The vaccine is designed to enlist many parts of the human immune system to fight malaria parasites at various stages of their complex life cycle and hence would be very effective, says their report in the latest issue of the proceedings of the National Academy of Sciences of the United States.

The vaccine has been successfully tested in rabbits and the results ``provide a promising candidate for people living in malarious regions of the world,'' says Seyed Hasnain of NII, one of the team members. While the gene was synthesised at CDC, the vaccine in purified form was produced at Hasnain's gene expression laboratory in National Institute of Immunology.

Malariavaccines currently under development are based on special immune system triggering proteins, called antigens, produced by the parasite during one stage of its life cycle. However, vaccines based on a single antigen are limited because not all people respond to the same antigen, and parasites can create antigen variants to elude immune system surveillance. In contrast to malaria vaccines based on a single antigen, the new Indo-US vaccine incorporates multiple antigenic sequences from different development stages of the parasite and so is expected to provide a more-complete and long-range protection from the disease.

In assembling such a multistage, multi-component vaccine, the scientists used information gleaned from ongoing studies of natural immunity to malaria in western Kenya and experimental data to identify the most relevant portions of the nine malaria antigens.

They then combined the coding sequences for these key portions, called epitopes, into one synthetic gene as the basis for the new vaccinenamed CDC/NII Malvac-1, reflecting joint efforts of the Indian and American scientists.

Rabbits immunised with the vaccine produced antibodies that prevented malaria parasites from invading liver cells and replicating in the blood, according to the report.

``These findings demonstrate that the vaccine can induce response that block parasite development at multiple stages,'' the scientists said. Hasnain said trials currently going on in monkeys would have to be followed up by human trials by the end of the year.

The malaria parasite causes 300 million to 500 million new cases of illness and 1.5 million to 3 million deaths each year due in part to its increasing resistance to anti-malarial drugs, and the resistance of mosquitoes to commonly used insecticides.