, was conferred by the stronger and more frequent intravenous administration. Researchers then vaccinated a group of 11 previously unexposed participants with four intravenous doses. Five of those participants, after repeated exposures, the last 59 weeks after vaccination, remained malaria-free. That result, researchers led by Andrew S. Ishizuka of the Vaccine Research Center at NIAID, wrote, signals a possibility that lasting protection from malaria can be achieved through a vaccine. The article also notes that completed studies have provided some data on the feasibility of intravenous vaccinations among adults in three southern African countries, while studies currently underway are exploring the safety and possibilities of intravenously administered injections among young children and infants.
Researchers now plan to discover if additional dosages will increase the strength and duration of protection, including from natural exposure and among all age groups.
While malaria incidence and deaths have dropped sharply over the last decade and a half, last year about 214 people required treatment for the disease, nearly half a million died from it and, according to the World Health Organization, more than 3 billion people remain at risk for the disease. The disease takes its greatest toll in sub-Saharan Africa, and among children younger than 5 years old.