Intradermal and intramuscular 2011-2012 influenza vaccination of elderly institutionalized volunteers: induction of antibody responses against vaccine and epidemic influenza virus strains

BACKGROUND. The new strategies proposed for implementing the immune response elicited by influenza vaccines in the elderly, include using adjuvanted vaccine or intradermal vaccination route. The aim of the present study was to explore and compare the ability of INTANZA® (Sanofi-Pasteur), an intradermal (ID) split-virion influenza vaccine, and of FLUAD® (Novartis), an intramuscular (IM) MF59-adjuvanted subunit influenza vaccine, to induce antibody response against vaccine antigens and against circulating A(H3N2) strains in elderly institutionalized people. MATERIALS AND METHODS. Study population and vaccination: Eighty elderly (≥65 years) people living in two nursing homes in Umbria, Italy, were vaccinated with one dose of 2011-2012 trivalent influenza vaccine (A/Perth/16/09, H3N2; A/California/7/09, H1N1; B/Brisbane/60/08) in November 2011. Forty of the 80 volunteers were randomly assigned to receive the IM (N= 40) or the ID (N=40) influenza vaccine. The antigenic content of the two vaccines was the same (15 µg). Vaccine immunogenicity: vaccine immunogenicity was evaluated measuring haemagglutination inhibiting (HI) antibody titers in sera collected prior and one month after vaccination and at the end of the influenza season, i.e. 6 months after vaccination. HI titer were determined, using guinea pig red blood cells (0.75%), against the three vaccine strains and against four A(H3N2) field isolates circulating in the 2011-2012 winter in Italy (A/Perugia/6/12, A/Perugia/20/12, A/Perugia/44/12 and A/Perugia/50/12). RESULTS. Comparing HI titers found before and 30 days after ID and IM vaccination significant increases were observed not only against the A(H1N1) and A(H3N2) vaccine antigens, but also against the epidemic A(H3N2) strains, found to be closely genetically correlated with A/Victoria/361/11, the new A(H3N2) vaccine component for the forthcoming 2012-2013 season. Responses against the vaccine B strain were higher in the group vaccinated with ID as compared with IM vaccine and the differences between the percentage of positive response were statistically significant. The criteria of the European Commission were always satisfied against the three vaccine strains, except for one parameter against B antigen in people receiving FLUAD®, whereas the requested values of seroconversions were in most instances not reached against the epidemic strains both after ID or IM vaccination. Six months after vaccination, antibody titers decreased against all the vaccine and epidemic strains studied. The titers found in people vaccinated with ID vaccine tended to be higher as compared with those observed after IM vaccine. CONCLUSION. This study, although limited in the size, demonstrated the ability of both INTANZA® and FLUAD® influenza vaccines for the 2011-2012 season to induce significant antibody responses against the three vaccine antigens and epidemic A/H3N2 viruses. However, the responses against the B antigen and the persistence of antibodies six months after vaccination tended to be higher in subjects vaccinated with ID vaccine than in individuals receiving IM vaccine.