Yearender 2021: the first vaccine against malaria, an important step in the gloom of Covid

In October, the World Health Organization (WHO) recommended the widespread use of the malaria vaccine RTS, S / AS01 (RTS, S) in children in sub-Saharan Africa and other areas where transmission of malaria to P. falciparum is moderate to high. Known by its brand name Mosquirix, the recombinant protein vaccine prevented 39% of malaria cases, 29% of severe malaria cases and also reduced the total number of hospitalizations.

According to the WHO World Malaria Report 2021, there were approximately 241 million cases of malaria in 2020 worldwide and six countries – Nigeria, Democratic Republic of the Congo, Uganda, Mozambique , Angola and Burkina Faso – accounted for about 55% of all cases.

The WHO South-East Asia Region accounted for about 2 percent of the burden and India accounted for 83 percent of the cases in the region. Despite this high burden, the WHO says India has seen a remarkable reduction in reported malaria cases and deaths.

The Global Malaria Report 2021 adds that globally, malaria deaths have declined steadily over the years – from 896,000 in 2000 to 558,000 in 2019. However, due to service disruptions during the pandemic of COVID-19, 2020 saw an increase in malaria deaths – 12 percent up from 2019.

Globally, 40 countries and territories have now achieved malaria-free certification from the 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 in 7-10 days and becomes merozoites. They are released from the liver cells and once in the bloodstream they invade the red blood cells and cause fever and other symptoms.

Life cycle of the malaria parasite. Life cycle of the malaria parasite. (PATH Malaria Vaccine Initiative)

Malaria vaccines are classified according to the stage of development of the parasite they target. The RTS, S vaccine targets the circumsporozoite protein on the surface of the sporozoite and prevents parasites from infecting liver cells.

To develop the new vaccine, two protein components of the parasite were expressed in genetically engineered Saccharomyces cerevisiae yeast cells formulated with adjuvant. An adjuvant helps create a stronger immune response.

Why has it been difficult to develop a vaccine against malaria?

The US CDC explains: “The development of a vaccine against malaria has encountered 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 the complex immune response to malaria infection is poorly understood. Malaria parasites are also genetically complex, producing thousands of potential antigens.

He adds that unlike many diseases for which we have vaccines, exposure to malaria parasites does not provide lifelong protection. Acquired immunity can only partially protect, and people can still be 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.

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