A Critical Review on Human Malaria and Schistosomiasis Vaccines: Current State, Recent Advancements, and Developments

Abstract

Malaria and schistosomiasis are two major parasitic diseases that remain leading causes of morbidity and mortality worldwide. Co-infections of these two parasites are common in the tropics, where both diseases are endemic. The clinical consequences of schistosomiasis and malaria are determined by a variety of host, parasitic, and environmental variables. Chronic schistosomiasis causes malnutrition and cognitive impairments in children, while malaria can cause fatal acute infections. There are effective drugs available to treat malaria and schistosomiasis. However, the occurrence of allelic polymorphisms and the rapid selection of parasites with genetic mutations can confer reduced susceptibility and lead to the emergence of drug resistance. Moreover, the successful elimination and complete management of these parasites are difficult due to the lack of effective vaccines against Plasmodium and Schistosoma infections. Therefore, it is important to highlight all current vaccine candidates undergoing clinical trials, such as pre-erythrocytic and erythrocytic stage malaria, as well as a next-generation RTS,S-like vaccine, the R21/Matrix-M vaccine, that conferred 77% protection against clinical malaria in a Phase 2b trial. Moreover, this review also discusses the progress and development of schistosomiasis vaccines. Furthermore, significant information is provided through this review on the effectiveness and progress of schistosomiasis vaccines currently under clinical trials, such as Sh28GST, Sm-14, and Sm-p80. Overall, this review provides insights into recent progress in malarial and schistosomiasis vaccines and their developmental approaches.

Keywords: R21/Matrix-M; RTS,S/AS01; Sm-p80; antigen; clinical trial; malaria; schistosomiasis; vaccine.

Figure 1

Human malaria vaccines: current state and developments at different stages. Pfs230 (Plasmodium falciparum Pfs230 protein); Pfs25 (Plasmodium falciparum Pfs25 protein); Pfs47 (Plasmodium falciparum Pfs47 protein); R21/MM (R21/Matrix-M™ vaccine); RTS’S/AS01 (repeated T-epitopes derived from PfCSP and S-antigen derived from hepatitis B surface antigen and the AS01 adjuvant); PfSPZ (Plasmodium falciparum sporozoite); CVac (chemically modified vaccine); GAP (genetically attenuated parasite); RBC (red blood cell); MSP (merozoite surface protein); AMA-1 (apical membrane antigen 1); PfRH-5 (Plasmodium falciparum reticulocyte-binding protein homolog 5); EBA-175 (erythrocyte-binding antigen 175).