The Malaria Vaccine, a Dream or Reality?

In 2015 there were 214 million incidents of malaria spread across the globe, sounds like a lot doesn’t it? But this is actually progress! Between 2000-2015, there was a reduction of malaria occurrence by 37%, and a 60% reduction in the mortality rate. This is looking optimistic for the endemic regions of the worlds where malaria has taken its toll. Whilst the anti-malarial drugs remain the initial treatment for this parasitic disease, how close are we to finding a successful vaccine?

Generally, there are 3 approaches to the development of a malaria vaccine which each target varying stages of its lifecycle. There are pre-erythrocytic vaccines, this means the target is the sporozoites (premature parasites that infect liver cells), infected liver cell vaccine, meaning that the life cycle has been halted before entering the blood cells, and as malaria is carried by mosquitoes, a vaccine to interrupt mosquito-to-human transmission.

Image result for cdc plasmodium life cycle
The Life Cycle of Malaria: shows the different stages of the parasite life cycle, parts of this is what vaccines target

Although due to many of the endemic regions residing in Africa, the financial input towards developing a vaccine becomes a burden due to the countries with wealthier economies where malaria is not such a big issue, view it as a less useful investment for research as diseases like cancer are more prevalent in these countries.

Image result for malaria endemic areas WHO 2017
Endemic Regions 2012

So are there any suitable vaccines that look promising?
One of the most successful candidates to be used as a vaccine is the RTS,S vaccine, developed by WRAIR and GSK. This is the first vaccine to be licensed for human use against malaria and proves as a step forward to eliminating the disease.

It is thought that this is not the vaccine to eliminate the disease, but it does provide protection in children for up to 4 years.

This vaccine is only able to target one strain of malaria though, Plasmodium Falciparum. Despite falling efficacy over time, one of the main limitations to RTS,S is that it only recognises one protein, circumsporozoite protein, produced from sporozoites. However, it will help reduce parasite reproduction in the liver, and decrease the severity of disease.

Another successful candidate for a malaria vaccine is the GMZ2 vaccine. This has been developed from naturally acquired antibodies from those who have recovered from malaria. It is thought these antibodies will recognise the parasitic proteins and be able to combat the symptoms of disease.

It mainly targets two proteins which occur in the blood stage of the parasite life cycle. This vaccine was in phase 1 trials to assess the safety, efficacy and how well it produces an immune response to the disease in people who have never been exposed to the parasite.

Soon after in 2016, the vaccine reached phase 2 trials, of which it was concluded that the vaccine was well tolerated and produced an immune response, it also reduced the cases of malaria occurring in the endemic regions, but the efficacy of this vaccine needed to be improved in order for it to become more effective.

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This diagram shows the names of other vaccines participating in clinical trials and which stage of the life cycle they target

So it seems likely that in the near future we will have a vaccine for malaria, making it a reality. However there is a common problem between most vaccines that have been on trial and this is that their efficacy is not what it takes to completely immunise the public from the parasitic disease.

Perhaps a new approach is needed, maybe a similar way to the MMR vaccine mentioned in my previous blog, but instead of presenting three different diseases in one vaccine, there could be a mixture of all vaccines targeting different stages of the malaria life cycle, which may be able to deplete parasitic levels in patients significantly.

Lets be optimistic and hope the WHO target of a 90% decrease of cases being reached by 2030, and then like smallpox, we can eliminate malaria.

 

 

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