The effectiveness of influenza vaccine against influenza a (H3N2) virus infections in nursing homes in Niigata, Japan, during the 1998-1999 and 1999-2000 seasons. Influenza vaccine and pneumonia mortality in a nursing home population. Effect of influenza vaccination of nursing home staff on mortality of residents: a cluster-randomized trial. Effects of a large-scale intervention with influenza and 23-valent pneumococcal vaccines in adults aged 65 years or older: a prospective study. Influenza vaccine effectiveness in preventing hospitalization for pneumonia in the elderly.
To evaluate the effectiveness of influenza vaccines against influenza-like illness (ILI) among nursing home residents.
                Prospective, nonrandomized, cohort study.
                Nine nursing homes during the 1998-1999 influenza season and 11 nursing homes during the 1999-2000 influenza season in Niigata Prefecture, Japan.
                Six hundred ninety-nine residents and 440 healthcare workers (HCWs) during the first season, and 930 residents and 517 HCWs during the second season, with vaccination rates ranging from 0% to 97.7%.
                Overall, ILI decreased from 24.3% during the 1998-1999 season to 8.8% during the 1999-2000 season. Multivariate analysis adjusted for several factors, including gender, age, underlying diseases, and resident and HCW vaccination rates, failed to demonstrate clear individual protection of residents (relative risk [RR], 1.42; P = .2 for the first season; RR, 0.95; P = .9 for the second season). However, vaccination rates of 60% or greater for residents and HCWs reduced the risk of ILI, and also could prevent outbreaks during the 2 seasons. Highly impaired activities of daily living and chronic respiratory diseases were significantly associated with increased ILI.
                A high vaccination rate for both residents and HCWs may reduce the risk of ILI and institutional outbreaks in nursing homes. The effectiveness of immunization against influenza in elderly persons is uncertain. A retrospective cohort study in a New York City nursing home examined the occurrence of pneumonia and its related mortality over three consecutive influenza seasons (Nov 1 through April 30, 1979 to 1980, 1980 to 1981, and 1981 to 1982). Nearly one half of approximately 450 residents (mean age, 84 years) accepted immunization each year. The vaccinated and unvaccinated groups were similar. The attack rate of pneumonia did not differ significantly between the vaccinated and unvaccinated groups in any of the three influenza seasons. When influenza was occurring in the community (1979 to 1980 and 1980 to 1981), however, the risk of death from pneumonia in the unvaccinated group was three-fold higher than in the vaccinated group (60% vs 18% and 73% vs 25%, respectively). In a year when influenza was specifically sought and not found in the facility (1981 to 1982), however, vaccination did not affect pneumonia-related mortality. This study also suggests that estimates of mortality due to pneumonia should include deaths that occur up to 60 days after onset of pneumonia; shorter follow-up may overestimate the protective effect of vaccination. To evaluate the effect of staff influenza vaccination on all-cause mortality in nursing home residents.
                Pair-matched cluster-randomized trial.
                Forty nursing homes matched for size, staff vaccination coverage during the previous season, and resident disability index.
                All persons aged 60 and older residing in the nursing homes.
                Influenza vaccine was administered to volunteer staff after a face-to-face interview. No intervention took place in control nursing homes.
                The primary endpoint was total mortality rate in residents from 2 weeks before to 2 weeks after the influenza epidemic in the community. Secondary endpoints were rates of hospitalization and influenza-like illness (ILI) in residents and sick leave from work in staff.
                Staff influenza vaccination rates were 69.9% in the vaccination arm versus 31.8% in the control arm. Primary unadjusted analysis did not show significantly lower mortality in residents in the vaccination arm (odds ratio=0.86, P=.08), although multivariate-adjusted analysis showed 20% lower mortality (P=.02), and a strong correlation was observed between staff vaccination coverage and all-cause mortality in residents (correlation coefficient=-0.42, P=.007). In the vaccination arm, significantly lower resident hospitalization rates were not observed, but ILI in residents was 31% lower (P=.007), and sick leave from work in staff was 42% lower (P=.03).
