Sometimes a vaccine is a slam dunk. Take, for example, the 97.5 percent Ebola vaccine or the 97 percent measles vaccine. Another time, a vaccine is a fool, but with little to no protection and clearly intended for the dustbin.
Then there is a third group: the vaccines that fall in the middle. They could protect some, but far from everyone. The fate of these vaccines is less certain – indeed an open question.
This is the case of the world's first malaria vaccine, which was carefully added on Tuesday, April 23, to routine vaccinations in African Malawi as part of a pilot program. Ghana and Kenya will also introduce the vaccine in the coming weeks.
The vaccine, known as RTS, S, is only effective at about 39 percent to prevent malaria – and only in children receiving four separate doses. It is only 29 percent effective to prevent the most severe forms of mosquito-borne disease.
With more than 200 million malaria cases worldwide and 435,000 deaths, even modest efficacy can cause tens of thousands of rescued lives.
"This is a milestone," Kate O'Brien told reporters at a news conference on Tuesday. She is the director of the Department of Immunization, Vaccines and Biology of the World Health Organization. RTS, S is a "vaccine of the first," she added. It is the first malaria vaccine to show such efficacy after decades of research and dozens of other candidates. It is also the first to reach young, vulnerable children with a routine inoculation program.
RTS, S has been working for over 30 years. It was founded in 1987 by GlaxoSmithKline and contains a fragment of a protein of the malaria parasite Plasmodium falciparum . This fragment invites the immune system to attack after a mosquito has first carried the parasite into the bloodstream and before the parasite can infect the liver. It may ripen, spawn, reappear to infect red blood cells and cause disease symptoms.
From 2009 to 2014, researchers tested RTS, S in a Phase III clinical trial in seven African countries, where 250,000 children die each year from parasitic infection. Data from nearly 15,500 infants and children in the study showed that the vaccine is only about 39 percent effective. It remains to be seen whether this rate of impact will be maintained in practice or not.
Despite the high death toll in malaria and the absence of vaccine candidates, public health experts made a tricky call to recommend the introduction of RTS, S beyond the trials – but they do so cautiously. Researchers will carefully follow the pilot vaccination programs in the three countries to determine efficacy and safety, and to determine how well parents manage to bring their children into all four vaccine doses. The findings will determine policy decisions on whether the vaccine should be used elsewhere in the future.
"We believe that this may be another tool – an imperfect tool with a modest effectiveness – as well as all other malaria control tools. which, however, can actually have a massive impact if used incompletely, "said Pedro Alonso, director of WHO's Global Malaria Program. Other antimalarial agents include insecticides that are sprayed indoors, bed nets, and improvements in the testing and treatment of malaria.
"We are dealing with a very, very hard organism," Dr. Alonso adds P. falciparum parasites that cause the disease. These are "really complex organisms," he said, and we do not know how long the researchers will need to develop a better vaccine.
The pilot programs aim to reach around 360,000 children each year in the three countries. It is designed to last five years, then public health experts will evaluate the future of RTS, p. 1965.