Effects of repeated annual influenza vaccination on antibody responses against unchanged vaccine antigens in elderly frail institutionalized volunteers.
Concern about the possibility that annually repeated influenza immunizationmayinduce a lower antibody response than first vaccination.
To ascertain the cumulative effects of yearly vaccination on serological response to unaltered vaccine antigens in the elderly.
The haemagglutination-inhibiting (HI) antibody response was examined in 158 elderly institutionalized frail volunteers subdivided in 3 groups according to the sequential winters in which each subject received a trivalent inactivated influenza vaccine. The study, conducted over 5 consecutive winters (from 1998/99 to 2002/03), reports the antibody response only for sequential years (2 or 3) in which the vaccine strain examined was not altered.
Significant increases in the values of HI antibody titres were observed after vaccination in each year examined against the different influenza vaccine strains used, except against B antigen in the second of the 3 winters studied (1999/00). The antibody responses found were not always adequate, i.e. at levels above the currently requested values for commercial vaccines (post-vaccination seroprotection rate >/=1:40, increases in geometric mean titres >/=2, positive responses >/=30% compared with pre-vaccination), probably because of old age (mean age >/=81 years) and the presence of underlying diseases in a high percentage of volunteers (>/=86%). The most frequent chronic diseases found werecardiovascular diseases (48%), endocrine disorders (19%), functional disability (10%) and pulmonary diseases (4%). The post-vaccination values observed in the sequential years were in general similar for A/H3N2 and A/H1N1 vaccine strains. A decrease, however, for some parameters at statistically significant levels, was observed against B antigen following repeated vaccine administrations.
Our data seem to support the possibility of a slight impairment of HI antibody response against unaltered influenza vaccine antigens, especially for influenza strains that have circulated for prolonged periods of time. Indeed a tendency to a lower response was found only against B/Beijing antigen, introduced in the vaccine composition in the winter 1995/96, but not against the A/H3N2 and A/H1N1 vaccine strains, which weremore frequently changed.
Department of Medical Surgery Specialities and Public Health, University of Perugia, Perugia, Italy. email@example.com
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Aged, 80 and over
Hemagglutination Inhibition Tests