Adjusted HRs for all-cause mortality and its covariables, subanalysis COVID-19 group (n=4061)
| Covariable | All-cause mortality HR | 95% CI |
| Influenza vaccination in 2019 (yes vs no)* | 1.12 | 0.77 to 1.62 |
| Age group, relative to group 0–59 years | ||
| 60–74 years | 5.54 | 2.35 to 13.06 |
| 75+ years | 23.75 | 10.26 to 54.97 |
| Sex (female vs male) | 0.66 | 0.48 to 0.91 |
| Cardiovascular disease (yes vs no) | 1.88 | 1.35 to 2.62 |
| Diabetes mellitus (yes vs no) | 1.87 | 1.35 to 2.59 |
| Impaired resistance to infections (yes vs no) | 1.84 | 1.09 to 3.10 |
*Presented in table as it contributes to answering the main research question despite an insignificant association.