In October, the World Health Organisation (WHO) recommended the widespread use of the RTS,S/AS01 (RTS,S) malaria vaccine among children in sub-Saharan Africa and in other regions with moderate to high P. falciparum malaria transmission. Known by its brand name Mosquirix, the recombinant protein vaccine was found to prevent 39 per cent cases of malaria, 29 per cent cases of severe malaria and also reduced the overall hospital admissions.
According to WHO’s World malaria report 2021, globally, there were about 241 million malaria cases in 2020 and six countries – Nigeria, Democratic Republic of Congo, Uganda, Mozambique, Angola and Burkina Faso – accounted for about 55 per cent of all cases.
The WHO South-East Asia Region accounted for about 2 per cent of the burden and India accounted for 83 per cent of cases in the region. Despite this high burden, WHO says that India has shown a remarkable reduction in reported malaria cases and deaths.
The World malaria report 2021 adds that globally, malaria deaths have reduced steadily over the years – from 896000 in 2000 to 558000 in 2019. However, due to service disruptions during the COVID-19 pandemic, 2020 saw an increase in malaria deaths – 12 per cent rise compared with 2019.
Globally, 40 countries and territories have now been granted a malaria-free certification from WHO – including, most recently, China, El Salvador, Argentina and Uzbekistan.
Infection and vaccination
When an infected female Anopheles mosquito bites a person, it injects Plasmodium parasites into our bloodstream. The parasite – in the form of sporozoites – quickly enters the liver and multiplies over 7 to 10 days and becomes merozoites. They are released from the liver cells and once in the bloodstream invade red blood cells and cause fever and other symptoms.
Life cycle of the malaria parasite. (PATH malaria vaccine initiative)
Malaria vaccines are classified based on which parasite developmental stage they target. The RTS,S vaccine targets the circumsporozoite protein on the sporozoite surface and prevents the parasites from infecting the liver cells.
To develop the new vaccine, two protein components of the parasite were expressed in genetically engineered Saccharomyces cerevisiae yeast cells and formulated using an adjuvant. An adjuvant helps create a stronger immune response.
Why was it difficult to develop a malaria vaccine?
The US CDC explains: “The development of a malaria vaccine has faced several obstacles: the lack of a traditional market, few developers, and the technical complexity of developing any vaccine against a parasite. Malaria parasites have a complex life cycle, and there is a poor understanding of the complex immune response to malaria infection. Malaria parasites are also genetically complex, producing thousands of potential antigens.”
It adds that unlike the many diseases for which we have vaccines, the exposure to malaria parasites does not confer lifelong protection. The acquired immunity can only protect partially and people can still become infected with the parasite. Sometimes, the infection can also persist for months without any symptoms.
A recent editorial in The Lancet notes that the success of this new RTS,S vaccine is the culmination of generations of scientific ingenuity, three decades of research and development, and close collaboration within African communities.
