Hepatitis B Immune Globulin provides immediate passive immunity by supplying high titers of anti-HBs antibodies. These antibodies bind to circulating hepatitis B virus particles and hepatitis B surface antigen (HBsAg), neutralizing the virus and preventing its attachment and entry into hepatocytes. This action reduces viral replication and establishment of infection. Passive immunity offered by HBIG is temporary, typically lasting 3 to 6 months, which is why it is used alongside active vaccination for long-term protection.