Shot of hope

A malaria vaccine shows encouraging results in trials

 
By Vibha Varshney
Published: Monday 15 November 2004

-- (Credit: EMKAY)scientists have developed a malaria vaccine that shows some success in controlling the disease. Though it will have to be used in combination with available drugs and preventive methods to offer full protection, experts hope it would prove especially useful in malaria-endemic regions. The vaccine is still in the trial phase.

Called rts,s/as02a or Mosquirix, the vaccine prepares the immune system to attack the sporozoite -- the form in which the malaria germ, Plasmodium falciparum, enters the bloodstream after a mosquito bite. It has been made possible through a partnership formed in the year 2000 between the multinational GlaxoSmithKline (gsk), which developed the vaccine in the mid 1990s, and Malaria Vaccine Initiative(mvi), a non-governmental organisation, which is funding the trials. In 1997, gsk had found the vaccine protected about 80 per cent of adult volunteers .

Phase i trials of Mosquirix were held in April 2001 in Gambia and Mozambique, and showed the vaccine was safe. Phase ii trials were carried out in two regions of Mozambique between April 2003 and May 2004. More than 2,000 children aged 1-4 years were recruited for the study and given either the vaccine or a placebo. Following the trials, vaccine efficacy against severe malaria attacks was found to be 58 per cent, according to a paper published in The Lancet (Vol. 364, No. 9443, October 16, 2004). The study was carried out by Pedro L Alonso of University of Barcelona, Spain and his team, which includes gsk scientists. An analysis of the results shows the vaccine might be more effective in younger children.

"These findings represent a breakthrough in the science of malaria vaccines," says Melinda Moree, director, mvi. "They provide convincing evidence that a vaccine could become part of the world's efforts to spare children and families from the devastating effects of this disease. This brings us another step closer to a licensed vaccine," she adds. The final test for the vaccine will be the phase iii trials.

Acute malaria affects almost 500 million people every year in the world. One to three million cases prove fatal; most deaths occur among children in Africa. The economic costs for Africa are equivalent to us $12 billion annually. That is why trials of the vaccine were held in Africa.
Elusive germ Scientists have been trying to make a malaria vaccine for the last 50 years. At least 25 different vaccines are under development. The major problem in making a successful vaccine is the complex nature of P falciparum. It has around 5,000 genes, which are in a constant state of change. Every time a drug or a vaccine comes close to controlling it, the pathogen just alters its genetic make up and escapes unscathed. Research, therefore, required a lot of money. But big pharmaceutical companies were not interested as the disease mostly affects developing countries where most people cannot to afford expensive medication. Work on this vaccine has been possible only because of the public-private partnership.

Phase iii trials will be crucial. In fact, the vaccine might not prove equally effective in all the genetic groups studied. Several human genes (such as those causing sickle cell anaemia and immune disorders) are known to influence susceptibility to malaria. These genes will potentially affect how a person responds to the vaccine. "The question now is can this formulation be improved by adding more potentially protective antigens," says David Arnot, who heads a malaria research group at the University of Edinburgh, uk.
Long way off Phase iii trials would also prove tedious as the number of participants would have to be more than that for phase ii trials. It is likely that the trials are carried out at a large number of locations, too. "We need to see how the vaccine will perform over a longer period of time, in younger children, and in different epidemiologic settings," says B Fenton Hall, chief, malaria vaccine development section, division of microbiology and infectious diseases, National Institutes of Health, usa . Even if the vaccine proves successful in phase iii trials, it is unlikely to reach the market before 2010.

Then, there is the question of cost. The product is estimated to be quite expensive: us $10-20 per dose. And, three doses will need to be given. At the current price, experts say that it would be unethical to market a vaccine, which has such a low efficacy. "The partnership would need to find ways of reducing the cost. One approach can be to manufacture it in a developing country as was the case with the hepatitis b vaccine produced by Shantha Biotechnics Limited, Hyderabad," says P V Venugopal, director, international operations, Medicines for Malaria Venture, Geneva.

Mosquirix may or may not turn out to be a perfect vaccine. However, it seems a step forward in the global fight against malaria.

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