Two Outbreaks of Influenza A (H3N2) in a Japanese Nursing Home in the
Winter of 1996-1997, with Differing Vaccine Efficacy
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NAOYA MURAYAMA,1,2
HIROSHI SUZUKI,1
MASAAKI ARAKAWA,2
KUNIAKI NEROME,3
KATSUMI MIZUTA4 and
KOHEI KAMEYAMA5
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1Department of Public Health and 2Department of
Internal Medicine, Niigata University School of Medicine, Niigata
951-8510, 3Department of Virology, National Institute of
Infectious Diseases, Tokyo 162-8640, 4Clinical Research
Division, Sendai National Hospital, Sendai 982-0045, and
5Sun-Plaza Nagaoka, Nagaoka 940-2111
Sixty of 128 (46.9%) residents of a nursing home were immunized with two
doses of the trivalent split influenza vaccine. They developed
7.4-11.5-fold antibody increases, with a 69-82% protection rate,
presenting good immune response rates to the influenza vaccine. Two
outbreaks of influenza A (H3N2) occurred. There were no significant
antigenic differences among the vaccine strain and the strains isolated
from both outbreaks in haemagglutination-inhibition tests, suggesting
that the second might have been a reoccurrence. There were no residents
who were infected in both outbreaks. The vaccine efficacy against
clinical illness in the first outbreak of typical influenza-like-illness
(ILI) was 51% (relative risk: 0.49), and the febrile period was reduced
significantly by vaccination. In the second outbreak, however, in which
all patients had atypical ILI with a high fever but not respiratory
symptoms, vaccine efficacy was not apparent for unknown reason.
Key words---
influenza; vaccine efficacy; aging; immunization
© 1999 Tohoku University Medical Press
Tohoku J. Exp. Med., 1999, 188, 289-298
Address for reprints: Naoya Murayama, M.D., Department of Public Health,
Niigata University School of Medicine, Niigata 951-8510, Japan.
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