International Journal of Research and Innovation in Applied Science (IJRIAS) |Volume VIII, Issue I, January 2023|ISSN 2454-6194
Review On Malaria Vaccines: The Panacea for Africa
Chibuikem Nnamdi Akalazu1 and Omolade Olayinka Okwa2*
Department of Zoology and Environmental Biology, Faculty of Science, Lagos State University, Nigeria.
*Corresponding author
Abstract: – Plasmodium speciesare protozoa parasites responsible for clinical manifestations associated with malaria. The most prevalent are P. falciparum (Africa), P. vivax (Americas), P. ovale, P. malariae and P. knowlesi. Malaria control in Africa has been an endless battle. Global mortality for malaria in 2020 was 627,000 deaths with a significant portion of these occurrences in little children resident in Sub-Saharan Africa. Nevertheless, medical breakthroughs in vaccine technology have shown recorded success in highly endemic regions of Africa. The most promising being RTS,S- ASO1, R 21, PFSPZ with the R21 meeting the 75% efficacy threshold set by WHO and the RTS,S endorsed for widespread administration in high transmission areas. The success of these vaccines is largely due to their Pre-erthrocytic, erythrocytic and liver stage mode of action against the parasite. The circumsporozoite proteins (CSP) which are the most secreted antigens from the sporozoite stage of the Plasmodium parasite is the ideal biomolecule to serve as focus for heightened immune alertness in the circulatory and hepatic systems of Man. CSP in conjunction with several adjuvants and proteins serve to maintain a significant antibody titre over a period of months post vaccination hence drastically reducing the chances of malaria associated morbidities or mortality. This feat perhaps heralds a glimmer of hope on the possibilities of malaria eradication when integrated control options are employed in the fight against malaria.
Key words: Plasmodium falciparum, Malaria vaccines, RTS,S /ASO1, PFSPZ, R21, Africa.
I. Introduction
Malaria is established following the biological activities of invasive Plasmodium species in the circulatory and hepatic systems of vertebrates. Clinical manifestations associated with the disease are heightened by the aggressive efforts of the hosts’ immune system to find and neutralize the parasite, usually at the peril of delicateneighboring cells.There are over 150 different species of Plasmodium,with P. falciparum, P. malariae, P. vivax, and P. ovale reported as definitive hosts in humans. The parasite is transmitted by a tiny, adaptable, and mobile vector, the female Anopheles sp. (CDC, 2020; Okwa et al., 2012; Okwa, 2016).
WHO estimated 241 million cases of malaria occurred in 2020, with 228 million (95%) reported in Africa. Mortality associated with malaria in 2019 was reported at 558,000, an increase of 12% to an estimated 627,000 people, after years of steady declines.54% of malaria mortality was registered in only 4 countries: Nigeria (31.9%), Congo D.R (13.2%), Tanzania (4.1%) and Mozambique (3.8%) (WMR, 2021).The malaria prevalence in Nigeria for 2021 was such that 60% of outpatient’s visits to hospitals were due to the disease as well as 23% child mortality and 11% maternal mortality (The Guardian, 2022). By 2030, WHO set goals include the distribution of fully licensed vaccines with efficacy levels at least at 75% to reduce malaria morbidity worldwide, especially in endemic areas (MVFG, 2013).
The wide spread implementation of long lasting insecticide-treated nets, sanitary practices, as well as coatings on the inner walls of households with residual insecticides have all reduced the disease burden over time, but chemotherapy with artemisinin combination therapy (ACTs) is the most popular and perhaps effective approach for malaria control in endemic areas, as it keeps the parasite count in the blood at a relatively low level (WMR, 2021).There is no whole immunity against the parasites activity in the circulatory system and this is in part due to the complex forms of the parasite (Okwa et al., 2012). Hence recurrent bouts of the disease occur within a year in high transmission areas. The only viable option to Plasmodium control in humans is to keep the immune system primed to the presence of certain antibodies secreted by the parasite, a sort of “antibody policing”. This action is what is known as vaccination.