November 2008

A study from Utrecht, Netherlands (Plos Medicine, 2008;5(10):1453-1460) noted that while annual influenza vaccination of health care workers (HCWs) is advised in most Western countries, adherence to this recommendation is generally low. Although protective effects of this intervention for nursing home patients have been demonstrated in some clinical trials, the exact relationship between increased vaccine uptake among HCWs and protection of patients remains unknown owing to variations between study designs, settings, intensity of influenza seasons, and failure to control all effect modifiers. Using a mathematical model to estimate the effects of HCW vaccination in different scenarios and to identify a herd immunity threshold in a nursing home department, the researchers used a stochastic individual-based model with discrete time intervals to simulate influenza virus transmission in a 30-bed long-term care nursing home department. The model revealed a robust linear relationship between the number of HCWs vaccinated and the expected number of influenza virus infections among patients. In a realistic scenario, approximately 60% of influenza virus infections among patients can be prevented when the HCW vaccination rate increases from 0 to 100% vaccination. A threshold for herd immunity was not detected.

Content Updated (Tuesday, 6th January 2009)