Ahh, malaria. The media tart of the parasite world. Various news outlets are reporting on an experimental malaria vaccine developed by PATH Malaria Vaccine Initiative and GSK, currently undergoing trials. Preliminary results have been published in the New England Journal of Medicine (which, incidentally, has an impact factor of about 4 gazillion). A quote from the journal article: “These initial results show that RTS,S/AS01 reduces malaria by half in children aged five-17 months during the 12 months after vaccination and that it has the potential to have an important impact on the burden of malaria in young African children.” A 50% reduction seems to be a good start, but will not achieve herd immunity, which is the point of vaccination. Perhaps over time, the researchers will improve the efficacy of the vaccine and further reduce the infection rate. But that’s not really the point I want to make about this. I do not doubt that malaria poses an unacceptable risk to health, particularly of children, in tropical areas. The stats on malaria-related morbidity and mortality are clear. In 2009, over 780,000 deaths were attributed to malaria, and most of those were children.
The skepticism I have for the success of this treatment is based on three things:
- that malaria often co-occurs with other parasitic diseases,
- the use of vaccines to control diseases involves many factors that potentially impede appropriate roll-out, including cost and logistics, and
- Plasmodium spp. are transmitted by vectors, which will mean that they will still be present in vaccinated populations.
The first thing: other parasitic diseases.
Even if children are able to be vaccinated and protected against malaria, they are still at very high risk of infection with one or more of many parasitic diseases that occur in tropical and subtropical areas. These diseases cause substantial morbidity, despite their mortality rates for any one disease being lower than that for malaria. The WHO has a list of neglected tropical diseases, all of which cause a high burden of disease in both adults and children. But, generally, the trend is that these diseases cause high morbidity, but not high mortality. Hookworm disease (caused by Ancylostoma duodenale and Necator americanus) causes anemia, malnutrition, growth wasting and stunting, and can cause cognitive deficits (Weaver et al. 2010 – indulge me while I cite myself). Around a billion people worldwide are infected with hookworm, or Ascaris, or Trichurus, or a combination of these helminths.
(lifecycle of hookworm from CDC website. Both species do it the same way)
Schistosomiasis, Chagas disease, Leishmaniasis etc all contribute an incredible burden of disease and affect peoples’ well-being and ability to be productive members of society. While kids may survive past their 5th birthday thanks to a malaria vaccine, they are still at high risk of physical and cognitive impairment due to neglected tropical diseases. There is a lot of research being done on effective treatment and control methods for combating these diseases. Indeed, there is a whole journal dedicated to research on these diseases, PLoS NTDs. But still, the importance of this gets overshadowed by the glamourpuss malaria.
The second thing: vaccine roll-out.
Vaccines cost money. And some of them are highly sensitive to things like temperature, or politics. Diseases that have been eliminated from many developed nations are still highly prevalent in developing nations, for different reasons. Polio is still endemic in India, Pakistan, Afghanistan and Nigeria, but infection rates are falling. This is a good thing. But it’s taken longer than anticipated to get this close to eradication. Political instability, war and religious tensions have all contributed to the current situation.
Poor countries that want to, but that cannot afford to, provide immunisations to their people put the cost and the onus on individuals. Many people in developing nations are poor, or live by subsistence, which means that they are unable to pay for appropriate healthcare. Therefore they miss out. Other things like food security and climate, in addition to numerous socioeconomic factors will influence how effectively a vaccine is rolled out.
The third thing: vector control.
A vaccine for malaria will not eliminate the pathogen. It is not like smallpox, where humans were the vectors and the success of the vaccine was due to reducing the prevalence of the virus in people so it could not be transmitted. Due to the life-cycle of Plasmodium, it will still happily circulate in mosquito populations, and pose the same health risks to unvaccinated people. Designing a vaccine without also developing appropriate vector-control practices seems like a band-aid solution.
It’s not my intention to deliberately rain on the parade of medical breakthroughs. But there are so many factors associated with malaria, and a vaccine will certainly not solve all of them. The term “multi-disciplinary approach” is thrown around a lot (I’ve used it myself), but I really think that it will be essential in combating malaria.
Ref: Weaver, Hawdon, Hoberg (2010) Soil-transmitted helminthiases: implications of climate change and human behavior. Trends Parastiol. 26, 574-581.