Table 4.
Incidence of influenza complications and odds ratios (ORDR) for influenza vaccination
| Age | 1–64 years | 1–4 years | 5–12 years | 13–19 years | 20–64 years |
|---|---|---|---|---|---|
| No. (%) | No. (%) | No. (%) | No. (%) | No. (%) | |
| Outcome | ORDR (95% CI) | ORDR (95% CI) | ORDR (95% CI) | ORDR (95% CI) | ORDR (95% CI) |
| Hospitalization with influenza a | 149 (0.04) | 76 (0.2) | 51 (0.1) | 4 (0.01) | 20 (0.01) |
| 0.709 (0.429–0.988) | 0.529 (0.237–0.821) | 0.724 (0.199–1.248) | 5.547 (−6.851–17.945) | 1.153 (−0.040–2.346) | |
| Pneumonia b | 5025 (1.4) | 2492 (5.2) | 1354 (1.4) | 197 (0.4) | 990 (0.6) |
| 0.437 (0.405–0.469) | 0.439 (0.396–0.483) | 0.368 (0.313–0.422) | 0.531 (0.340–0.722) | 0.413 (0.337–0.489) | |
| Respiratory tract diseases c | 180,177 (50.1) | 40,303 (89.5) | 62,499 (69.2) | 21,269 (43.0) | 57,240 (32.5) |
| 0.612 (0.603–0.621) | 0.436 (0.407–0.464) | 0.449 (0.434–0.464) | 0.506 (0.483–0.529) | 0.607 (0.591–0.623) | |
| Hospitalization with respiratory tract diseases d | 1594 (0.4) | 952 (2.0) | 308 (0.3) | 55 (0.1) | 290 (0.2) |
| 0.441 (0.386–0.497) | 0.491 (0.415–0.567) | 0.303 (0.211–0.394) | 0.314 (0.062–0.566) | 0.356 (0.232–0.479) | |
| Emergency hospitalization with influenza or pneumonia e | 59 (0.02) | 10 (0.02) | 9 (0.01) | 5 (0.01) | 35 (0.02) |
| 0.403 (0.126–0.680) | 0.935 (−0.340–2.210) | 0.122 (−0.083–0.328) | 0.020 (− 0.009–0.048) | 0.611 (0.062–1.160) |
For each outcome, we excluded subjects who had the outcome within 13 days after vaccination. The number of study subjects in an age strata differed by outcome because vaccinees experiencing an outcome before vaccination were censored at the outcome onset and classified as non-vaccinees. All confounders were adjusted using a doubly robust method. Preceding onset of influenza among family members was included only for the analysis of “hospitalization with influenza” outcome
a Hospitalization started within 3 days before or after the data of influenza diagnosis codes
b Pneumonia including the ICD-10 codes J12-J18
c Respiratory tract disease including the ICD-10 codes J00-J22, except for influenza diagnosis codes, J10 and J11
d Hospitalization started within 7 days after diagnosis of respiratory tract diseases other than influenza
e Emergency hospitalization with diagnoses of influenza or pneumonia