WASHINGTON: An experimental vaccine against malaria known as Mosquirix or RTS, that weakens over time and is only about four percent effective over a seven-year span, researchers said on Wednesday.
The findings, published in the New England Journal of Medicine, are based on a phase II clinical trial involving more than 400 young children in Kenya.
There is currently no vaccine against malaria in the world market and Mosquirix, which is developed by the British pharmaceutical giant, GlaxoSmithKline, is the experimental vaccine in the most advanced stage of development.
It has also been tested in a vast clinical trial that spanned seven African nations, and last year the European Medicines Agency gave it a “positive scientific opinion” regarding its use outside the European Union (EU).
The current study, involving 447 children from five to 17 months of age, suggested that some of the infants were given three doses of the malaria vaccine, while others received a vaccine against rabies for comparison.
In the first year, the protection against malaria among Mosquirix vaccinated children was 35.9 percent but after four years, this protection fell to 2.5 percent. The researchers said that on average, over the course of seven years, the vaccine would be considered just 4.4 percent effective against malaria.
According to study, this rate was substantially lower than that seen over short-term follow up.” Furthermore, among children who were more frequently exposed to mosquito-borne malaria, cases of infection with the parasite P falciparum in the fifth year were higher than in the control group.
The researchers said that this phenomenon may be occurring because the vaccine protects against the earliest form of malaria’s life cycle, known as sporozoites, and reduces exposure to a later form, known as the blood-stage parasite, which causes the clinical symptoms of malaria such as fever, nausea, vomiting and diarrhea.
The study said, “The reduced exposure to blood-stage parasites among persons who have received the RTS, S/AS01 vaccine may lead to a slower acquisition of immunity to blood-stage parasites, leading to an increase in episodes of clinical malaria in later life.”
The results of a larger, phase III clinical trial with the same vaccine, published last year, showed that three doses could reduce the risk of malaria by 28 percent over a period of four years.
