Effectiveness of seasonal influenza vaccination in healthcare workers:
a systematic review
A.N.M. Nga,*, C.K.Y. Laib
aInfectious Disease Control Training Centre, Hospital Authority/Infection Control Branch, Centre for Health Protection, Department of Health, Hong Kong SAR, China
bSchool of Nursing, Hong Kong Polytechnic University, Hong Kong SAR, China
a r t i c l e i n f o
Received 22 August 2010
Accepted 6 August 2011
by J.A. Child
Available online 5 October 2011
s u m m a r y
Vaccination is considered a key measure to protect vulnerable groups against influenza
infection. The objectives of this review are to determine the effect of influenza vaccinations
in reducing laboratory-confirmed influenza infections, influenza-like illnesses (ILIs), working
days lost among vaccinated HCWs, and associated adverse effects after vaccination. Twenty-
two healthcare-related databases and internet resources, as well as reference lists, and the
bibliographies of all of the retrieved articles were examined. All randomized controlled trials
(RCTs) comparing the effectiveness of any kind of influenza vaccine among all groups of
HCWs with a placebo/vaccine other than the influenza vaccine/no intervention were
included in the review. Only three RCTs matched the inclusion criteria. There is a limited
amount of evidence suggesting that receiving influenza vaccination reduces laboratory-
confirmed influenza infections in HCWs. No evidence can be found of influenza vaccina-
tions significantly reducing the incidence of influenza, number of ILI episodes, days with ILI
symptoms, or amount of sick leave taken among vaccinated HCWs. There is insufficient data
to assess the adverse effects after vaccination. There is no definitive conclusion on the
effectiveness of influenza vaccinations in HCWs because of the limited number of related
trials. Further research is necessary to evaluate whether annual vaccination is a key measure
to protect HCWs against influenza infection and thus increase their confidence in the
vaccine. In the mean time, the direction of promoting influenza vaccination to HCWs can be
shifted from staff protection to patient protection, with accurate information to address
concerns and misconceptions.
? 2011 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.
Influenza is a highly contagious viral infection that leads to the
abrupt onset of respiratory symptoms. The attack rates of seasonal
influenza generally range from 10% to 20% in healthy adults, but
can exceed 80% in hospital outbreaks and long term care facili-
ties.1e5The transmission of influenza A (H1N1) causing the
pandemic in 2009 was even higher, as the majority of population
did not have such immunity to this strain, especially the younger
age group.6A review of the influenza pandemic in 2009 suggested
that 15e45% of the world’s population has already become
infected by this newly emergent strain.7Although influenza is
mostly a mild and self-limiting illness, it can pose a significant
demonstrated to be the most effective way to prevent influenza-
related complications among high risk populations such as chil-
dren, elderly and patients with comorbidity.10e12Healthcare
workers (HCWs) are also a target for the influenza vaccination
because they may serve as the vector for transmitting influenza
virus to patients after they become infected from either the
community or healthcare setting.2,13e16
Despite general consensus and recommendations for influ-
enza vaccination of HCWs, vaccine coverage among HCWs has
remained low and is far below the desired level to achieve herd
immunity.17e20The low vaccination rate among HCWs may be
associated with doubts over the effectiveness of the vaccine and
fear of its adverse effects.21Negative information regarding
* Corresponding author. Address: G/F, Centre for Health Protection, 147C, Argyle
Street, Kowloon, Hong Kong SAR, China. Tel.: þ852 2125 2922; fax: þ852 3523 0752.
E-mail address: email@example.com (A.N.M. Ng).
Available online at www.sciencedirect.com
Journal of Hospital Infection
journal homepage: www.elsevierhealth.com/journals/jhin
0195-6701/$ e see front matter ? 2011 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.
Journal of Hospital Infection 79 (2011) 279e286
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A.N.M. Ng, C.K.Y. Lai / Journal of Hospital Infection 79 (2011) 279e286