Malaria is one of the leading causes of death caused by a parasite. According to the WHO, there were 229 million malaria cases worldwide and around 409,000 deaths in 2019. The African subcontinent has a high share in the global malaria burden and accounted for around 94% of the malaria cases and deaths in 2019. Children below the age of five are the most vulnerable to contracting the disease and accounted for around 67% of the total deaths caused by the parasite.
Plasmodium falciparum is the parasite responsible for this deadly infection and it resides in the gut of the female Anopheles mosquito. The mosquito transfers the parasite in the form of sporozoites by injecting its saliva into the bloodstream of the host. The sporozoites enter into the liver cells where the parasite completes one half of its life cycle to form merozoites. These merozoites go on to invade and multiply within the red blood cells causing the cells to burst, and hence beginning a new infective cycle.
Vaccine development for malaria has been slow. This is because the malarial parasite knows how to evade the immune system. The parasite travels from the skin to the bloodstream to the liver by which time it has developed several ways to remain invisible to the immune system. It multiplies in the liver and enters into the blood cells. The symptoms start to show only after a week of the entry of the parasite. By this point, it is too late to stop the pathogen and the infection.
The only malaria vaccine approved till date is RTS or Mosquirix developed by GlaxoSmithKline and has around 26-55% efficacy. The R21 vaccine developed by the University of Oxford is another candidate malaria vaccine which is in Phase II trials and it meets the 75% efficacy for a vaccine mandated by the WHO. On July 26th, 2021, BioNTech founder Ugur Sahin announced that the company plans to come up with a new type of mRNA malaria vaccine based on the success of the COVID-19 mRNA vaccine (Moderna vaccine developed along with Pfizer) and the trials for this vaccine are to go live by early 2022.
mRNA vaccines work a lot faster than many traditional vaccines. DNA or Deoxyribonucleic acid forms the framework of the genome and houses all the necessary genes responsible for the functioning of various enzymes and proteins. The information of the DNA gets converted into messenger RNA (mRNA) in the nucleus of the cell through a process called transcription. The mRNA then exits the nucleus into the cytoplasm where it forms a complex with the ribosomes and gets converted into proteins through a process called translation.
mRNA vaccines are basically parts of the mRNA that codes for the necessary proteins or the antigenic components of the pathogen. The mRNA from the vaccine will enter into the host cell and get translated into these antigens which will then prime the host immune system. Memory antibodies are made which will then help to clear out the pathogen more effectively the next time it enters the host system.
The most significant difference between an mRNA vaccine and live-attenuated or dead vaccines is that those more traditional ones carry disabled viruses with the respective surface proteins with them. mRNA vaccines, on the other hand, trigger the production of those proteins in the cells. mRNA vaccines are easier to develop than traditional vaccines and can be easily manipulated and adapted. Since the malarial parasite is a highly adaptable pathogen, researchers need to identify the types of antigenic proteins the malarial parasite can trigger in the human system so as to develop the appropriate types of mRNA for the vaccine. Researchers also need to identify ways that the parasite can be made available and visible to the immune system.
BioNTech plans on setting up mRNA manufacturing units all throughout Africa which could also be used to develop vaccines for other diseases. They want to establish an industrial or semi-industrial infrastructural unit which follows all the necessary rules and SOPs regarding vaccine production and quality control. BioNTech also wants to develop mRNA vaccines for various types of cancer and tuberculosis. The company has already started the phase 2 trials for an mRNA vaccine against skin cancer.
Some of the current antimalarial strategies include vector control and treatments include antimalarial drugs, most of which are expensive and have unfavourable side effects. The vector is also capable of developing drug resistance. Hence there is a necessity for developing vaccines as they are cheaper than most medications.