Influenza A virus A/Darwin/6/2021 (H3N2) recombinant hemagglutinin antigen

A seasonally-specific component of the influenza vaccine. The influenza vaccine, also known as the "flu shot", is a vaccine that helps to protect against infection from influenza viruses. These vaccines provide protection from influenza by exposing the immune system to the virus (or parts of the virus) which results in an immunological defense against future exposure to the virus, or "antigen". This defense includes the production of humoral immunity through the development of antibodies and of cell-mediated immunity through the production of T-lymphocytes. Upon re-exposure to an influenza virus, the immune system is prepared with circulating antibodies that identify and destroy the virus.

There are three basic types of vaccines available: inactivated influenza vaccine (IIV), live attenuated influenza vaccine (LAIV), and recombinant influenza vaccines (RIV). Inactivated vaccines contain a virus particle that has been grown in media and then subsequently killed, or inactivated, through exposure to heat or chemicals such as formaldehyde. Inactivated viruses cannot replicate and thus cannot cause disease from infection, even in immunocompromised individuals. In contrast, live vaccines are produced from "wild-type" or disease-causing viruses that have been attenuated, or weakened, through various laboratory techniques. Live vaccines maintain their replicative ability. Recombinant influenza vaccines are produced by synthesizing recombinant influenza hemagglutinin antigen in a laboratory and do not require the use of candidate viruses or egg-based manufacturing processes.