What is Antigenic Drift?

The competition between disease causing pathogens and our tactics to combat them are a never ending story. We have always been working on the edge to discover new ways to tackle the menace and threat imposed by pathogens and they in turn have been evolving newer strategies for survival. The flu has been with us for quite some time now. Although we have been doing our best to get rid of this common but potent human malady, we have not yet achieved complete success. This statement is illustrated by the present wave of swine flu sweeping over most parts of the world. There is so much to understand about the pathogenecity of the virus that causes this disease, and identifying specific details could help us gain a considerable advantage over it.

The human immune system identifies pathogens with the memory that it retains upon first contact. Once you’ve acquired antibodies against that specific pathogen a re-exposure is easily tackled by the immune system. However, any changes that would alter the identity of the pathogen to the immune system would render our immunity useless. In this regard, antigenic drift plays a significant role. It is also quite commonly confused with antigenic shift that is discussed here. Antigenic drift is a natural process that occurs in influenza, where the accumulation of natural mutations can slowly make a new strain with different antigenicity.

Image Credit: National Institute of Allergy and Infectious Diseases (NIAID)

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In the case of Influenza A, the process of Antigenic drift involves the slow accumulation of mutations in the genome that causes the pathogen to change its antigenic characteristics that make it difficult for the human immune system to tackle it. Since these pathogens carry RNA (ribonucleic acid) as their genetic material instead of DNA, the chances of natural mutations or changes in the genetic information propagates easily and is retained.

When an influenza vaccine is administered it provides the human body the capability of warding of attacks by the strains against which the vaccines were designed. However, owing to the phenomenon of antigenic drift the vaccine may be little or no help when faced with a strain that has altered epitopes (regions recognized by the immune system). Research is currently progressing towards better understanding how antigenic drift can be combatted with regard to health hazards and as to understand the phenomenon of pathogenicity itself.