Abstract
BackgroundAnnual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries, but 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. Therefore, we use 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.Methods and FindingsWe use a stochastic individual-based model with discrete time intervals to simulate influenza virus transmission in a 30-bed long-term care nursing home department. We simulate different levels of HCW vaccine uptake and study the effect on influenza virus attack rates among patients for different institutional and seasonal scenarios. Our model reveals 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 1. A threshold for herd immunity is not detected. Due to stochastic variations, the differences in patient attack rates between departments are high and large outbreaks can occur for every level of HCW vaccine uptake.ConclusionsThe absence of herd immunity in nursing homes implies that vaccination of every additional HCW protects an additional fraction of patients. Because of large stochastic variations, results of small-sized clinical trials on the effects of HCW vaccination should be interpreted with great care. Moreover, the large variations in attack rates should be taken into account when designing future studies.
Highlights
Annual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries to reduce transmission of influenza to vulnerable patients [1]
Annual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries, but adherence to this recommendation is generally low. 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
The absence of herd immunity in nursing homes implies that vaccination of every additional HCW protects an additional fraction of patients
Summary
Annual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries to reduce transmission of influenza to vulnerable patients [1]. A few clinical trials have demonstrated protective effects of this intervention for patients in nursing homes at relatively low HCW vaccine uptake rates [2,3,4,5]. Adherence to the recommendation is generally low [6,7,8,9] and it is uncertain what the effect of a further increase of vaccine uptake among HCWs is and whether herd immunity can be attained in health care institutions [10]. Annual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries, but adherence to this recommendation is generally low. To provide maximum protection against influenza, each year’s vaccine contains disabled versions of the major circulating strains of influenza viruses
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