Table 2. Hazard ratios for the incidence of SARS-CoV-2 reinfection in studies investigating immune protection among those who had a primary infection with an Omicron subvariant, but different vaccination histories.
CI, confidence interval.
| Epidemiological measure | Cohorts* | |
|---|---|---|
| Two-dose vaccination versus no vaccination before primary Omicron infection | Two-dose cohort | Unvaccinated cohort |
| Incident reinfections (n) | 573 | 1,044 |
| Total follow-up time (person-weeks) | 1,124,759 | 1,121,092 |
| Incidence rate of reinfection (per 10,000 person-weeks; 95% CI) | 5.1 (4.7 to 5.5) | 9.3 (8.8 to 9.9) |
| Unadjusted hazard ratio for SARS-CoV-2 reinfection (95% CI) | 0.55 (0.49 to 0.60) | |
| Adjusted hazard ratio for SARS-CoV-2 reinfection (95% CI)† | 0.59 (0.53 to 0.67) | |
| Hazard ratio for SARS-CoV-2 reinfection additionally adjusted for differences in testing rate (95% CI)† | 0.43 (0.39 to 0.49) | |
| Three-dose vaccination versus two-dose vaccination before primary Omicron infection | Three-dose cohort | Two-dose cohort |
| Incident reinfections (n) | 480 | 248 |
| Total follow-up time (person-weeks) | 585,068 | 586,527 |
| Incidence rate of reinfection (per 10,000 person-weeks; 95% CI) | 8.2 (7.5 to 9.0) | 4.2 (3.7 to 4.8) |
| Unadjusted hazard ratio for SARS-CoV-2 reinfection (95% CI) | 1.94 (1.67 to 2.27) | |
| Adjusted hazard ratio for SARS-CoV-2 reinfection (95% CI)† | 1.96 (1.64 to 2.34) | |
| Hazard ratio for SARS-CoV-2 reinfection additionally adjusted for differences in testing rate (95% CI)† | 1.47 (1.23 to 1.76) | |
| Three-dose vaccination versus no vaccination before primary Omicron infection | Three-dose cohort | Unvaccinated cohort |
| Incident reinfections (n) | 337 | 323 |
| Total follow-up time (person-weeks) | 397,179 | 396,929 |
| Incidence rate of reinfection (per 10,000 person-weeks; 95% CI) | 8.5 (7.6 to 9.4) | 8.1 (7.3 to 9.1) |
| Unadjusted hazard ratio for SARS-CoV-2 reinfection (95% CI) | 1.04 (0.89 to 1.21) | |
| Adjusted hazard ratio for SARS-CoV-2 reinfection (95% CI)† | 1.10 (0.92 to 1.31) | |
| Hazard ratio for SARS-CoV-2 reinfection additionally adjusted for differences in testing rate (95% CI)† | 0.57 (0.48 to 0.68) | |
*Cohorts were matched exactly one-to-one by sex, age, nationality, number of coexisting conditions, as well as the SARS-CoV-2 testing method, the reason for SARS-CoV-2 testing, and the calendar week of the SARS-CoV-2 test of the primary Omicron infection.
†Cox regression analysis adjusted for sex, 10-year age groups, 10 nationality groups, number of coexisting conditions, as well as the SARS-CoV-2 testing method, the reason for SARS-CoV-2 testing, and the calendar week of the SARS-CoV-2 test of the primary Omicron infection.