A synthetic vaccine consisting of hemagglutinin (HA) antigens derived from three inactivated influenza viruses, two different influenza type A strains and one influenza type B strain. Trivalent influenza vaccine (TIV) is formulated annually, based on influenza strains projected to be prevalent in the upcoming flu season. Upon administration, the TIV provides active immunization against the three influenza virus strains, thereby protecting against influenza infection. A form of TIV containing higher concentrations of HA antigens may be used in older patients to elicit a more effective immune response.