The malaria vaccine RTS, S could enhance the production of antibodies protective in the case of a parasitic infection later, according to a study led by the Institute of Global Health of Barcelona (ISGlobal), an institution supported by “la Caixa”. The results, published in “BMC Medicine”, identify the antigen (or protein fragments) that could be included in future vaccines multivalent more effective.
In this study, the authors investigated how the vaccination affects the natural immunity to the parasite in a later exposure. “To date, most studies had focused on evaluating the specific responses to the vaccine, but not responses to other antigens of the parasite,” explains Gemma Moncunill, last author of the study. The RTS, S vaccine contains only one antigen of the parasite: a fragment of the protein CSP.
The immunity to a pathogen can be acquired by natural exposure to the organism or by vaccination. The mechanisms behind both types of immunity are not always the same, particularly in the case of parasites with complex life-cycles, such as Plasmodium falciparum, which causes malaria. In recent years, the researcher ISGlobal Carlota Dobaño and his team have been investigating the immune response induced by the RTS, S vaccine, the malaria vaccine, more advanced, and will be tested on a large scale in sub-saharan Africa this year.
The research team analyzed serum samples obtained from 195 children, vaccinated or not, who took part in the clinical trial of phase III RTS, S vaccine and were followed for 12 months. 78 were from Kintampo, Ghana, a region with high malaria transmission, and 115 were from Manhiça, Mozambique, where transmission is low to moderate. Studied the levels and type of antibodies directed against a total of 38 protein fragments (or antigens) of P. falciparum, including the protein CSP, before and after vaccination.
They found three patterns of antibody responses to these antigens: those that decrease after the vaccination, that do not change and that increase. Many antibodies in the first group are considered to be markers of exposure to parasites and were associated with an increased risk of malaria. The third group is related to protection: reduced by half the risk of contracting the disease. These protective antibodies recognize predominantly to antigens expressed by the parasite stages that circulate in the blood and infect red blood cells.
“We believe that the partial efficacy of the vaccine allows for low levels of infection on subsequent exposure to the parasite, which in turn leads to the production of protective antibodies, “explains Carlota Dobaño. “This effect is observed especially in regions with levels of transmission is low to moderate,” he adds.
Translated from ABC News https://www.abc.es/salud/enfermedades/abci-vacuna-podria-favorecer-adquisicion-inmunidad-natural-contra-malaria-201908140322_noticia.html