Oct 20 2011

Malaria Vaccine

Malaria is a serious illness in humans caused by several species of mosquito-born parasite (Plasmodium falciparum, vivax, and ovale). The CDC reports:

 In 2008, an estimated 190 – 311 million cases of malaria occurred worldwide and 708,000 – 1,003,000 people died, most of them young children in sub-Saharan Africa.

Efforts to reduce the incidence of malaria have largely focused on reducing the number of mosquitoes and preventing bites (for example by providing netting to cover beds), and these efforts can be very successful. But despite these measures malaria remains the 5th largest cause of death worldwide from infectious disease.

It was therefore exciting news when GlaxoSmithKline (GSK) announced a successful clinical trial of a new anti-malaria vaccine. The vaccine is the result of 24 years of research led by Joe Cohen. The report:

Final stage clinical trial data on RTS,S, also known as Mosquirix, showed it halved the risk of African children getting malaria, making it likely to become the world’s first successful vaccine against the deadly disease.

The vaccine is targeted at the liver stage of the parasite, keeping it from multiplying and giving the body a chance to wipe it out before it returns to the blood. In a clinical trial of 16,000 children, the largest clinical trial ever conducted in Africa, the vaccine proved to be safe and about 50% effective. That leaves a lot of room for improvement. Clearly this one vaccine by itself will not be enough to eradicate malaria, but it can significantly reduce the burden of this disease. Further research will hopefully improve its efficacy over time.

GSK estimates that if all goes well they should be able to have the vaccine on the market by 2015. Let’s hope all goes well. It will be interesting to watch the effect of this vaccine on the incidence and disease burden of malaria for the decade following the start of its use. The 50% reduction might have a magnified effect due to reducing the spread of the parasite by interrupting its life cycle. This degree of protection is not enough to provide “herd immunity” but it will still help reduce the prevalence of the parasite.

Other methods of fighting malaria will still be necessary, such as reducing mosquito populations and providing protective netting. I hope the use of the vaccine does not provide a false sense of security that reduces the use of other measures. This could have a paradoxically negative effect. There are many examples of this – such as people using sunscreen getting excessive sun exposure, or people who think they are driving a safe car driving more recklessly. So use of the vaccine will need to be combined with education measures to be sure the population understands this is just one of many measures that still need to be taken.

I also wonder how effect the vaccine will have to become in order for eradication to be likely. The typical figure given is 90-95%, but that applies to organisms that spread directly from person to person. I don’t know if it applies to a parasite with the complex life cycle of Plasmodium.  Also, Plasmodium has non-human reservoirs, meaning some species also infect vertebrates other than humans. So even if a highly effective vaccine were available the parasite could continue to exist in these other animals. So a human vaccine alone cannot achieve eradication.

But eradication can still be achieved if the population of Plasmodium is significant reduced by reducing human hosts, and then other measures, for example aimed at the mosquito part of the life cycle, may achieve eradication. It should be noted that the CDC achieved eradication of malaria in the US without the use of a vaccine.

In any case, the vaccine is a powerful additional tool in the fight against malaria. It will likely save millions of lives and significantly help the effort to reduce or eradicate malaria worldwide.

8 responses so far

8 thoughts on “Malaria Vaccine”

  1. ccbowers says:

    “…or people who think they are driving a safe car driving more recklessly.”

    This example doesn’t ‘ring true.’ I would have thought that a group people who buy safer cars are a group that would drive safer regardless of the car they purchased (self selecting risk averse people). The examples of this effect that I often think of are in regards to foods… e.g. eating more of the low fat ice cream (or more of any food that is perceived to be healthier).

    The progress with the malaria vaccine is great as an addition to current efforts (assuming it all pans out). I am curious to see how the $ will work out considering the wealth and (in)stability of many of the countries with the most malaria.

  2. Bronze Dog says:

    I tend to prefer safety in my cars, and I drive defensively regardless of my car choice, so that doesn’t ‘ring true’ on my anecdotal level. But I suppose I wouldn’t be surprised if there’s a segment of the population who would act that way.

    An example that might work better for an automotive analogy: Apparently a sizable portion of drivers stopped wearing seatbelts when car companies started adding airbags, resulting in more deaths and injuries from side collisions, which might have been preventable if they wore their seatbelts.

