Effects of influenza vaccination of health-care workers on mortality of elderly people in long-term care: a randomised controlled trial

Background Vaccination of health-care workers has been claimed to prevent n osocomial influenza infection of elderly patients in long-term care. Data a re, however, limited on this strategy. We aimed to find out whether vaccina tion of healthcare workers lowers mortality and the frequency of virologica lly proven influenza in such patients. Methods In a parallel-group study, healthcare workers in 20 long-term elder ly-care hospitals (range 44-105 patients) were randomly offered or not offe red influenza vaccine (cluster randomisation, stratified for policy for vac cination of patients and hospital size). All deaths among patients were rec orded over 6 months In the winter of 1996-97. We selected a random sample o f 50% of patients for virological surveillance for influenza, with combined nasal and throat swabs taken every 2 weeks during the epidemic period, Swa bs were tested by tissue culture and PCR for influenza viruses A and B. Findings Influenza vaccine uptake in healthcare workers was 50.9% in hospit als in which they were routinely offered vaccine, compared with 4.9% in tho se in which they were not. The uncorrected rate of mortality in patients wa s 102 (13.6%) of 749 in vaccine hospitals compared with 154 (22.4%) of 688 in no-vaccine hospitals (odds ratio 0.58 [95% CI 0.40-0.84], p=0.014). The two groups did not differ for proportions of patients positive for influenz a infection (5.4% and 6.7%, respectively); at necropsy, PCR was positive in none of 17 patients from vaccine hospitals and six (20%) of 30 from no-vac cine hospitals (p=0.055). Interpretation Vaccination of healthcare workers was associated with a subs tantial decrease in mortality among patients. However, virological surveill ance showed no associated decrease in non-fatal influenza infection in pati ents.