Table 2.
Effectiveness of Booster Vaccination with mRNA Vaccine Against SARS-CoV-2 Infection and COVID-19 Caused by the Omicron Variant Among Participants in the Norwegian Mother, Father, and Child Cohort Study and the Senior Cohort, N = 85 801
| SARS-CoV-2 Infection | Mild COVID-19 | Moderate COVID-19 | Severe COVID-19 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Interval From Vaccination, d | Person-Time, d | Cases, na | rVEb (95% CI) | Cases, n | rVEb (95% CI) | Cases, n | rVEb (95% CI) | Cases, n | rVEb (95% CI) |
| 2 dosesc | |||||||||
| >130 | 419 536 | 4895 | Ref | 1607 | Ref | 2858 | Ref | 307 | Ref |
| Booster vaccinationd | |||||||||
| 0–6 | 115 285 | 864 | 32.4 (27.2–37.2) | 412 | 0.9 (−10.8 to 11.3) | 396 | 45.6 (39.5–51.2) | 28 | 61.9 (43.5–74.3) |
| 7–30 | 864 567 | 8506 | 41.4 (39.2–43.5) | 4177 | 7.9 (2.1–13.4) | 3819 | 56.0 (53.7–58.1) | 179 | 80.9 (76.9–84.2) |
| 31–60 | 1 168 176 | 16 324 | 37.1 (34.9–39.2) | 7506 | 7.9 (2.3–13.1) | 7912 | 49.2 (46.8–51.4) | 408 | 76.4 (72.4–79.8) |
| 61–90 | 677 064 | 8877 | 32.8 (30.2–35.4) | 3875 | 8.5 (2.4–14.2) | 4512 | 42.6 (39.5–45.5) | 264 | 69.2 (63.1–74.3) |
| 91–120 | 171 546 | 1826 | 25.5 (20.9–29.8) | 859 | −4.4 (−14.5 to 4.9) | 864 | 38.2 (32.9–43.2) | 61 | 63.4 (50.5–72.9)e |
| >120 | 13 763 | 170 | 12.2 (−2.6 to 24.8) | 83 | −25.6 (−57.3 to −.3) | 79 | 27.1 (8.6–41.8) | …e | …e |
Abbreviations: CI, confidence interval; COVID-19, coronavirus disease 2019; HR, hazard ratio; Ref, reference; rVE, relative vaccine effectiveness; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
Includes asymptomatic SARS-CoV-2 infections and SARS-CoV-2 infection not possible to classify according to severity. Thus, the number of cases exceeds the sum of mild, moderate, and severe COVID-19 cases.
rVE = 100% × (1 − HR). HR was estimated using a stratified Cox model with county as strata and calendar time as the underlying time scale. The model was adjusted for previous SARS-CoV-2 infection, age, and sex.
The reference category consisted of person-time more than 130 days after the second vaccine dose up until booster vaccination.
Booster vaccination was defined as a third vaccine dose received at least 130 days after the second dose.
For severe COVID-19, the upper category was receipt of booster vaccination more than 90 days previously.