Oh, mosquitoes!  Everybody hates them.  They buzz, they bite, they itch, and they’ve ruined as many picnics as those pesky ants have.  Mosquitoes are much worse than a mere nuisance, however.  They carry a parasite that can infect a person with malaria, a disease that kills close to a million people around the world every year and makes another two million people sick from the disease.  And as the global climate warms, those parasite-infested mosquitoes, and malaria, are spreading.

Medical science has long sought a vaccine against the Plasmodium falciparum, a parasite that causes malaria, but such a vaccine has remained elusive.  On Monday, however, the ‘New England Journal of Medicine’ published a report from the Bill and Melinda Gates Foundation that says its researchers, led by deputy director of vaccines and infectious diseases, Dr. W. Ripley Ballou, have identified a vaccine that cut the rate of illness by half and is safe and effective when given alongside other childhood vaccinations.  According to the World Health Organization, most people dying from malaria are younger than five years old.

Calling the vaccine RTS,S, research has focused on sub-Sarahan Africa, where the prevalence of malaria is extreme.  The first study compared the vaccine against a control group of children, from five to 17 months of age, in Kenya and Tanzania, who got rabies vaccinations instead of RTS,S.  The study involved a total of 894 children.  Children getting RTS,S experienced 38 malarial episodes while those getting the rabies vaccine experienced 86 such events, representing a drop in infection by as much as 53%.

A second study in Tanzania involved 340 infants who were given the RTS,S vaccine along with other common childhood vaccines at 8 weeks of age and again at 12 and 16 weeks.  Adding RTS,S to the other vaccines did not produce any adverse effects nor did it diminish the effectiveness of the other vaccines, which inoculated the children against diptheria, polio, pertussis (whooping cough), and Haemophilus influenza B.  The infants getting the malaria vaccine developed 65% fewer malarial infections than the infants in the control group who didn’t get the RTS,S vaccine.

Further study is ongoing, with tests for safety and efficacy being done on 16,000 infants reporting to 11 African sites, all locales with differing rates of infection and mosquito activity.  A second aspect of these trials is to determine how long the vaccine remains effective.  Previous studies indicated a window of immunity that lasted about 18 months but a soon-to-be-published report indicates a much longer period of immunity.

Malaria occurs in tropical zones throughout the world, where about half of all people live.  Eradicated in the United States and Europe about 50 years ago and mostly forgotten in these regions, attention was once again called to the disease about ten years ago, when high-profile entities, such as the Gates Foundation, and Bono, singer for the rock band, U2, became involved.

Since then, the death rate from malaria has dropped by about half in Ethiopia, Rwanda, and Zambia, thanks in part to newly developed medicines that combat the disease and the widespread distribution of bed nets laced with insecticide that repel mosquitoes.  While progress is evident, concerns that the parasites which cause the disease would eventually develop resistance to the medicines and/or the insecticides has kept the search for a vaccine ongoing.

Malaria occurs when a parasite-infested mosquito bites a person, who feels fine for about a week as the parasite travels through the bloodstream to the liver, where it reproduces.  The new colony of parasites then reenters the bloodstream, where they invade red blood cells and replicate at a rate of 10 times in a 48-hour period.  This replication process causes the red blood cell to burst, releasing these new parasites, which further spread infection.  The RTS,S vaccine targets the parasite while it is still in the liver.

The pharmaceutical company GlaxoSmithKline Biologicals, of Belgium, developed the RTS,S vaccine, along with support from the nonprofit consortium, PATH Malaria Vaccine Initiative, which works collaboratively with drug companies all around the world.  The current target date for licensure is 2011, which would make the vaccine available for use as early as 2012.