Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Ribbon model of a monomer of the influenza hemagglutinin protein. Blue represents the HA1 portion, and the green is the HA2 portion. HA1 contains the receptor-binding domain and is the main target of the immune responses. HA2 is the anchor of the virus and is responsible for the fusion of the envelope and cellular endosomal membranes.
