Abstract

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

Author(s)

Roger E Thomas, Tom Jefferson, Toby J Lasserson, Stan Earnshaw

Abstract

Plain language summary

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

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.

Author(s)

Roger E Thomas, Tom Jefferson, Toby J Lasserson, Stan Earnshaw

Reviewer's Conclusions

Authors' conclusions 

Implications for practice

The effects of healthcare worker (HCW) vaccination on influenza‐specific outcomes in older residents of long‐term care institutions are uncertain. The four cluster‐randomised controlled trials included in our review are at high risk of bias and are underpowered for influenza (low‐certainty evidence), lower respiratory tract infections (low‐certainty evidence), admissions to hospital (low‐certainty evidence), and deaths from lower respiratory tract illness (very low‐certainty evidence).

We judged the certainty of evidence for the reduction in all‐cause mortality observed with HCW vaccination to be moderate due to risk of bias. We are unable to reconcile the lower rate of all‐cause mortality following HCW vaccination with the lack of a clear effect on influenza morbidity. Influenza deaths are a small part of overall mortality in age groups over 60 and, therefore, all‐cause death rates should be interpreted with caution when considering the impact of influenza vaccination in this group.

Equity‐related implications for practice

We did not perform an equity assessment.

Implications for research

The randomised controlled trials (RCTs) of healthcare worker (HCW) vaccination in long‐term care institutions (LTCIs) have yet to provide a robust evidence base to guide decision‐making. Future RCTs need to take into account the following challenges in the design and implementation of interventions studied, and the conduct of studies in LTCIs.

The clinical and research communities have been waiting a long time for a definitive cluster‐RCT of HCW influenza vaccination in LTCIs. It is important that it is comprehensive and controls for all possible alternative explanations other than HCW vaccination rates for LTCI residents’ influenza illnesses.

• Low HCWs rates of influenza vaccination. Apply existing research on reducing barriers to develop comprehensive evidence‐based interventions involving all hospital staff in both the development and presentation of the interventions. Some LTCIs have higher vaccination rates of > 80%. LTCIs with the lowest rates may need initial individual and group incentives.
• Low rates of influenza vaccination of LCTI residents. Apply existing research on reducing barriers to develop comprehensive evidence‐based interventions involving all hospital staff in both the development and presentation of the interventions. Involve family members and carers. Identify and solve policy, leadership and administrative reasons for LTCIs with low rates. Identify non‐vaccinated residents in the literature and in individual LTCIs, and develop interventions to increase their rates, including vaccine refusers.
• Health systems experience multiple transfers between the community, LTCIs and hospitals and the vaccination status of patients and HCWs in each is important to prevent transfers of infected persons to LTCIs. Home HCWs care for multimorbid elderly patients who may be admitted to an LTCI directly or via a hospital and thus influence influenza rates. The vaccination status of these workers is thus relevant to the overall influenza transmission rate in hospitals. An analysis of a random sample of US national Home Health Care surveys between 2018 and 2019 found that 26% of agencies required staff influenza vaccination and 71% reported staff influenza vaccination rates of ≥ 75%. Half of the agencies provided free vaccinations on site [39].
• Inadequate influenza vaccination rates of elderly people in the community. There is considerable scope for increasing influenza vaccination rates in community‐dwelling older people and the next major study could contemplate a community intervention arm as part of the LTCI cluster‐RCT to increase rates in community‐dwelling older people, so when they are admitted to an LTCI they are vaccinated.
• Quarantine of patients before admittance to LTCIs. The next RCT could consider an intervention arm of quarantining people before admittance to LTCIs.

Implications for research: suggestions for future research designs

Future cluster‐RCTs of influenza vaccination of HCWs should control for known reasons for as many changes as possible in LTCI residents’ influenza rates from environmental and organisational influences, then provide evidence at low risk of bias for each of these PICO criteria.

• Population: all patients, HCWs and visitors to the institutions in the intervention and control groups.
• Interventions in intervention group LTCIs: influenza vaccination of all HCWs (including all staff who share space and air circulation with residents). Frequent monitoring of hand washing and face mask use. Laboratory tests for all HCWs during influenza season and require HCWs with influenza to stop work. Proof of influenza vaccination of all visitors. An experiment in a small simulated ward without patients or staff found that a combination of a positive and negative oxygen ion purifier (PNOI) and a HEPA filter achieved 100% purification rates after 30 minutes against H1N1‐pr8 influenza. Before the major cluster‐RCT is conducted, real‐world experiments in fully staffed wards should be conducted to test filter combinations [40]. Another intervention arm could use a rapid quarantine unit for rapid pathogen testing for new residents and residents transferred from hospital.
• Comparison: LTCIs usual care and influenza vaccination protocol.
• Outcomes: influenza vaccination rates of HCWs and patients. Laboratory testing for pathogens (influenza, respiratory syncytial virus, pneumococcus, SARS, other respiratory pathogens – rhinovirus is a major co‐infection); detailed independent assessment of pre‐hospital and hospital clinical records; comorbidities, laboratory tests (blood cultures, white blood cell counts, other laboratory results) cause of hospitalisation; lower respiratory tract infection (imaging), and cause of death. The cluster‐RCTs included in the current review provided incomplete evidence because they did not provide comprehensive assessments of cause of death (ideally this would be independently conducted by two physicians).

Equity‐related implications for research

The included RCTs were only conducted in France and the UK and not in other countries at different World Health Organization stages of development. No patient characteristics were measured, such as ethnicity or socio‐economic status, and the studies did not include institutions.

Get full text at The Cochrane Library