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Diminishing Returns with Healthcare Worker Influenza Vaccination?

Amesh A. Adalja, MD, FACP, FACEP, FIDSA, November 6, 2015

In recent years there has been an increasing call for optimizing rates of healthcare worker vaccination against influenza. In response, some organizations have called for mandatory influenza vaccination policies to be instituted at hospitals. Consequently, many hospitals have instituted mandatory policies, citing patient safety and the threat of nosocomial influenza transmission.

However, new data, presented at this year’s Interscience Conference of Antimicrobial Agents and Chemotherapy (ICAAC), raise some questions about this approach and provide some context for assessment of the risk of nosocomial influenza.


No Association of Vaccine Rates with Nosocomial Influenza

Dionne and colleagues from the University of New Mexico conducted a retrospective cross-sectional study aimed at evaluating the rate of nosocomial influenza acquisition and healthcare worker vaccination rates over 5 influenza seasons spanning 2010 to 2015. During this period, influenza vaccination rates among healthcare workers at their institution increased from 47% to 96%.

Nosocomial influenza rates, however, did not significantly decrease over the same period. Additionally, logistic regression analysis did not reveal any association between healthcare worker influenza vaccine rates and rates of nosocomial influenza. 


Ceiling Effect

Dionne et al’s conclusions are that perhaps a ceiling effect of healthcare worker vaccination against influenza is reached at around 50% and that further increases in vaccination do not significantly affect nosocomial influenza rates. 

An implication of this important work—which merits replication—is that once a threshold of 50% healthcare worker influenza vaccination is reached, other interventions may become important. More restrictive visitor policies, enhanced compliance with infection control, and more testing for influenza among inpatients may be required to further decrease nosocomial influenza rates. 

As the study addressed only nosocomial influenza rates, the important benefit of healthcare worker influenza vaccination on minimizing absenteeism through self-protection against influenza remains a compelling reason to advocate for a 100% vaccination rate.  



Dionne B, Brett M, Culbreath K, Mercier RC. Limited effect of healthcare worker influenza vaccination rates on the incidence of nosocomial influenza infections. Presented at the Interscience Conference of Antimicrobial Agents and Chemotherapy (ICAAC) 2015: Abstract I-296;  September 18, 2015; San Diego, CA. Accessed November 4, 2015.