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Impact on Mortality and Influenza-Associated Morbidity

Bettie C. G. Voordouw, MD, MPH; Paul D. van der Linden, PharmD, PhD; Simon Simonian, PhD; Johan van der Lei, MD, PhD; Miriam C. J. M. Sturkenboom, PharmD, PhD; Bruno H. C. Stricker, MD, PhD

Arch Intern Med. 2003;163:1089-1094.

Background  Influenza-related morbidity and mortality have been extensively studied with hospital and reimbursement data. However, little is known about the effectiveness of the annual vaccination programs in generally healthy community-dwelling elderly. The objective of our study was to investigate the effectiveness of influenza vaccination in community-dwelling elderly during the 1996 to 1997 influenza epidemic.

Methods  We performed a population-based cohort study using the computerized Integrated Primary Care Information database in the Netherlands. Subjects who were 65 years and older in 1996 with a permanent status in a practice in the source population were considered eligible for study participation. Two cohorts were defined on the basis of vaccination status. We estimated and compared all-cause mortality, pneumonia, and clinical influenza infection rates between the cohorts.

Results  Influenza vaccination was associated with a significant reduction of morbidity and mortality in vaccinated elderly (relative risk [RR], 0.72; 95% confidence interval [CI], 0.60-0.87). Influenza infections decreased significantly in the vaccinated population (RR, 0.48; 95% CI, 0.26-0.91). Mortality was reduced significantly in elderly with comorbidity (RR, 0.67; 95% CI, 0.48-0.94). The risk reduction for pneumonia was nonsignificant (RR, 0.77; 95% CI, 0.55-1.07) but was temporally related to the peak influenza activity.

Conclusions  In this study, influenza vaccination was associated with decreased mortality and influenza infections in community-dwelling elderly. Our results indicate that, in a season of mild influenza activity and good antigenic match between vaccine strains and circulating strains, influenza vaccination reduced mortality in the vaccinated population. Our data support an annual vaccination strategy for all community-dwelling elderly.

From the Pharmaco-epidemiology Unit, Departments of Internal Medicine and Epidemiology & Biostatistics (Drs Voordouw, van der Linden, Sturkenboom, and Stricker) and Department of Medical Informatics (Drs van der Lei and Sturkenboom), Erasmus Medical Centre, Rotterdam, the Netherlands; Medicines Evaluation Board, the Hague, the Netherlands (Drs Voordouw and Simonian); and Department of Drugs and Medical Devices, Inspectorate for Health Care, the Hague (Dr Stricker). The authors have no relevant financial interest in this article.

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