DEVELOPING A MALARIA VACCINE
Malaria is a life-threatening disease caused by a parasite that is transmitted to people by the bite of an infected mosquito. It is particularly dangerous for young children and pregnant women.
Malaria can be prevented by avoiding mosquito bites. There have been many efforts to prevent cases of malaria by using mosquito nets or spraying chemicals that repel mosquitoes. However, not all cases of malaria can be prevented in this way – over 200 million people catch malaria each year, and over 90% of cases are in Africa.
That is one reason why a vaccine against malaria would be so useful. Another reason is that although malaria can be treated with medicines, there is a worrying increase in cases of malaria that are resistant to the medicines – and so cannot be treated. It is therefore very important to prevent as many cases of malaria as we can.
WHY IS IT SO DIFFICULT TO MAKE A MALARIA VACCINE?
The body system that defends against infections is called the immune system. Vaccines are designed to teach the immune system how to fight off a particular infection, without causing the person to become unwell in the first place. We already have many successful vaccines against viruses and bacteria that cause diseases. The vaccines are made from a weakened or killed form of the virus or bacteria – which the immune system can use to learn how to fight the disease.
It’s a simple idea, but has been very effective over lots of different infectious diseases.
However, malaria is not caused by a virus or a bacteria. Malaria is caused by a parasite, called plasmodium, and it is very difficult to make a vaccine that protects against plasmodium.
- The plasmodium parasite is much more complicated than a virus or a bacteria – in it’s structure, and in the way it causes damage to the body
- After people catch malaria, they do not automatically become immune to it. In fact, people can catch malaria many times over a lifetime. This is because, unlike the diseases for which we have effective vaccines (for example, measles), just being exposed to the malaria parasite does not give you lifelong protection against it.
This does not mean it will be impossible to develop a malaria vaccine. It is unlikely that there will be a vaccine soon that completely prevents malaria. However, a vaccine that just gave some protection against malaria, and reduced the chance of severe malaria and deaths from malaria, would still be very useful for people across Africa.
Over the past ten years there has been a lot of work to develop a vaccine against malaria. Two examples are discussed below.
THE PFSPZ VACCINE
The PfSPZ vaccine contains a weakened form of the whole plasmodium parasite that causes malaria. However it is not very useful, partly because in order to work, it must be stored at temperatures below 0 degrees at all times. Therefore, it is difficult to store and transport the vaccine, particularly in hot climates and areas where there is not always a consistent supply of electricity. In order for a malaria vaccine to be effective it needs to be able to reach as many people as possible – including people in remote rural areas.
THE RTS,S VACCINE
The RTS,S vaccine is different from the PfSPZ vaccine because it is a ‘subunit’ vaccine. It is made from a small part of the plasmodium parasite, not the whole organism – this is very important because it means that the vaccine does not have to be constantly stored at very low temperatures. There have been large clinical trials to test the RTS,S vaccine involving 15,000 children across sub-Saharan Africa, but the results of these trials were disappointing. For every ten people vaccinated, only 2 to 5 were protected against malaria, and the level of protection decreased after several months. For these reasons, the WHO has not yet recommended that it be used widely.
WHAT IS BEING DONE CURRENTLY?
Further clinical trials for RTS,S will take place between 2019 and 2022 in Ghana, Kenya and Malawi. They will be available through routine programmes to approximately 360,000 children aged between 5-24 months. Taking part in trials will speed up the vaccine development progress. Whilst this is ongoing, many laboratories worldwide are continuing to try to develop other malaria vaccines.