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Table 1 Characteristics of Japanese subjects in the primary analysis

From: Influenza vaccination effectiveness for people aged under 65 years in Japan, 2013/2014 season: application of a doubly robust method to a large-scale, real-world dataset

Characteristics by age group Vaccinee Non-vaccinee P Value a
1–64 years
 N 145,784 223,641  
 Age (median [interquartile range]) 14 [7, 39] 22 [10, 43] < 0.001
 Female 64,914 (44.5%) 98,589 (44.1%) 0.008 *
 Vaccination in the 2012/2013 season 91,541 (62.8%) 20,050 (9.0%) < 0.001 *
 Insured persons (vs dependents) b 45,859 (31.5%) 79,394 (35.5%) < 0.001 *
 Number of children aged 0 to 15 years in a family (median [interquartile range]) c 1 [0, 1] 1 [0, 1] < 0.001
Before influenza season
 Number of outpatient visits
  During office hours (median [range]) 2 [0–118] 1 [0–112] < 0.001
  Outside office hours (median [range]) 0 [0–57] 0 [0–61] < 0.001
 Emergency hospitalization 151 (0.1%) 348 (0.2%) < 0.001 *
 High-risk condition 34,792 (23.9%) 43,735 (19.6%) < 0.001 *
During influenza season
 Preceding onset of influenza in family members 27,817 (19.1%) 38,620 (17.3%) < 0.001 *
1–4 years
 N 23,534 24,101  
 Age (median [interquartile range]) 3 [2, 4] 2 [2, 3] < 0.001
 Female 11,387 (48.4%) 11,809 (49.0%) 0.184 *
 Vaccination in the 2012/2013 season 14,561 (61.9%) 2620 (10.9%) < 0.001 *
 Insured persons (vs dependents) b
 Number of children aged 0 to 15 years in a family (median [interquartile range]) c 1 [1, 1] 1 [1, 1] 0.005
Before influenza season
 Number of outpatient visits
  During office hours (median [range]) 5 [0–92] 4 [0–65] < 0.001
  Outside office hours (median [range]) 0 [0–19] 0 [0–16] < 0.001
 Emergency hospitalization 15 (0.1%) 25 (0.1%) 0.155 *
 High-risk condition 7335 (31.2%) 7451 (30.9%) 0.552 *
During influenza season
 Preceding onset of influenza in family members 5095 (21.6%) 5452 (22.6%) 0.011 *
5–12 years
 N 43,535 50,247  
 Age (median [interquartile range]) 8 [6, 10] 9 [7, 11] < 0.001
 Female 21,215 (48.7%) 24,227 (48.2%) 0.116 *
 Vaccination in the 2012/2013 season 33,310 (76.5%) 6118 (12.2%) < 0.001 *
 Insured persons (vs dependents) b
 Number of children aged 0 to 15 years in a family (median [interquartile range]) c 1 [1, 2] 1 [1, 2] < 0.001
Before influenza season
 Number of outpatient visits
  During office hours (median [range]) 3 [0–85] 2 [0–73] < 0.001
  Outside office hours (median [range]) 0 [0–22] 0 [0–53] < 0.001
 Emergency hospitalization 24 (0.1%) 25 (0.05%) 0.776 *
 High-risk condition 10,193 (23.4%) 9589 (19.1%) < 0.001 *
During influenza season
 Preceding onset of influenza in family members 10,424 (23.9%) 13,024 (25.9%) < 0.001 *
13–19 years
 N 18,123 31,993  
 Age (median [interquartile range]) 14 [13, 15] 15 [14, 16] < 0.001
 Female 8811 (48.6%) 15,536 (48.6%) 0.904 *
 Vaccination in the 2012/2013 season 11,162 (61.6%) 4862 (15.2%) < 0.001 *
 Insured persons (vs dependents) b 158 (0.9%) 327 (1.0%) 0.107 *
 Number of children aged 0 to 15 years in a family (median [interquartile range]) c 1 [0, 1] 1 [0, 1] < 0.001
Before influenza season
 Number of outpatient visits
  During office hours (median [range]) 1 [0–74] 1 [0–61] < 0.001
  Outside office hours (median [range]) 0 [0–20] 0 [0–21] < 0.001
 Emergency hospitalization 15 (0.1%) 47 (0.1%) 0.066 *
 High-risk condition 2219 (12.2%) 3044 (9.5%) < 0.001 *
During influenza season
 Preceding onset of influenza in family members 3479 (19.2%) 6094 (19.0%) 0.688 *
20–64 years
 N 60,591 117,019  
 Age (median [interquartile range]) 42 [35, 50] 42 [34, 50] < 0.001
 Female 23,501 (38.8%) 47,013 (40.2%) < 0.001 *
 Vaccination in the 2012/2013 season 32,508 (53.7%) 6168 (5.3%) < 0.001 *
 Insured persons (vs dependents) b 45,701 (75.4%) 78,797 (67.3%) < 0.001 *
 Number of children aged 0 to 15 years in a family (median [interquartile range]) c 0 [0, 2] 0 [0, 1] < 0.001
Before influenza season
 Number of outpatient visits
  During office hours (median [range]) 1 [0–118] 1 [0–112] < 0.001
  Outside office hours (median [range]) 0 [0–57] 0 [0–76] < 0.001
 Emergency hospitalization 96 (0.2%) 250 (0.2%) 0.013 *
 High-risk condition 15,044 (24.8%) 23,525 (20.1%) < 0.001 *
During influenza season
 Preceding onset of influenza in family members 8819 (14.6%) 13,929 (11.9%) < 0.001 *
  1. Subjects were stratified by age-group and vaccination status in the 2013/2014 influenza season
  2. aThe χ2 test was used for categorical variables (*) and the Mann-Whitney test for continuous variables (†) between vaccinees and non-vaccinees in the 2013/2014 influenza season
  3. bAll children aged under 18 years were treated as dependents
  4. cNumber of other dependents aged 0 to 15 years covered by the same insurance number