Table 2.
Effectiveness against reinfection in the BA.1-against-BA.2 and BA.2-against-BA.1 studies
| Epidemiological measure | BA.1-against-BA.2 study | BA.2-against-BA.1 study | ||
|---|---|---|---|---|
| Effectiveness of BA.1 infection against reinfection with BA.2 | Effectiveness of BA.2 infection against reinfection with BA.1 | |||
| Estimate (95% CI) | Effectiveness in % (95% CI) | Estimate (95% CI) | Effectiveness in % (95% CI) | |
| Total follow-up time—BA.1/BA.2-infected cohort (person-weeks) | 122,626 | — | 598,438 | — |
| Total follow-up time—Uninfected-control cohort (person-weeks) | 121,572 | — | 595,257 | — |
| Incidence rate of infection— BA.1/BA.2-infected cohort (per 10,000 person-weeks) | 1.1 (0.6 to 2.0) | — | 0.9 (0.6 to 1.2) | — |
| Incidence rate of infection—Uninfected-control cohort (per 10,000 person-weeks) | 16.9 (14.6 to 19.7) | — | 4.3 (3.7 to 5.1) | — |
| Unadjusted hazard ratio for infection | 0.06 (0.03 to 0.12) | 93.6 (88.2 to 96.6) | 0.20 (0.15 to 0.29) | 79.6 (71.3 to 85.5) |
| Adjusted hazard ratio for infection* | 0.06 (0.03 to 0.11) | 94.2 (89.2 to 96.9) | 0.19 (0.14 to 0.27) | 80.9 (73.1 to 86.4) |
CI confidence interval.
*Cox regression analysis adjusted for sex, 10-year age group (Table 1), ten nationality groups (Table 1), comorbidity count (Table 1), and vaccination status. In the BA.1-against-BA.2 study, the adjusted hazard ratio relative to unvaccinated was 1.41 (95% CI: 0.64 to 3.10) for one vaccine dose, 1.92 (95% CI: 1.08 to 3.43) for two vaccine doses, and 1.07 (95% CI: 0.59 to 1.94) for three or more vaccine doses. In the BA.2-against-BA.1 study, the adjusted hazard ratio relative to unvaccinated was 1.74 (95% CI: 0.60 to 5.00) for one vaccine dose, 1.84 (95% CI: 1.19 to 2.87) for two vaccine doses, and 1.31 (95% CI: 0.85 to 2.01) for three or more vaccine doses.