                These results support influenza vaccination of staff caring for institutionalized elderly people. The effectiveness of influenza and pneumococcal vaccination in the prevention of hospital admissions and death has not been assessed prospectively. We have therefore examined the effects of influenza and pneumococcal vaccination in individuals aged 65 years and older in a 3-year prospective study, between Dec 1, 1998 and May 31, 1999.
                All individuals in Stockholm County aged 65 years or older (259,627) were invited to take part in a vaccination campaign against influenza and pneumococcal infection. We recorded for all vaccine recipients (100,242) name, and date of birth, and whether they had been given both or one of the vaccines. All individuals (> or = 65 years) admitted to hospital in Stockholm County with influenza and pneumonia related diagnoses were identified between Dec 1, 1998, and May 31, 1999.
                The incidence (per 100,000 inhabitants per year) of hospital treatment was lower in the vaccinated than in the unvaccinated cohort for all diagnoses: 263 versus 484 (-46% [95% CI 34-56]) for influenza; 2199 versus 3097 (-29% [24-34)) for pneumonia; 64 versus 100 (-36% [3-58]) for pneumococcal pneumonia; and 20 versus 40 (-52% [1-77]) for invasive pneumococcal disease. The total mortality was 57% (55-60) lower in vaccinated than in unvaccinated individuals (15.1 vs 34.7 deaths per 1000 inhabitants).
                These findings show that general vaccination leads to substantial health benefits and to a reduction of mortality from all causes in this age group. During the winter of 1989-1990, influenza type A(H3N2) circulated widely, causing excess morbidity and mortality nationwide. From November through April, 1989-1990, hospitalized cases of pneumonia and influenza occurring among noninstitutionalized individuals 65 or more years of age were identified by 20 acute care hospitals in southern lower Michigan. These cases were group matched on age, sex, race, and zip code to randomly sampled, community-based controls from a comprehensive listing of Medicare beneficiaries residing in the study area. Self-reported data were collected from cases and controls on influenza vaccine status for the 1989-1990 season and on a number of other factors which could have influenced vaccination status or outcome. Questionnaires were completed by 1,907 individuals, 449 of whom were cases, resulting in an overall response rate of 76%. A community-based influenza surveillance system was implemented to determine the timing and intensity of viral activity and influenza-like illness. Vaccine effectiveness in preventing overall pneumonia and influenza hospitalizations was estimated by logistic regression. During the 3-month period of surveillance-confirmed peak influenza type A(H3N2) circulation, vaccine effectiveness was 45% (95% confidence interval 14-64, p = 0.009). However, during the 3-month period of low or absent virus activity, identical methodology and model specification resulted in an effectiveness estimate of 21% that was not statistically different from zero (p = 0.36). The effectiveness determined during the peak period of virus circulation is felt to be a conservative estimate, since agents other than influenza are responsible for pneumonia and influenza hospitalizations, even during times of peak influenza activity.
No effect was shown for specific outcomes: laboratory-proven influenza, pneumonia and death from pneumonia. An effect was shown for the non-specific outcomes of ILI, GP consultations for ILI and all-cause mortality in individuals ≥ 60. These non-specific outcomes are difficult to interpret because ILI includes many pathogens, and winter influenza contributes < 10% to all-cause mortality in individuals ≥ 60. The key interest is preventing laboratory-proven influenza in individuals ≥ 60, pneumonia and deaths from pneumonia, and we cannot draw such conclusions.
The identified studies are at high risk of bias.
Some HCWs remain unvaccinated because they do not perceive risk, doubt vaccine efficacy and are concerned about side effects. This review did not find information on co-interventions with HCW vaccination: hand washing, face masks, early detection of laboratory-proven influenza, quarantine, avoiding admissions, anti-virals, and asking HCWs with ILI not to work. We conclude there is no evidence that vaccinating HCWs prevents influenza in elderly residents in LTCFs. High quality RCTs are required to avoid risks of bias in methodology and conduct, and to test these interventions in combination.