Lifestyle, socioeconomic characteristics, and medical history of elderly persons who receive seasonal influenza vaccination in a tax-supported healthcare system.
Observational studies on effectiveness of influenza vaccination in the elderly are thought to be biased by healthier lifestyles and higher socioeconomic status among vaccinated vs. unvaccinated persons. We examined this hypothesis in a uniform tax-supported health care system with free-of-charge influenza vaccination to the elderly.



We conducted a cross-sectional study among Danes aged 65-79years participating in a survey. We compared elderly persons with and without a recent (within six months) influenza vaccination in terms of (i) lifestyle and socioeconomic characteristics obtained from the survey and (ii) health factors including medical history provided by Danish registries. We compared the prevalence of study variables among vaccinated and unvaccinated persons using age- and sex-adjusted prevalence ratios (aPRs) with 95% confidence intervals (CIs).



Among the 4237 elderly persons completing the survey, 1718 (41%) had received an influenza vaccination. Vaccinated persons had more comorbidity than unvaccinated persons (aPR for high comorbidity level: 1.51 95% CI 1.24-1.84), were less likely to never have smoked (aPR: 0.88, 95% CI 0.80-0.97), and had a higher prevalence of physical inactivity (aPR: 1.08, 95% CI 1.03-1.13). Levels of education and income were similar in the two groups. Vaccinated persons had a higher prevalence of major physical limitations (aPR: 1.40, 95% CI 1.17-1.66) and need for assistance with activities of daily living (aPR: 1.29, 95% CI 1.13-1.47).



Elderly influenza vaccinated persons were not healthier in terms of lifestyle and burden of disease, did not have a higher socioeconomic status, and were more frail than unvaccinated persons.
Department of Clinical Epidemiology, Aarhus University Hospital, DK-8200 Aarhus N, Denmark; Clinical Pharmacology and Pharmacy, Department of Public Health, University of Southern Denmark, Denmark. Electronic address: mmhellfritzsch@health.sdu.dk.
Maja
M
Hellfritzsch
Department of Clinical Epidemiology, Aarhus University Hospital, DK-8200 Aarhus N, Denmark.
Reimar Wernich
RW
Thomsen
Department of Clinical Epidemiology, Aarhus University Hospital, DK-8200 Aarhus N, Denmark.
Lisbeth Munksgård
LM
Baggesen
Defactum, Central Denmark Region, DK-8200 Aarhus N, Denmark.
Finn Breinholt
FB
Larsen
Department of Clinical Epidemiology, Aarhus University Hospital, DK-8200 Aarhus N, Denmark.
Henrik Toft
HT
Sørensen
Department of Clinical Epidemiology, Aarhus University Hospital, DK-8200 Aarhus N, Denmark.
Christian Fynbo
CF
Christiansen
D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D003695:Delivery of Health Care; D003718:Denmark; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000517:prevention & control*; D008019:Life Style; D008297:Male; D012959:Socioeconomic Factors; D000073887:Vaccination Coverage
D007252:Influenza Vaccines
Aged; Confounding factors; Influenza vaccine; Observational studies as topic