Table 3. Stratified analyses presenting hazard ratios with 95% confidence intervals and vaccine effectiveness estimates for seasonal influenza vaccination on influenza outcome among individuals with comorbidity, Stockholm County, influenza seasons 2011/12–2014/15.
| Category | Total number | All cases among those with comorbidity | Outpatient among those with comorbidity | Inpatient among those with comorbidity | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Cases | HR (95% CI) | VE | Cases | HR (95% CI) | VE | Cases | HR (95% CI) | VE | ||
| 2011/12 | ||||||||||
| All | ||||||||||
| Unvaccinated | 438,274 | 1,624 | Ref | NA | 1,424 | Ref | NA | 200 | Ref | NA |
| Vaccinated | 148,196 | 307 | 0.79 (0.66–0.95) | 21% (5–34) | 164 | 0.71 (0.57–0.90) | 14% (0.36) | 143 | 0.90 (0.65–1.24) | 10% (0–35) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 8,205 | 193 | Ref | NA | 103 | Ref | NA | 90 | Ref | NA |
| Vaccinated | 131,456 | 249 | 0.85 (0.66–1.09) | 15% (0–34) | 117 | 0.87 (0.61–1.23) | 13% (0–39) | 132 | 0.83 (0.60–1.18) | 17% (0–40) |
| 2012/13 | ||||||||||
| All | ||||||||||
| Unvaccinated | 475,163 | 949 | Ref | NA | 607 | Ref | NA | 342 | Ref | NA |
| Vaccinated | 138,020 | 117 | 0.54 (0.41–0.70) | 46% (30–59) | 36 | 0.56 (0.35–0.89) | 44% (11–65) | 81 | 0.50 (0.36–0.69) | 50% (31-64) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 106,110 | 180 | Ref | NA | 47 | Ref | NA | 133 | Ref | NA |
| Vaccinated | 123,472 | 94 | 0.47 (0.34–0.64) | 53% (37–66) | 24 | 0.51 (0.27–0.95) | 49% (5–73) | 70 | 0.47 (0.33–0.67) | 53% (33–67) |
| 2013/14 | ||||||||||
| All | ||||||||||
| Unvaccinated | 488,048 | 745 | Ref | NA | 604 | Ref | NA | 141 | Ref | NA |
| Vaccinated | 147,899 | 93 | 0.70 (0.51–0.95) | 30% (5-49) | 51 | 0.81 (0.54–1.21) | 19% (0–46) | 42 | 0.52 (0.32–0.84) | 48% (16–68) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 108,496 | 104 | Ref | Ref | 37 | Ref | Ref | 67 | Ref | Ref |
| Vaccinated | 130,592 | 67 | 0.55 (0.37–0.82) | 45% (18-63) | 30 | 0.78 (0.41–1.48) | 22% (0–59) | 37 | 0.45 (0.27–0.75) | 55% (25–73) |
| 2014/15 | ||||||||||
| All | ||||||||||
| Unvaccinated | 501,421 | 2,002 | Ref | Ref | 1,391 | Ref | Ref | 611 | Ref | Ref |
| Vaccinated | 151,827 | 731 | 0.85 (0.75–0.97) | 15% (3-25) | 237 | 0.84 (0.68–1.03) | 16% (0–32) | 494 | 0.85 (0.72–1.00) | 15% (0–28) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 113,444 | 591 | Ref | NA | 164 | Ref | NA | 427 | Ref | NA |
| Vaccinated | 133,226 | 639 | 0.82 (0.71–0.94) | 18% (6-29) | 169 | 0.84 (0.63–1.11) | 16% (0–37) | 470 | 0.82 (0.69–0.97) | 18% (3-31) |
CI: confidence interval; HR: hazard ratios; NA: not applicable; Ref: reference value; VE: vaccine effectiveness
International Classification of Diseases, 10th revision codes J09–J11 were used to identify influenza diagnoses. [10]
a Vaccine effectiveness, calculated (1 − HR × 100).
b Hazard ratios derived from Cox proportional hazards regression model; adjusted for sex, age (age groups 10 years intervals), socioeconomic status, previous seasonal vaccination, pneumococcal vaccination and Pandemrix vaccination. As complete case analysis was used, the number of cases decreased due to missing in socioeconomic status.