Answer:
Mutation in influenza virus occurs frequently.
Explanation:
It is possible for the influenza virus to increase in different tissues during each subsequent year, and immune memory is limited only to those tissues that have been initially infected.
The initial nfection with influenza weakens the immune system.
Mutation in the influenza virus occurs frequently.
Answer:
A primary reason for needing a new vaccine for influenza each year is that mutation in the influenza virus is frequent.
Explanation:
Influenza Viruses mutation is known as Antigenic shift.
This is the random accumulation of mutations in the haemagglutinin (HA), and to a lesser extent neuraminidase (NA) genes, recognized by the immune system. It is most pronounced in influenza A viruses.
As is the case in all RNA viruses, mutations in influenza viruses occur frequently because the virus' replication machinery does not have a proofreading mechanism. When such changes cause mutations in the antigenic sites of the HA or NA genes, which reduce or inhibit the binding of neutralizing antibodies (the basis for resolving infection in an individual), the virus may evade the immune system.
This process is the occurrence of seasonal influenza epidemics that may differ in severity and age groups affected. It also accounts for vaccine mismatch when one of the strains selected for the vaccine does not optimally match the circulating strains. As a result, annual changes in the composition of influenza vaccines are necessary.
Antigenic drift in the NA can lead to resistance against neuraminidase inhibitors. Antigenic drift may also allow a virus to cross the species barrier to a new host.
