Candidate malaria vaccine becomes less effective over time, study shows

Malaria, a disease which has always been a matter of concern, especially in the Asian and African continents, is responsible for millions of deaths and is a curse for human life. Eradication of malaria is a long cherished dream. Despite various control programmes backed by funding agencies, malaria caused 660,000 deaths in 2010, and the worst affected were infants and children under five [1].

The dismal fact that a child dies of malaria every minute just underscores the need for prevention of malaria. The very fact that vector control programmes have met with limited success in the past coupled with the need for expensive vigilance and monitoring warrants the need for targeting the parasite instead of focusing on mosquito control.

Extensive molecular level studies in the recent past provided new insights about the parasite and its survival strategies, but eradicating this menace has been a far cry so far, although several drug targeting studies are being performed all over the globe and new drug targets and potent inhibitors are being identified occasionally [2].

Most of the research in the past focused on the development of chemotherapeutic agents for treatment of malaria. As goes the popular adage that prevention is better than cure, an effective vaccine will prove more effective than temporary inhibitors in reducing the disease burden.

Several biological issues which led to failure of vaccine development are as follows:

Peculiarity of malaria parasite:
Complex life cycle of malaria and production of number of proteins by the parasite have been a serious concern from the beginning. The major setback for specific vaccine development was the wide antigenic diversity and lack of effective biomarkers of this parasite. Malaria genome is AT rich in nature and follows a different codon usage system leading to the antigenic diversity which is not usual in the closest organisms. Hence, targeting for a specific epitope for the parasite is similar to finding a needle in a haystack.

Other hurdles towards vaccine development:
The complex host-vector–parasite interaction always hinders the development of a proper animal model for vaccine testing. Similar issues are observed for developing important functional assays. Financial aspect of vaccine development is another important issue which cannot be ignored.
The concept of developing malaria vaccine following different life stages of the parasite got hampered many a times in the past.

Recent report of phase III clinical trial of RTS,S/AS01 vaccine, an excellent example of a joint effort of private and Government partnership raises the hope towards a better human life manifold. Even if efficacy of vaccine is reduced over a period, the prevention window is enough to save precious lives if we consider the numbers. Although, the obtained results are not promising complete protection against the disease and only targeting P. falciparum whereas as risk factor from other parasite species such as P. vivax is increasing, but it is definitely the first ray of light after a long darkness.

REFERENCE:
1. WHO Global Malaria Programme. World Malaria Report 2012.
2. Arora N, Banerjee AK. New targets, new hope: novel drug targets for curbing malaria. Mini Rev Med Chem. 2012 Mar; 12(3):210-26.