Malaria is a mosquito-borne infectious disease affecting humans and other animals caused by parasitic protozoans belonging to the Plasmodium type. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. Symptoms usually begin ten to fifteen days after being bitten.
Malaria vaccine is a vaccine that is used to prevent malaria. The only approved vaccine as of 2015 is RTS,S. It requires four injections, and has a relatively low efficacy (26–50%). Due to low efficacy, WHO does not recommend the use of RTS,S vaccine in babies between 6 and 12 weeks of age.
The vaccine is going to be studied further in Africa in 2018. Research continues into recombinant protein and attenuated whole organism vaccines.
RTS,S (developed by PATH Malaria Vaccine Initiative (MVI) and GlaxoSmithKline (GSK) with support from the Bill and Melinda Gates Foundation) is the most recently developed recombinant vaccine. It consists of the P. falciparum circumsporozoite protein (CSP) from the pre-erythrocytic stage. The CSP antigen causes the production of antibodies capable of preventing the invasion of hepatocytes and additionally elicits a cellular response enabling the destruction of infected hepatocytes. The CSP vaccine presented problems in trials due to its poor immunogenicity. RTS,S attempted to avoid these by fusing the protein with a surface antigen from hepatitis B, hence creating a more potent and immunogenic vaccine. When tested in trials an emulsion of oil in water and the added adjuvants of monophosphoryl A and QS21 (SBAS2), the vaccine gave protective immunity to 7 out of 8 volunteers when challenged with P. falciparum.
RTS,S/AS01 (commercial name Mosquirix), was engineered using genes from the outer protein of P. falciparum malaria parasite and a portion of a hepatitis B virus plus a chemical adjuvant to boost the immune response. Infection is prevented by inducing high antibody titers that block the parasite from infecting the liver. The developers are non-profit In November 2012 a Phase III trial of RTS,S found that it provided modest protection against both clinical and severe malaria in young infants.
As of October 2013 preliminary results of a phase III clinical trial indicated that RTS,S/AS01 reduced the number of cases among young children by almost 50 percent and among infants by around 25 percent. The study ended in 2014. The effects of a booster dose were positive, even though overall efficacy seem to wane with time. After four years reductions were 36 percent for children who received three shots and a booster dose. Missing the booster dose reduced the efficacy against severe malaria to a negligible effect. The vaccine was shown to be less effective for infants. Three doses of vaccine plus a booster reduced the risk of clinical episodes by 26 percent over three years, but offered no significant protection against severe malaria.
In a bid to accommodate a larger group and guarantee a sustained availability for the general public, GSK applied for a marketing license with the European Medicines Agency (EMA) in July 2014. GSK treated the project as a non-profit initiative, with most funding coming from the Gates Foundation, a major contributor to malaria eradication.
On 24 July 2015, Mosquirix received a positive opinion from the EMA on the proposal of the vaccine to be used to vaccinate children aged 6 weeks to 17 months outside the European Union.
By 2020, the MVIP (Malaria Vaccine Pilot Programme) is expected to provide initial insights on the programmatic feasibility of delivering the RTS,S/AS01 vaccine candidate (trade name Mosquirix™) in real-life settings and on the safety profile of RTS,S in the context of routine use. The MVIP will continue monitoring feasibility and safety through its expected conclusion in 2022, while also generating results on the vaccine’s impact on childhood survival. The results of the MVIP will help inform future decisions on the wider-scale deployment of the vaccine.
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