- To describe the immune response against the A/H1N1 strain using the HAI method 21 days after last vaccination with the 2010-2011 NH seasonal Trivalent Influenza Vaccine (TIV) administered 13 months after the first vaccination in a subset of subjects who received two half-doses of either t either formulation 1 or 2 of the A/H1N1 influenza vaccines as primary series.