Malaria Vaccination: For Better or For Worse?



(Source: www.mosquito.org)

Malaria is one of the most dangerous diseases on the planet, killing around 1300 children each day in Sub-Saharan Africa. The news, therefore, that a potential vaccine could be out in the next couple of years is good, right? Perhaps not.

Science is rarely that simple, sadly, and to understand why, we need to take a quick look at the malaria parasite itself. Firstly, there are not one, but four species of malaria parasite that infect humans. The vaccine in question: RTS,S, only targets on: Plasmodium falciparum.

Secondly, the parasite changes throughout its lifetime, going from mosquitoes to human blood, into human liver cells, back to blood and then back into mosquitoes. This may not sound like a big issue, but it’s the equivalent of a fugitive putting on various masks and outfits; it becomes harder for a vaccine to find and track. The current vaccine offerings get over this by only targeting one location at a time. Many of the ones in early testing target the blood stage, but RTS,S affects the liver cell stage, where the parasite does most of its growing.

Thirdly, and possibly most importantly, the malaria parasite reproduces sexually. While, again, this may sound like a non-issue, this essentially means that it can develop and pass on resistance genes to the vaccine much easier if it is not quickly dealt with. It’s the same reasoning as cross-pollinating plants in order to make them more resistant to disease as it increases the diversity of the organism.

This last point is made clear by Andrew Read, who published a paper in 2004 showing that parasites that passed through people who had already been vaccinated were more dangerous than otherwise; they had adapted some mechanism to ‘dodge’ the immune response, and the way that they had done this had made them more deadly.

Add to that the fact that the vaccine is at most 36% effective (on children aged 5 to 17 months) and you end up with an interesting issue: Is it worth it? Is it worth waiting until a more effective vaccine is found, or is it best to make do with what we have now, knowing what we know about its limited effectiveness?

If the disease was less dangerous, it might be worth waiting; the drugs used to treat malaria are good enough with the right care to keep you alive almost 100% of the time. However, with an estimated 584,000 deaths from malaria in 2013, even the low end of the RTS,S effectiveness, 18% in babies that had not received a booster jab, means that that is over 100,000 people potentially saved.

The trick is to use the vaccine effectively: prioritise areas of high malaria transmission, couple it with malaria drug therapies, such as artemisinin-combinations, make sure that insect nets are given out, and getting prompt diagnosis where cases of malaria do occur.

At the end of the day, malaria is a disease on the run. As we develop better treatments and vaccines for the parasite and work out ways to stop the mosquito transmitting them, malaria will go the way of smallpox- confined to the history books. Western Europe eradicated it by the 1930s, the US managed it by 1951. Africa is the last major bastion of the disease. Anything that the parasite does to try and make itself more dangerous only delays the inevitable, and therefore anything we can do to eliminate it is worth it.

#JamieHakham #Health #Malaria

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