  3. SARA says:

    I read recently that the incidence of Malaria is down in the last 10 years, due to the more effective and timely intervention by targeting the worst areas.

    They predicted an even greater reduction by 2015. (perhaps due to the upcoming vaccine)

  4. bachfiend says:

    Sonia Shah has written a very readable book ‘The Fever. How Malaria Has Ruled Humankind for 500,000 Years’.

    10 years isn’t long enough to know whether the incidence of malaria is decreasing. It’s highly dependent on climatic conditions, ambient temperature and rainfall (with formation of puddles for the mosquitoes to breed). The incidence goes up and down each year. If you start your 10 years with a peak, then of course it’s going to look as though the incidence is decreasing (similar to the way AGW skeptics claim that global warming has stopped by starting their series in 1998, a warm year due to a strong el Nino).

    A vaccine is an advance, albeit a small one.

    Regarding safety in cars. For years, American car manufacturers have been advertising large SUVs as being safe. And American car buyers have been forced to buy cars much larger than necessary because they feel threatened by the large numbers of larger SUVs on the road. So ‘safe’ cars lead to unsafe roads.

  5. jre says:

    There is cause to hope that a 50% reduction in malaria infections might be sufficient to break the back of an epidemic in some locations, because the malaria lifecycle is more complicated than that of a disease transmitted directly between individuals. In places where malaria is endemic, its incidence fluctuates as the parasite is transmitted between vector and human host. Studies in what was then known as Ceylon found that the period between malarial peaks was regular and corresponded to Plasmodium’s incubation time in the mosquito’s gut — that’s how the malarial lifecycle was discovered. If the vaccine reduces disease prevalence below some threshold during the “troughs”, that may be enough to bring the whole shebang to a halt. The best book I’ve found on the subject is Mosquitoes, Malaria, and Man: A History of the Hostilities Since 1880 by Gordon A. Harrison.

  6. grottomatic says:

    I know this vaccine has been a long time coming, and although it isn’t advertised its real use is for people with zero exposure to malaria deploying to an endemic area and for children, who are often the ones who die from falciparum (I am wondering the cost of deploying this vaccine to endemic areas). Chloroquine and other prophylaxis are now ineffective in many parts of africa and south america (south of the panama canal), so hopefully this vaccine works well in practice – although I am very curious about its effectiveness against vivax and ovale (relapsing malaria) which can be a lifelong disease (although not as severe as falciparum).

    No matter its use or effectiveness, the real culprits in the spread of falciparum are humans and the focus of malaria control needs to remain anopheles mosquito control – by the (intelligent) use of DDT. No one wants to hear this of course, but if you don’t want malaria in tropical climates you need to spray aggressively and use agents against larvae in standing water. People forget that p. vivax and p. malariae used to be endemic to the american south, and the agressive use of DDT eradicated anopheles (as well as almost eradicating the bald eagle). Everything in medicine has a side effect, and this vaccine will be no different.

  7. TrickBrown says:

    I would say a potential 50% reduction in malaria is cause for celebration. Fear of malaria and wicked huge wild animals prevents me from even wanting to visit Africa. (I know the latter may be a little paranoid, but they’re wicked huge!)

    Anyway, in regards to ccbowers concern for the money involved, I know Bill Gates has spent a lot of money in his philanthropic efforts against malaria, perhaps this is something he can invest in and get a good return on that investment.

  8. Kawarthajon says:

    This sounds a lot like the HIV vaccine being developed in Thailand, where it is partially effective, but not enough to justify reducing other efforts to control the disease.

    As for the comments about the cars – many people who buy SUV’s, as an example, buy them because they are deemed to be safer cars. They are actually less safe because, as Steve pointed out, people do not drive them in a way they should be driven. Their most prevalent hazard is their weight – they take much more force to stop than a smaller sedan-style car. In winter driving conditions, they are known to slip more easily, slide further and they tend to roll much more easily than sedan-style cars, making them much more hazardous. Because they often have all-wheel drive and look like they’d be good off-roading, people tend to drive them faster and ignore the fact that they are actually more dangerous.

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