RTS,S/AS01 is a Malaria vaccine candidate; a recent study published in the New England Journal of Medicine has shown this vaccine could not establish long-term efficacy against clinical Malaria.
Malaria is an infectious disease caused by a parasitic protozoan (a group of single-celled microorganisms) belonging to Plasmodium types. It is a transmitted between affected patients and healthy subject by mosquito named Anopheles.
Malaria causes a spectrum of mild to severe symptoms; they can vary from fever, fatigue, headache in mild cases, to symptoms like yellow discoloration of the skin, coma and even death in severe cases. The symptoms typically begin after 10 to 15 days of being bitten by the mosquito. Malaria is mostly prevalent in tropical and subtropical areas like Sub-Saharan Africa, Asia, and Latin America.
Based on a report from WHO (World Health Organization), in 2015, there were 214 million cases of malaria worldwide. This resulted in an estimated 438,000 deaths. Keeping this dramatic rate of infection and death in mind necessitates establishing effective prevention methods.
Currently, the main tools of malaria prevention are: insect nets and repellents, insecticides and antimalarial agents for those traveling to places with high malaria prevalence. All of these methods have limitations and varying efficacies, thus researches are looking for developing an effective vaccine.
A new article, which is published in the New England Journal of Medicine, reflects the results of a clinical trial about the efficacy of RTS,S/AS01 Malaria vaccine, a phase-3 approved malaria vaccine. The study was conducted in Kilifi, Kenya, and Korogwe, Tanzania. The investigators enrolled a total of 447 African children into the study; the participant children were in the age range of 6 to 17 months. The study population was then randomly assigned into two statistically similar groups of study and control.
The subjects in the study group were administered the RTS,S/AS01 vaccine and those in the control group received Rabies vaccine (for control). They were followed up for clinical and laboratory signs of malaria for a total of 7 years. Finally, the rates of protection against malaria infection were compared between the two groups.
The investigators have reported an efficient protection of the RTS,S/AS01 vaccine against malaria infection at the end of the 1st year, but this protection subsequently waned over time, to zero in the 4th year and even to negative rates at the 5th year in areas with high malaria exposure. This means that at the end of the 5th year, children who had received the RTS,S/AS01 vaccine were even more prone to malarial infections than children who had not received this vaccine.
The results of this study are somehow different than the results of previous studies, which had shown an acceptable efficacy of RTS,S/AS01 vaccine. The authors attribute this variability in results to the different sizes of the study populations and also to those cases that did not complete a follow-up.
Written By: Nima Makhdami, M.D.