Wed. Aug 21st, 2019

A vaccine could favor natural immunity against malaria



A vaccine against malaria, RTS, S, could favor the acquisition of natural immunity against the parasite that causes this tropical disease, which in 2017 caused about 435,000 deaths worldwide according to estimates by the World Health Organization (WHO ).

According to a study led by the Institute of Global Health of Barcelona (ISGlobal), a research center promoted by "la Caixa", this malaria vaccine could favor the production of a series of protective antibodies after parasite infection.

The results of the study, published in "BMC Medicine", identify which antigens (protein fragments) could be included in the design of future multivalent vaccines, which are more effective.

ISGlobal recalled in a statement that immunity against a pathogen can be acquired naturally, that is, after natural exposure to it, or thanks to a vaccine.

Sometimes, this research center underlines, the mechanisms behind these two types of immunity are not the same, particularly in the case of parasites with complex life cycles, such as "Plasmodium falciparum", the parasite that causes malaria.

The team of Carlota Dobaño, a researcher at ISGlobal, has been studying the immune response induced by RTS, S, the most advanced malaria vaccine to be implemented this year on a large scale in sub-Saharan Africa.

The study has analyzed how RTS, S, the most advanced vaccine against malaria, affects the natural immunity subsequently acquired against the parasite that causes the disease, the "Plasmodium falciparum", which is transmitted by a mosquito bite.

The antigens that have been identified in this research are capable of creating protective antibodies that reduce half the risk of contracting malaria, a disease that is the leading cause of infant mortality in Africa.

"So far, the vast majority of RTS, S studies have focused on evaluating specific vaccine responses, not evaluating their influence on responses to other parasite antigens," said Gemma Moncunill, the last author of the study.

The research team has analyzed serum samples obtained from a total of 195 girls and boys in Ghana and Mozambique, vaccinated or controlled, who participated in phase 3 of the clinical trial of RTS, S and those who followed for 12 months.

The levels and type of antibodies directed against a total of 38 protein fragments (or antigens) of the parasite were studied, before and after vaccination, including the CSP protein that is the only antigen of the parasite that contains the RTS, S vaccine.

Researchers have found three profiles of antibody responses against these 38 antigens: those that decrease after vaccination, those that do not change, and those that increase.

The antibodies in the third group, which increase, have reduced the risk of contracting malaria by half.

These protective antibodies mostly recognize antigens expressed by the phases of the parasite that circulate in the blood and infect the red blood cells.

"We believe that the partial efficacy of RTS, S allows, when there is subsequent exposure to the parasite, the level of infection is low enough to favor the production of these protective antibodies. This effect would be appreciated especially in regions with moderate levels of These results indicate that the antigens in question could be included in future, more effective, multivalent vaccines. " underlined the researcher Carlota Dobaño.

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