title: Antibody responses to intradermal or intramuscular MF59-adjuvanted influenza vaccines as evaluated in elderly institutionalized volunteers during a season of partial mismatching between vaccine and circulating A(H3N2) strains.
abstract: BACKGROUND
  The age-related weakening of the immune system makes elderly subjects less responsive to influenza vaccination. In the last years, two "enhanced vaccines" were licensed for individuals aged ≥65 years, one being a subunit vaccine (Fluad®) containing the MF59 adjuvant administered intramuscularly (IM-MF59) and the other one a split non-adjuvanted vaccine administered intradermally (Intanza® 15mcg) (ID). In the present study, we evaluated and compared the antibody responses against the three vaccine antigens and heterovariant A(H3N2) circulating viruses induced by IM-MF59 and ID influenza vaccines in 80 elderly institutionalized volunteers (40 per group) during the Winter season 2011-2012.
  
  
  RESULTS
  Hemagglutination inhibiting (HI) antibody titers were assessed in blood samples collected before, 1 and 6 months after vaccination. One month after vaccination both the IM-MF59 and ID vaccines induced increases in HI titers against all the three vaccine strains. The results in the two groups were similar against the A(H3N2) and A(H1N1) strains. Responses against the B strain typically tended to be higher after ID than IM-MF59, yet both vaccines stimulated lower responses against the B strain than against the two A strains. The two vaccines induced favorable results also against four epidemic drifted A(H3N2) viruses circulating in Winter 2011-2012. Six months after vaccination, the HI titers decreased in both groups.
  
  
  CONCLUSIONS
  The responses induced by IM-MF59 and ID vaccines in institutionalized elderly people were similar against the A(H3N2) and A(H1N1) strains but frequently higher, for the ID, against the B strain. The two vaccines induced positive responses against drifted A(H3N2) circulating viruses.
authors.affiliation: Department Experimental Medicine, University of Perugia, Piazza Gambuli, Perugia 06132, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Camilloni
authors.affiliation: Department Experimental Medicine, University of Perugia, Piazza Gambuli, Perugia 06132, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Basileo
authors.affiliation: Department MIPI Istituto Superiore di Sanità, Viale Regina Elena 299, Rome 00161, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Di Martino
authors.affiliation: Department MIPI Istituto Superiore di Sanità, Viale Regina Elena 299, Rome 00161, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Donatelli
authors.affiliation: Department Experimental Medicine, University of Perugia, Piazza Gambuli, Perugia 06132, Italy.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Iorio
keywords: Homologous and heterologous antibodies; Intradermal influenza vaccine; MF59-adjuvanted influenza vaccine