Comparative study on immunogenicity among split, intradermal and MF59-adjuvanted influenza vaccines in elderly institutionalized subjects

Introduction The reduced immunogenicity and effectiveness of influenza vaccines in subjects presenting higher risk of influenza-related complications, hospitalizations and deaths, led the innovative drive to search for new strategies to implement the immune response elicited by influenza vaccines including addition of adjuvants, and use of alternative routes of antigen delivery. We carried out a spontaneous blinded study in order to compare the immunogenicity of an inactivated split vaccine (Vaxigrip®, Sanofi Pasteur MSD), of an MF59-adjuvanted subunit vaccine (Fluad®, Novartis Vaccines and Diagnostics) and of an intradermal (Intanza® 15mcg, Sanofi Pasteur MSD) influenza vaccines. Methods The vaccines used contained the three strains recommended by the WHO for the 2012–2013 influenza season (A/Victoria/361/2011 (H3N2), A/California/7/2009 (H1N1) and B/ B/Wisconsin/1/2010). Twenty-six volunteers (mean age 78 years) were immunized with Vaxigrip®, 137 (mean age 86 years) with Fluad® and 89 (mean age 84 years) with Intanza®. Titers of hemagglutination inhibiting antibodies to different vaccine antigens were determined for serum samples taken before and 1 month after vaccination by a standard microtiter method. The results were evaluated according to the Committee for Medicinal Products for Human Use (CHMP) criteria for approval of influenza vaccines in the elderly. Results The two potentiated vaccines induced a good antibody response at least against A/H3N2 and B antigens, while the split vaccine tended to fulfill the CHMP criteria less often. The antibody responses induced by potentiated vaccines were similar although those against the B antigen tended to be higher in subjects vaccinated with intradermal vaccine than in individuals receiving MF59-adjuvanted vaccine. None of the vaccine used was able to induce a satisfactory response against the A/H1N1 component vaccine. Conclusion Intradermal vaccination and use of MF59 adjuvant appear to be appropriate strategies to address the challenge of declining immune response in the elderly after influenza vaccination.