Table 2 Effectiveness against reinfection in the BA.1-against-BA.2 and BA.2-against-BA.1 studies

From: Protection of Omicron sub-lineage infection against reinfection with another Omicron sub-lineage

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)

  1. CI confidence interval.
  2. *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.
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