What is the significance of the antigenic drift and shift in the influenza A virus?

What is the significance of the antigenic drift and shift in the influenza A virus?


Antigenic drift and shift is the ability of the influenza A virus to mutate over time producing a different antigen. The immune system is unable to counter act the virus, since the new antigen is genetically different and is unable to bind to the immune receptors causing illness. Vaccines allows the immune system to recognise the new antigen as foreign and destroy the viron, but the virus’s are constantly changing due to errors in replication of the virus, as seen in the antigenic drift.


Antigenic drift occurs in all types of the influenza virus where initially a mutation occurs. During RNA replication ‘the viral genome makes an error every 10000 nucleotides’ which is the length of a virus RNA. Therefore most newly synthesised influenza viruses are mutants. The errors are caused by the absence of RNA proof reading enzymes so the antigens to the viruses’ surface change over time, whereas in antigenic shift, it is a rapid change in antigen where a sudden change occurs from one antigen to another. Antigenic shift only occurs with influenza A viruses since it effects mammals and birds. The virus is able to transfer from different species  and the immune system is unable to produce the antibodies to combat the foreign antigen causing the host to become ill. Also, two influenza A viruses can infect the same species simultaneously, to produce a new virus, having the same effect as previously stated. Vaccines can be used to minimise the affect of antigenic drift and shift, but the constant mutation of viruses can be difficult to control.




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