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

Rationale: People who work in long-term care institutions (LTCIs), such as doctors, nurses, other health professionals, cleaners and porters (and also family visitors), may have substantial rates of influenza during influenza seasons. They often continue to work when infected with influenza, increasing the likelihood of transmitting influenza to those in their care. The immune systems of care home residents may be weaker than those of the general population; vaccinating care home workers could reduce transmission of influenza within LTCIs.

Objectives: To assess the effects of vaccinating healthcare workers in long-term care institutions against influenza on influenza-related outcomes in residents aged 60 years or older.

Search methods: We searched the Cochrane Central Register of Controlled Trials (via Cochrane Library), MEDLINE (via Ovid), Embase (via Elsevier), Web of Science (Science Citation Index-Expanded and Conference Proceedings Citation Index - Science), and two clinical trials registries up to 22 August 2024.

Eligibility criteria: In this version of the review we restricted eligibility to randomised controlled trials (RCTs) of influenza vaccination of healthcare workers (HCWs) caring for residents aged 60 years or older in LTCIs. Previously we included cohort or case-control studies.

Outcomes: Outcomes of interest were: influenza (confirmed by laboratory tests) and its complications (lower respiratory tract infection; hospitalisation or death due to lower respiratory tract infection), all-cause mortality, and adverse events.

Risk of bias: We used version one of the Cochrane risk of bias tool for RCTs.

Synthesis methods: Two review authors independently extracted data and assessed the risk of bias. We used risk ratios (RRs) with 95% confidence intervals (CIs) to summarise the effects of vaccination on our outcomes of interest. We accounted for clustering by dividing events and sample sizes for each study by an assumed design effect as part of a sensitivity analysis. We used GRADE to assess the certainty of evidence for our outcomes of interest.

Included studies: We did not identify any new trials for inclusion in this update. Four cluster-RCTs from Europe (8468 residents) of interventions to offer influenza vaccination for HCWs caring for residents ≥ 60 years in LTCIs provided outcome data that addressed the objectives of our review. The average age of the residents was between 77 and 86 years, and most were female (70% to 77%). The studies were comparable in their 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 certainty of evidence for all outcomes due to serious risk of bias.

Synthesis of results: Offering influenza vaccination to HCWs based in LTCIs may have little or no effect on the number of residents who develop influenza compared with those living in care homes where no vaccination is offered (from 5% to 4%) (RR 0.87, 95% CI 0.46 to 1.63; 2 studies, 752 participants; low-certainty evidence). We rated the evidence to be low from one study of 1059 residents showing a slight reduction in lower respiratory tract infection from HCW vaccination (6% versus 4%) (RR 0.70, 95% CI 0.41 to 1.2). The confidence interval is compatible with both a meaningful reduction and a slight increase in infections when illustrated as an absolute effect; 2% to 7%. Taking account of clustering for this outcome increased the confidence interval further, and we rated the evidence as very low-certainty accordingly (RR 0.72, 95% CI 0.28 to 1.85). HCW vaccination programmes may have little or no effect on the number of residents admitted to hospital for respiratory illness (RR 1.02, 95% CI 0.82 to 1.27; 1 study, 3400 participants; low-certainty evidence). There is insufficient evidence to determine whether HCW vaccination impacts on death due to lower respiratory tract infections in residents: 2% of residents in both groups died from lower respiratory tract infections based on the RR of 0.82 (95% CI 0.45 to 1.49; 2 studies, 4459 participants; very low-certainty evidence). HCW vaccination probably leads to a reduction in all-cause deaths from 9% to 6% (RR 0.69, 95% CI 0.60 to 0.80; 4 studies, 8468 participants; moderate-certainty evidence).

Authors' conclusions: The effects of HCW vaccination on influenza-specific outcomes in older residents of LTCIs are uncertain. The reduction in all-cause mortality in people observed could not be explained by changes in influenza-specific outcomes. This review did not find information on co-interventions with HCW vaccination: hand washing, face masks, early detection of laboratory-proven influenza, quarantine, avoiding admissions, antivirals and asking HCWs with influenza or influenza-like illness not to go to work. Better studies are needed to give greater certainty in the evidence for vaccinating HCWs to prevent influenza in residents aged 60 years or older in LTCIs. Additional studies are needed to further test these interventions in combination.

Funding: This review update received no dedicated funding. Previous versions of this review were supported by grants from the National Institute of Health Research (UK), and the National Health and Medical Research Council (Australia).

Registration: Protocol (2005): 10.1002/14651858.CD005187.pub Original review (2006): 10.1002/14651858.CD005187.pub2 Update (2010): 10.1002/14651858.CD005187.pub3 Update (2013): 10.1002/14651858.CD005187.pub4 Update (2016): 10.1002/14651858.CD005187.pub5.