The feature of the influenza virus which is the reason behind synthesis of new vaccines for influenza every year is antigenic drift.
Antigenic drift is a phenomenon by which mutations give rise to genetic variations in pathogenic agents like viruses, which changes the viral surface proteins of the virus. These changes in the viral surface proteins in the antigen leads to the generation of new variations. These variations are new to the immune cells in the body and trigger them with different signals every time they infect a host. The best example to study this effect is the influenza virus which has numerous variations like influenza A, B, C and D. Thus, the influenza virus has to be produced or updated every year.
Learn more about the influenza virus here-
https://brainly.com/question/27429995
#SPJ4
