Malaria vaccine fails to protect people in Mali

By Vibha Varshney
Published: Thursday 31 May 2007

a malaria vaccine tried out in Mali in 2003 was not suited to protect people from the pathogen prevalent in the area, according to a joint study by researchers in Mali and the us. The researchers studied samples from people in Bandiagara, a rural town in northeastern Mali, and found that before administering the vaccine, its possible effect on the strain of mosquito being targeted was not taken into consideration.

Reporting the results of the study in the online journal Public Library of Science (plos) in November 2006, the researchers from University of Maryland School of Medicine, usa, University of Bamako, Mali, and National Institutes of Health, Bethesda, said the results showed the importance of determining the genetics of the pathogens before starting vaccine trials.

The main vector in the Mali countryside is Anopheles gambiae, which spreads the pathogen Plasmodium falciparum. A variety of strains of Plasmodium can cause malaria and different strains produce different antigens. These antigen are used to make vaccines. A vaccines is effective if it contains the same antigen as the parasite it has to produce antibodies against.

The research team collected 1,300 blood samples from malaria patients between July and January each year (1999-2001). They sequenced their dna to examine the presence of a particular gene--msp-119. The vaccine had been developed against one of the variants of this gene--3 d7. Data from 14 different variants of msp-119 were compared to find that 3d7 was present only in 16 per cent of the infections. Two other variants of the gene, fvo and fup, were present in about 40 per cent of the samples.

While 3d7-derived vaccine provides some protection against fvo and fup strains, it does not provide optimum immunity against them. Unfortunately, the 3d7-derived vaccine was tested in Mali where the other two variants were prevalent.

"We collected epidemiological data and samples between 1999-2001 and did the molecular analyses retrospectively in 2006," said Christopher V Plowe, lead author and head of malaria section of the Center for Vaccine Development at University of Maryland School of Medicine.

Such epidemiological studies would ensure that potentially effective vaccines are not abandoned because they were tested on incorrect populations. For example, a fvo or fup derived vaccine would probably be more effective in Mali than the 3d7 derived one but might not work in other places.
India scenario Preparations to test vaccines against falciparum malaria are underway even in India. The National Institute of Malaria Research (nimr), Delhi, has developed vaccine testing sites in Orissa and Madhya Pradesh. In Orissa, blood spots collected from people suffering from P. falciparum malaria showed that a total of 22 types of msp-1 antigens and 24 of msp-2 were prevalent in the area. Trials are yet to begin. nimr deputy director Sukla Biswas said epidemiological studies were being carried out. "Trials on suitable vaccines that will work in the area will be allowed," she says.

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