The slow accumulation of genetic changes to an influenza virus over time is referred to as

Antigenic drift refers to the slow accumulation of genetic changes to an influenza virus over time.

Explanation:

Antigenic drift is defined as the mechanism by which viruses undergo variation. This mechanism involves the slow accumulation of mutations in the viral genes, that are responsible for coding the antibody binding sites. This leads to the formation of a new strain of virus, which can't be inhibited by the old antibodies. Due to this, the virus can easily spread the disease.

The antigenic drift occurs in the influenza A virus and also the influenza B viruses.

Therefore, Antigenic drift refers to the slow accumulation of genetic changes to an influenza virus over time.          

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