Effects of infuenza vaccination status in the current and 3 previous seasons in reducing severity of illness in patients who were admitted to hospital for influenza
| Analysis subset | No. of patients with severe influenza/no. of patients with nonsevere influenza | Crude OR (95% CI)* | Adjusted OR (95% CI)* | p value |
|---|---|---|---|---|
| All patients with severe influenza | ||||
| Unvaccinated in the current and previous seasons | 58/189 | Ref. | Ref. | |
| Unvaccinated in the current and vaccinated in any previous season | 25/97 | 0.84 (0.49–1.43) | 0.79 (0.43–1.43) | 0.4 |
| Vaccinated in the current and unvaccinated in previous seasons | 10/21 | 1.55 (0.69–3.48) | 2.22 (0.89–5.51) | 0.09 |
| Vaccinated in the current and any previous season | 37/291 | 0.41 (0.26–0.65) | 0.45 (0.26–0.76) | 0.003 |
| All patients with influenza who were admitted to ICU | ||||
| Unvaccinated in the current and previous seasons | 40/189 | Ref. | Ref. | |
| Unvaccinated in the current and vaccinated in any previous season | 16/97 | 0.78 (0.42–1.46) | 0.74 (0.37–1.50) | 0.4 |
| Vaccinated in the current and unvaccinated in previous seasons | 4/21 | 0.90 (0.29–2.77) | 1.14 (0.34–3.87) | 0.8 |
| Vaccinated in the current and any previous season | 17/291 | 0.28 (0.15–0.50) | 0.35 (0.17–0.70) | 0.003 |
| Patients with influenza who died within 30 d after hospital admission | ||||
| Unvaccinated in the current and previous seasons | 32/189 | Ref. | Ref. | |
| Unvaccinated in the current and vaccinated in any previous season | 19/97 | 1.16 (0.62–2.15) | 1.09 (0.52–2.31) | 0.8 |
| Vaccinated in the current and unvaccinated in previous seasons | 7/21 | 1.97 (0.77–5.51) | 3.35 (1.06–10.58) | 0.04 |
| Vaccinated in the current and any previous season | 25/291 | 0.51 (0.29–0.88) | 0.44 (0.23–0.86) | 0.02 |
Note: CI = confidence interval, ICU = intensive care unit, OR = odds ratio, Ref. = reference.
↵* Estimates were obtained from unconditional logistic regression models. The adjusted models included sex, age, number of chronic conditions, Barthel Index score, number of visits to primary care and hospital in the previous year, pneumococcal vaccination, pneumonia diagnosis in the previous 2 yr, oral corticosteroid treatment in the previous month, influenza season and hospital site.