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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.