Influenza vaccination for healthcare workers who care for people aged 60 or older living in long-term care institutions

Review question
We wanted to know if vaccinating healthcare workers against influenza reduces the risk of older individuals in long-term care institutions (LTCIs) acquiring influenza infections from healthcare workers.

Background
The signs and symptoms of influenza are similar to those of many other respiratory illnesses, therefore it is important in studies testing the effects of influenza vaccination to prove by laboratory tests, which are highly accurate, whether residents in LTCIs actually have influenza or another respiratory illness.

Study characteristics
Our evidence is current to October 2015. Overall five studies were included in our review but we used data from three trials with 5896 residents . In one trial the average age was 77 and 71% were female, in another this was 82 years and 70% were female, and in the last this was 86 years and 77% were female. One study was supported by the Greater Glasgow Health Board Care of the Elderly Unit, one by the Wellcome Trust and for one there was no statement.

Key results and quality of the evidence
The method of randomisation used was at low risk in two trials and unclear in one. In all three studies allocation concealment and blinding were unclear. In two studies data could not be included from everyone who was recruited and this put their results at a high risk of bias. All three studies reported outcomes completely. However, in all three trials there was performance bias due to incomplete influenza vaccination of healthcare workers in the intervention arms. No studies reported on adverse events.

Offering influenza vaccination to healthcare workers who care for those aged 60 or over in LTCIs may have little or no effect on laboratory-proven influenza (low quality evidence). HCW vaccination programmes probably have a small effect on lower respiratory tract infection (moderate quality evidence), but they may have little or no effect on admission to hospital (low quality evidence). It is unclear what effect vaccination programmes have on death due to lower respiratory tract illness (very low quality evidence) or all cause deaths (very low quality evidence).

This review did not find information on other interventions used in conjunction with vaccination of healthcare workers (for example, hand-washing, face masks, early detection of laboratory-proven influenza, quarantine, avoiding new admissions, prompt antiviral use, asking healthcare workers with an influenza-like illness not to work). High quality randomised controlled trials testing combinations of these interventions are needed.

Authors' conclusions: 

Our review findings have not identified conclusive evidence of benefit of HCW vaccination programmes on specific outcomes of laboratory-proven influenza, its complications (lower respiratory tract infection, hospitalisation or death due to lower respiratory tract illness), or all cause mortality in people over the age of 60 who live in care institutions. This review did not find information on co-interventions with healthcare worker vaccination: hand-washing, face masks, early detection of laboratory-proven influenza, quarantine, avoiding admissions, antivirals and asking healthcare workers with influenza or influenza-like illness (ILI) not to work. This review does not provide reasonable evidence to support the vaccination of healthcare workers to prevent influenza in those aged 60 years or older resident in LTCIs. High quality RCTs are required to avoid the risks of bias in methodology and conduct identified by this review and to test further these interventions in combination.

Read the full abstract...
Background: 

A systematic review found that 3% of working adults who had received influenza vaccine and 5% of those who were unvaccinated had laboratory-proven influenza per season; in healthcare workers (HCWs) these percentages were 5% and 8% respectively. Healthcare workers may transmit influenza to patients.

Objectives: 

To identify all randomised controlled trials (RCTs) and non-RCTs assessing the effects of vaccinating healthcare workers on the incidence of laboratory-proven influenza, pneumonia, death from pneumonia and admission to hospital for respiratory illness in those aged 60 years or older resident in long-term care institutions (LTCIs).

Search strategy: 

We searched CENTRAL (2015, Issue 9), MEDLINE (1966 to October week 3, 2015), EMBASE (1974 to October 2015) and Web of Science (2006 to October 2015), but Biological Abstracts only from 1969 to March 2013 and Science Citation Index-Expanded from 1974 to March 2013 due to lack of institutional access in 2015.

Selection criteria: 

Randomised controlled trials (RCTs) and non-RCTs of influenza vaccination of healthcare workers caring for individuals aged 60 years or older in LTCIs and the incidence of laboratory-proven influenza and its complications (lower respiratory tract infection, or hospitalisation or death due to lower respiratory tract infection) in individuals aged 60 years or older in LTCIs.

Data collection and analysis: 

Two authors independently extracted data and assessed risk of bias. Effects on dichotomous outcomes were measured as risk differences (RDs) with 95% confidence intervals (CIs). We assessed the quality of evidence with GRADE.

Main results: 

We identified four cluster-RCTs and one cohort study (n = 12,742) of influenza vaccination for HCWs caring for individuals ≥ 60 years in LTCIs. Four cluster RCTs (5896 residents) provided outcome data that addressed the objectives of our review. The studies were comparable in their study populations, intervention and outcome measures. The studies did not report adverse events. The principal sources of bias in the studies related to attrition, lack of blinding, contamination in the control groups and low rates of vaccination coverage in the intervention arms, leading us to downgrade the quality of evidence for all outcomes due to serious risk of bias.

Offering influenza vaccination to HCWs based in long term care homes may have little or no effect on the number of residents who develop laboratory-proven influenza compared with those living in care homes where no vaccination is offered (RD 0 (95% CI -0.03 to 0.03), two studies with samples taken from 752 participants; low quality evidence). HCW vaccination probably leads to a reduction in lower respiratory tract infection in residents from 6% to 4% (RD -0.02 (95% CI -0.04 to 0.01), one study of 3400 people; moderate quality evidence). HCW vaccination programmes may have little or no effect on the number of residents admitted to hospital for respiratory illness (RD 0 (95% CI -0.02 to 0.02, one study of 1059 people; low quality evidence). We decided not to combine data on deaths from lower respiratory tract infection (two studies of 4459 people) or all cause deaths (four studies of 8468 people). The direction and size of difference in risk varied between the studies. We are uncertain as to the effect of vaccination on these outcomes due to the very low quality of evidence. Adjusted analyses, which took into account the cluster design, did not differ substantively from the pooled analysis with unadjusted data.

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