Study	Reason for exclusion
Amodio 2014	ILI. Data influenza seasons 2005‐2012 in Italian acute care hospital were analysed retrospectively. Hospital discharge records; HCW influenza vaccination, ILI in the general population. 62,343 hospitalised patients, 185 (0.03%) nosocomial ILI. HCW influenza vaccination coverage declined from 13.2% to 3.1% (P value < 0.001)
Bellei 2007	Surveillance study of influenza and rhinovirus infections among HCWs; no vaccination data; no data for elderly people
Bertin 2007	Intranet assessment of HCW vaccination status; no vaccination or outcome data for elderly people
Bénet 2012	Study of "influenza‐like illness" in a 1000 bed acute care hospital in Lyon, France. 12 short‐stay units with 224 beds participated in 2004‐5, 29 with 493 beds in 2005‐6, and 30 with 537 beds in 2006‐7. Nurses visited participating wards daily to search for patients with ILI (defined as temperature ≥ 37.8°C, cough or sore throat, and no use of antipyretics) then a nasal swab was tested for influenza by RT‐PCR, ELISA and culture. Cannot separate outcomes for those > 60
Carusone 2007	Study of pneumonia and lower respiratory infections in nursing home residents as predictors of hospitalisation and mortality; based on previous RCT; influenza vaccination status of patients; no HCW vaccination data
Chicaíza‐Becerra 2008	Economic evaluation of influenza vaccination of HCWs; no vaccination or outcome data for elderly people
Chittaro 2009	Influenza vaccination campaign for HCWs; no data on elderly people
del Villar‐Belzunce 2007	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Doratotaj 2008	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Enserink 2011	Study of 18 long‐term care facilities in the Netherlands in which GPs and nurse practitioners reported ILI cases. They did not use the WHO or CDC ILI definitions but required sudden onset and one symptom (fever or febrile feeling, malaise, headache, sore throat or shortness of breath). These criteria include many respiratory illnesses. They compared patient ILI incidence in facilities with < 15% and ≥ 15% HCW vaccination, December 2008‐April 2009. There were "no institutional influenza outbreaks" but "ILI was frequently diagnosed." This absence of outbreaks implies that their ILI measure did not measure influenza. Nevertheless, they computed an adjusted rate ratio for patient ILI rates = 0.3 (95% CI 0.1 to 1.2).
Hood 2009	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Isaacs 1997	Data were not presented by HCW vaccine coverage; only 21% of staff were vaccinated; amantadine was a confounder as it was given to patients and not staff; a flow sheet of admissions and discharges was not presented
Isahak 2007	Programme to increase influenza vaccination among elderly people in long‐term care homes; no vaccination data for HCWs
Kheok 2008	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Kimura 2007	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Landi 2006	Prospective observational study of influenza vaccination in elderly people; no HCW data
Lee 2008	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Looijmans‐van den Akker 2007	Survey of effect of national policy on influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Mangtani 2004	Historical cohort study of individuals older than 64 years in the UK General Practice Research Database 1989 to 1999 in England and Wales. No intervention for HCWs
Munford 2008	Campaign to increase influenza vaccination among elderly people and HCWs; no outcome data for elderly people
Riphagen‐Dalhuisen 2013	RCT. Randomised 6 university medical centres in the Netherlands to either receive a programme to increase staff influenza vaccination rates or pursue their usual vaccination policy. The effect on patient morbidity was a secondary goal, limited to the internal medicine and pediatrics wards and patient outcome data were collected retrospectively from charts, laboratory records and discharge letters. Cannot separate outcomes for patients > 60
Sato 2005	Study of antibody levels in elderly people and HCWs in response to influenza vaccination
Shugarman 2006	Retrospective cross‐sectional study of 344 nursing homes (310 replied) from one chain in the US, with reports of staff and resident vaccination rates and whether the home had an ILI cluster (≥ 3 residents with ILI within 72 hours)
Wendelboe 2011	75 long‐term care facilities in New Mexico, US, during the influenza seasons of 2006‐7 and 2007‐8. 12% (9 homes) provided no reports in 2006‐7 and 18% (which computes as 13.5 homes!) no reports in 2007‐8. However, data are presented for all 75 homes (15 homes which had an outbreak and 50 which had none). An influenza outbreak was defined as a single patient case. Cases were diagnosed by viral culture or a rapid antigen test The authors noted that: "The ecologic study design limits our ability to control for certain characteristics such as the distribution of residents’ ages and the presence of comorbidities… For example, it is possible that certain facilities cared for residents in poorer health, which likely resulted in those patients who were vaccinated against influenza being less effectively protected from influenza by vaccination." The authors also noted that: "Another potential limitation is that we restricted our surveillance to HCWs with direct patient care. Future surveillance systems may find it helpful to include all healthcare personnel (including clerical, dietary, housekeeping, maintenance, and volunteer personnel)…" There were no data on the total number of patients during the 2 years. The odds of an "outbreak" were paradoxically higher with resident vaccination rates of 91% to 100% compared to 0% to 90% (OR 4.85, 95% CI 1.17 to 20.18) implying more vulnerable patients were more likely to be vaccinated. The authors computed an adjusted OR of 0.76 (0.62 to 0.93) for a reduction in "outbreaks" for a 10% increase in HCW vaccination. However, with only 21 cases and an unknown denominator it is inappropriate to place weight on the odds ratios computed for the effects of HCW vaccination. This is not a RCT and is subject to unmeasured confounders such as a superior LCT culture, which limits the transmission of influenza by hand‐washing, quarantining patients and limiting visitors
Yang 2007	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people
Yassi 1993	Data were not presented by HCW vaccine coverage. Vaccine and amantadine were used to control outbreak: amantadine acts as confounder
Zimmerman 2009	Programme to increase influenza vaccination among HCWs; no vaccination or outcome data for elderly people

CDC: Centers for Disease Control and Prevention
 CI: confidence interval
 ELISA: enzyme‐linked immunosorbent assay
 HCW: healthcare worker
 ILI: influenza‐like illness
 OR: odds ratio
 RCT: randomised controlled trial
 RT‐PCR: reverse‐transcriptase polymerase chain reaction
 WHO: World Health Organization