Table 4. Hazard ratios with 95% confidence intervals and vaccine effectiveness estimates for seasonal influenza vaccination on pneumonia outcome including inpatient and outpatient cases, Stockholm County, influenza seasons 2011/12–2014/15.
| Category | Total number | All cases | Outpatient | Inpatient | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Cases | HRa (95% CI) | VEb | Cases | HRa (95% CI) | VEb | Cases | HRa (95% CI) | VEb | ||
| 2011/12 | ||||||||||
| All | ||||||||||
| Unvaccinated | 1,884,818 | 20,088 | Ref | NA | 15,123 | Ref | NA | 4,965 | Ref | NA |
| Vaccinated | 204,229 | 4,849 | 1.15 (1.09–1.20) | 0 | 2,267 | 1.28 (1.20–1.37) | 0 | 2,582 | 0.97 (0.90–1.07) | 3% (0–10) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 141,097 | 4,735 | Ref | NA | 1,878 | Ref | NA | 2,857 | Ref | NA |
| Vaccinated | 175,668 | 4,333 | 0.93 (0.88–0.99) | 7% (1–12) | 1,946 | 1.14 (1.04–1.24) | 0 | 2,387 | 0.82 (0.76–0.88) | 18% (12–24) |
| 2012/13 | ||||||||||
| All | ||||||||||
| Unvaccinated | 1,936,790 | 10,224 | Ref | NA | 8,013 | Ref | NA | 2,211 | Ref | NA |
| Vaccinated | 184,679 | 3,606 | 1.02 (0.96–1.07) | 0 | 1,518 | 1.05 (0.97–1.13) | 0 | 2,088 | 0.97 (0.90–1.04) | 3% (0–10) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 164,807 | 4,697 | Ref | NA | 1,787 | Ref | NA | 2,910 | Ref | NA |
| Vaccinated | 161,859 | 3,250 | 0.95 (0.89–1.00) | 5% (0–11) | 1,319 | 1.05 (0.96–1.16) | 0 | 1,931 | 0.89 (0.83–0.96) | 11% (4–17) |
| 2013/14 | ||||||||||
| All | ||||||||||
| Unvaccinated | 1,972,363 | 12,718 | Ref | NA | 8,527 | Ref | NA | 4,191 | Ref | NA |
| Vaccinated | 198,844 | 3,737 | 1.05 (1.00–1.11) | 0 | 1,700 | 1.20 (1.11–1.29) | 0 | 2,037 | 0.95 (0.88–1.03) | 5% (0–12) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 166,773 | 4,247 | Ref | NA | 1,633 | Ref | NA | 2,614 | Ref | NA |
| Vaccinated | 170,003 | 3,349 | 1.00 (0.94–1.06) | 0 | 1,455 | 1.20 (1.09–1.32) | 0 | 1,894 | 0.89 (0.82–0.96) | 11% (4-18) |
| 2014/15 | ||||||||||
| All | ||||||||||
| Unvaccinated | 2,002,587 | 16,155 | Ref | NA | 11,336 | Ref | NA | 4,819 | Ref | NA |
| Vaccinated | 204 585 | 4 636 | 1.08 (1.03–1.13) | 0 | 2,207 | 1.17 (1.09–1.25) | 0 | 2,429 | 0.97 (0.91–1.04) | 3% (0–9) |
| Age ≥ 65 years | ||||||||||
| Unvaccinated | 166 773 | 5 264 | Ref | NA | 2,221 | Ref | NA | 3,043 | Ref | NA |
| Vaccinated | 173 170 | 4 146 | 0.98 (0.93–1.03) | 2% (0–7) | 1,905 | 1.12 (1.03–1.22) | 0 | 2,241 | 0.89 (0.82–0.95) | 11% (5–18) |
CI: confidence interval; HR: hazard ratio; NA: not applicable; Ref: reference value; VE: vaccine effectiveness.
International Classification of Diseases, 10th revision codes J12-J18 were used to identify non-influenza pneumonia diagnoses [10].
a Hazard ratios derived from Cox proportional hazards regression model; confidence interval; adjusted for sex, age (age groups 10 years intervals), comorbidity status, 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.
b Vaccine effectiveness calculated (1 – HR × 100).