All the following are true regarding Type A influenza virus, EXCEPT:
There are 16 subtypes of hemagglutinins. Rest of the statements given are true. Antigenic changes occurs only to a lesser degree in group B influenza virus. Influenza C virus appears to be antigenically stable. Note: Almost all of the pandemic which has ever occurred is due to Type A influenza virus. Ref: Park, Edition 21, Page - 143,144
There are only 14 subtypes of haemagglutinin
There are only 9 subtypes of neuraminidase antigen
Humans are generally infected by virus of subtype H1, H2 or H3 and N1 or N2.
It shows both antigenic shift and drift