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Table 1 Characteristics of included studies on influenza vaccine effectiveness in diabetic patients

From: Vaccines for the prevention of seasonal influenza in patients with diabetes: systematic review and meta-analysis

Author Study design, year Country Age in years (mean or range) Percentage male Identification of diabetic patients Predominantly circulating influenza (sub)strains Study size (n)
Cohort studies        
Hak [29] Prospective, 1996/1997 and 1997/1998 US ≥65, but not reported for diabetic sub-cohort Not reported for diabetic sub-cohort ICD-9 codes, database of managed care organizations A(H3N2) in both seasons 14,915 in 96/97
21,991 in 97/98
Heymann [21] Retrospective, 2000/2001 Israel Vacc., 72.8 ± 0.6 Vacc., 51.8 ICD-9 codes, diabetes register of healthcare service Not reported 16,383
Non-vacc., 73.1 ± 0.5 Non-vacc., 42.1
Isotani [31] Retrospective, 1999/2000 Japan Not reported Not reported Outpatient clinic, unclear Influenza A 450
Rodriguez-Blanco [32] Retrospective, 2002–2005 Spain Vacc., 75.2 ± 6.5 Vacc., 39.8 ICD-9 codes, clinical records A(H3N2) 2,650
Non-vacc., 73.1 ± 6.9 Non-vacc., 42.2
Selvais [33] Prospective, 1995/96 Belgium 56.3 ± 15.9 years 55 Diabetes clinic, unclear Not reported 432
Schade [34] Retrospective, 1995–1997 US 65 to 114 years Not reported ICD-9 codes, hospital discharge Not reported 26,443 in 96/97
23,839 in 97/98
Case–control studies       
Colquhoun [36] not matched, 1989 and 1993 UK ≤19–85 years Cases, n = 59 ICD-9 codes, diabetes register 1989, A(H3N2) 114 (37 cases, 77 controls)
Controls, n = 55 1993, A(H3N2) and B
Gasparini [37] Matched, 2010/11 Italy Not reported for diabetic sub-cohort Not reported for diabetic sub-cohort ICD-9 codes, hospital discharge A(H1N1)pdm, and B 78 (46 cases, 32 controls)
Lau2 [35] Nested, 2000–2008 Canada Working-age, 53 Working age, 52 elderly, 47 ICD-9/10 codes, administrative database Not reported 91,605
Elderly, 741
Looijmans [38] Nested, 1999/2000 Netherlands Cases, 68.1 ± 13.7 Cases, 51.6 controls, 38.3 ICPC codes, general practitioners A(H3N2) 1,753 (192 cases, 1,561 controls)
Controls, 69.8 ± 12.6
Wang [39] Nested, 2001–2009 Taiwan Vacc., 73.1 ± 5.9 Vacc, 50.0 ICD-9 codes, NHRI-database Not reported 9,025 (4,571 vacc., 4,454 non-vacc.)
Non-vacc., 73.2 ± 6.8 Non-vacc., 49.5
Total population       170,924 3
  1. 1Median; 2Published as cohort study, however, due to matching of controls, this study was considered as case–control study here; 3Since overlapping of the study population reported by Hak et al. and Schade et al. for two influenza seasons cannot be ruled out for calculation of the total population for each study numbers of only one season were used.
  2. ICD, International classification of diseases codes; ICPC, International Classification of Primary Care Codes; NHRI, Claims data from the National Health Research Institutes Database.