title: Partial Protection Induced by 2011-2012 Influenza Vaccine Against Serologically Evidenced A(H3N2) Influenza Virus Infections in Elderly Institutionalized People.
abstract: Ninety-two institutionalized elderly subjects were vaccinated with trivalent influenza inactivated vaccine available for the 2011-2012 season, characterized by a prevalent circulation of A(H3N2) influenza viruses (A/Victoria/208-clade) presenting antigenic and genetic patterns different from the A(H3N2) vaccine component (A/Perth/16/2009-clade). Haemagglutination inhibiting (HI) antibody titers were determined in sera collected before, 1 and 6 months after vaccination and patients were considered positive for serological evidence of recent infection if they had a seroconversion on comparing HI titers found in sera collected 1 and 6 months after vaccination. No seroconversions were found against A(H1N1) and B vaccine components. Instead 17 volunteers seroconverted against all or at least some of the different A(H3N2) antigens examined, i.e. the 2011-2012 (A/Perth/16/2009) and the 2012-2013 (A/Victoria/361/2011) vaccine strains and four drifted viruses belonging to the A/Victoria/208-clade circulating in the area were the elderly people were living. The results obtained suggest that influenza infections in the vaccinated volunteers might be due both to a poor match between vaccine and circulating A(H3N2) viruses, since 1 month after vaccination 15 of the 17 volunteers had post-vaccination HI titers considered protective (≥40) against the A(H3N2) vaccine antigen, but not always against the epidemic strains, and to a waning of vaccine induced immune response, since 6 months after vaccination HI titers of non-infected volunteers were found to be decreased as compared with those found 1 month after vaccination.
authors.affiliation: Department of Experimental Medicine, University of Perugia, Piazza Gambuli, 06132, Perugia, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Camilloni
authors.affiliation: Department of Experimental Medicine, University of Perugia, Piazza Gambuli, 06132, Perugia, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Basileo
authors.affiliation: RP Bittoni, Città della Pieve, Perugia, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Menculini
authors.affiliation: Azienda USL2, Foligno, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Tozzi
authors.affiliation: Department of Experimental Medicine, University of Perugia, Piazza Gambuli, 06132, Perugia, Italy. annaiorio42@gmail.com.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Iorio
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000914:Antibodies, Viral / Q000276:immunology*; D005260:Female; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control*; D008297:Male; D012189:Retrospective Studies; D013997:Time Factors; D014611:Vaccination
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines
keywords: Antigenic drift; Influenza virus; Protection; Vaccination