H1N1: is the emergence of the 2009 A (H1N1) virus an example of antigenic shift or antigenic drift?explain the difference between shift and drift.
H1N1 1.Is the emergence of the 2009 A (H1N1) virus an example of antigenic shift or antigenic drift? Explain the difference between shift and drift. 2. Why was the 2009 A (H1N1) influenza epidemic considered a pandemic?