False about antigenic drift-

. <p>INFLUENZA:- Influenza viruses classified under the family ohomyxoviridae. 3 viral subtypes-A,B and C. These three are antigenically distinct.No cross immunity between them. Influenza A and B - responsible for epidemics throughout the world. Influenza A has 2 distinct surface antigens- hemagglutinin(H) and neuraminidase(N). The influenza A virus is unique among the viruses because it is frequently subjected to antigenic variation, both major and minor. ANTIGENIC SHIFT:- 1. Sudden complete or major change. 2. Results from genetic recombination of human with animal/an viruses providing a major antigenic change. 3. Can cause major epidemic/pandemic involving most/ all age groups. ANTIGENIC DRIFT:- 1. Antigenic change is gradual over a period of time. 2. Occurs due to point mutation in the gene owing to selection pressure by immunity in the host population. 3. Affected by previous antibodies. {Reference: park&;s textbook of preventive and social medicine, 23rd edition, pg no.154 }</p>