Antigenic variation seen in which of the following-: (A) Influenza virus, (B) Hepatitis virus, (C) Yellow fever virus, (D) Leptospira
Answer is A. The influenza A virus is unique among the viruses because it is frequently subject to antigenic variation, both major and minor. When there is a sudden complete or major change, it is called a shift, and when the antigenic change is gradual over a period of time, it is called a drift. Ref:PARK&;S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 23rd edition,Page:154