- To describe the immune response against the A/H1N1 strain using HAI method 21 days after a vaccination with the 2010-2011 Northern Hemisphere (NH) seasonal trivalent influenza vaccine (TIV) administered 13 months after the first vaccination in a subset subjects who received the A/H1N1 influenza vaccine and in subjects naïve to the swine origin A/H1N1 strain.