Table 1.
Characteristics of the Study Population According to Immunization Status
| Study Population | Total Study Population CY = 11,493 | Immunized in Current Year but No Prior IIV Immunization CY = 2,914 | Immunized in Current Year and 1 IIV in Previous 2 Years CY = 2,450 | Immunized in Current Year and ≥2 IIVs in Previous 3 Years, Including Prior Year CY = 4,653 |
|---|---|---|---|---|
| Sex (%) | ||||
| Boys | 57.9 | 57.7 | 57.1 | 57.6 |
| Girls | 42.1 | 42.3 | 42.9 | 42.4 |
| Socioeconomic status score | ||||
| Low | 16.4 | 17.0 | 16.1 | 14.6 |
| Middle | 50.7 | 48.5 | 50.2 | 54.3 |
| High | 32.7 | 34.5 | 33.5 | 31.0 |
| Age group, y (%) | ||||
| 0-5 | 8.4 | 20.9 | 8.8 | 1.2 |
| 6-10 | 15.6 | 20.2 | 19.0 | 10.5 |
| 11-15 | 45.3 | 37.5 | 44.7 | 48.3 |
| >15 | 30.7 | 21.7 | 27.6 | 39.9 |
| Health care–seeking behavior; number of consultations (%) | ||||
| 0 | 90.3 | 88.7 | 90.4 | 92.0 |
| 1 | 6.8 | 8.1 | 6.7 | 5.5 |
| >1 | 2.9 | 3.2 | 2.8 | 2.6 |
| Out-season RIs in previous year (%) | ||||
| 0 | 96.5 | 96.4 | 97.4 | 98.1 |
| 1 | 3.0 | 3.2 | 2.4 | 1.5 |
| >1 | 0.5 | 0.3 | 0.2 | 0.3 |
| Indicated diseases; % yes | ||||
| Preexisting cardiovascular disease | 10.7 | 10.5 | 10.0 | 10.2 |
| Chronic lung disease | 78.0 | 79.7 | 77.3 | 78.5 |
| Diabetes | 8.3 | 6.3 | 8.5 | 9.2 |
| Chronic kidney disorder | 0.1 | 0.1 | 0.1 | 0.1 |
| Immunocompromising condition | 3.9 | 3.7 | 4.6 | 3.3 |
| Respiratory difficulties with neurologic origin | 1.7 | 1.3 | 1.8 | 1.8 |
| Number of indications for IIV (%) | ||||
| 1 | 97.4 | 98.3 | 97.7 | 96.8 |
| >1 | 2.6 | 1.7 | 2.3 | 3.2 |
| Incidence of RI during influenza season/100 child-years (95% CI) | ||||
| All ages | 18.4 (17.1-19.8) | 27.8 (24.7-31.2) | 13.1 (10.8-15.7) | 13.4 (11.7-15.4) |
| 0-5 y | 56.4 (48.6-65.1) | 66.2 (55.6-78.2) | 37.9 (25.5-54.4) | 49.4 (24.1-90.8) |
| 6-10 y | 30.3 (26.0-35.0) | 30.0 (23.0-38.4) | 22.8 (16.1-31.3) | 26.9 (19.7-35.9) |
| 11-15 y | 13.2 (11.5-15.0) | 14.8 (11.3-19.1) | 9.4 (6.6-12.9) | 12.4 (9.7-14.8) |
| >15 y | 9.6 (7.9-11.6) | 12.6 (8.5-18.1) | 4.5 (2.3-8.0) | 10.4 (8.1-13.2) |
| Boys | 19.3 (17.6-21.3) | 30.0 (25.7-34.7) | 14.7 (11.5-18.5) | 13.8 (11.5-16.5) |
| Girls | 17.1 (15.1-19.2) | 24.8 (20.4-29.9) | 10.9 (7.7-14.9) | 12.9 (10.3-15.9) |
| Number of consultations for RI during influenza season (%) | ||||
| 0 | 95.2 | 93.0 | 96.5 | 96.3 |
| 1 | 3.0 | 3.9 | 2.3 | 2.5 |
| >1 | 1.8 | 3.1 | 1.2 | 1.2 |
CY = child years; IIV = inactivated influenza vaccine; RI = respiratory illness.