Key messages
Offering flu vaccination to people working in care institutions may make little or no difference to the number of residents who get flu or go to hospital with a chest infection, compared to those living in care institutions where no vaccination is offered.
Although we found that healthcare worker vaccination programmes led to fewer deaths due to any cause in residents of care institutions, we could not explain these results in terms of the reduction in flu or complications from chest infections.
What is flu?
Flu is a respiratory illness. It is spread by a family of viruses and can affect people of all ages. Residents in long-term care institutions (LTCIs) are at a particularly high risk of being unwell with flu because their immune systems are weaker than people who live at home. People who work in LTCIs, such as doctors, nurses, other health professionals, cleaners and porters, may be exposed to flu during flu seasons. They often continue to work when they are infected with different respiratory viruses. This increases the likelihood of spreading them to those in their care. The signs and symptoms of flu are similar to those of many other respiratory illnesses. Therefore, it is important to test the effects of flu vaccination to prove by laboratory tests, which are highly accurate, whether residents in LTCIs actually have flu or another respiratory illness.
What did we want to find out?
We wanted to know if vaccinating healthcare workers against flu reduces the risk of flu and its complications in older residents in LTCIs.
What did we do?
We summarised existing research comparing different strategies to reduce flu in LTCIs. We looked for research studies which randomly assigned different care facilities to invite healthcare workers to receive flu vaccine at the start of the flu season or not.
What did we find?
We identified four studies which included data from 8468 residents. Healthcare workers from care homes in France and the UK were randomly assigned to be offered a flu vaccination. The studies provided information on flu, chest infections, hospital admission for a chest infection, and death. We were unable to identify information about unwanted effects in the studies. The average age of the care home residents was between 77 and 86 years, and the majority were female (between 70% and 77%).
Offering flu vaccination to healthcare workers who care for those aged 60 or over in LTCIs may have little or no effect on flu. We have little confidence in the effects of healthcare worker vaccination programmes on the number of residents with chest infections or the number of residents admitted to hospital due to chest infections. We have very little confidence in the evidence for the number of residents who died from chest infections. Although the number of residents who died from any cause was lower after healthcare worker vaccination, a reduction from 9% to 6%, we could not explain this effect in terms of changes to the number of people with flu or complications from chest infection.
What are the limitations of the evidence?
We were mainly concerned about how people were followed up, the impact of people in the studies being aware of whether they were vaccinated, the use of interventions in the control groups, and low rates of vaccination in the studies. In two studies, data could not be included from everyone who was recruited and this reduced our confidence in the results from those studies. 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 flu, quarantine, avoiding new admissions, prompt antiviral use, asking healthcare workers with a flu-like illness not to go to work).
How up to date is this evidence?
The evidence is current to 22 August 2024.
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.
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.
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.
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.
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.
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.
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.
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).
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