Table 2.
Effectiveness of previous pre-Omicron infection, vaccination with BNT162b2, and hybrid immunity of previous infection and vaccination against symptomatic Alpha, Beta, or Delta infections and against severe, critical, or fatal COVID-19 due to infection with these variants.
| Analyses | Cases (PCR-positive)a |
Controls (PCR-negative)a |
Effectiveness against symptomatic infection (95% CI) | Cases (Severe, critical, or fatal COVID-19)b |
Controls (PCR- negative)b |
Effectiveness against severe, critical, or fatal COVID-19 (95% CI) | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| Exposed | Unexposedc | Exposed | Unexposedc | Exposed | Unexposedc | Exposed | Unexposedc | |||
| Alpha symptomatic infectiond | ||||||||||
| Previous infection and no vaccination | 41 | 7122 | 686 | 12,855 | 89.5 (85.5–92.3) | 0 | 438 | 99 | 1641 | 100.0 (96.2–100.0)e |
| Two doses and no previous infection | 15 | 7122 | 255 | 12,855 | 90.5 (83.9–94.4) | 1 | 438 | 74 | 1641 | 96.1 (71.2–99.5) |
| Two doses and previous infection | 0 | 7122 | 25 | 12,855 | 100.0 (84.1–100.0)e | 0 | 438 | 3 | 1641 | 100.0 (−58.7 to 100.0)e |
| Three doses and no previous infection | 0 | 7122 | 0 | 12,855 | – | 0 | 438 | 0 | 1641 | – |
| Three doses and previous infection | 0 | 7122 | 0 | 12,855 | – | 0 | 438 | 0 | 1641 | – |
| Beta symptomatic infectiond | ||||||||||
| Previous infection and no vaccination | 132 | 17,738 | 1631 | 28,012 | 87.9 (85.4–89.9) | 1 | 1420 | 291 | 4028 | 99.0 (92.8–99.9) |
| Two doses and no previous infection | 1135 | 17,738 | 6376 | 28,012 | 80.5 (79.0–82.0) | 25 | 1420 | 1443 | 4028 | 97.4 (95.8–98.4) |
| Two doses and previous infection | 13 | 17,738 | 516 | 28,012 | 97.4 (95.4–98.5) | 0 | 1420 | 125 | 4028 | 100.0 (97.0–100.0)e |
| Three doses and no previous infection | 1 | 17,738 | 7 | 28,012 | 84.7 (−22.7 to 98.2) | 0 | 1420 | 1 | 4028 | 100.0 (−97.4 to 100.0)e |
| Three doses and previous infection | 0 | 17,738 | 2 | 28,012 | 100.0 (−81.2 to 100.0)e | 0 | 1420 | 0 | 4028 | – |
| Delta symptomatic infectiond | ||||||||||
| Previous infection and no vaccination | 52 | 4207 | 654 | 5844 | 90.0 (86.7–92.5) | 0 | 189 | 36 | 244 | 100.0 (89.2–100.0)e |
| Two doses and no previous infection | 2856 | 4207 | 6236 | 5844 | 58.1 (54.6–61.3) | 59 | 189 | 544 | 244 | 91.1 (86.3–94.2) |
| Two doses and previous infection | 59 | 4207 | 965 | 5844 | 94.5 (92.8–95.8) | 0 | 189 | 85 | 244 | 100.0 (95.6–100.0)e |
| Three doses and no previous infection | 26 | 4207 | 219 | 5844 | 91.7 (87.1–94.7) | 0 | 189 | 21 | 244 | 100.0 (80.8–100.0)e |
| Three doses and previous infection | 1 | 4207 | 36 | 5844 | 98.1 (85.7–99.7) | 0 | 189 | 3 | 244 | 100.0 (−58.7 to 100.0)e |
CI denotes confidence interval, COVID-19 coronavirus disease 2019, and PCR polymerase chain reaction.
Cases and controls were exactly matched one-to-two by sex, 10-year age group, nationality, number of coexisting conditions, and calendar week of PCR test.
Cases and controls were exactly matched one-to-five by sex, 10-year age group, nationality, number of coexisting conditions, and calendar week of PCR test.
Unexposed was defined as no previous infection and no vaccination.
A symptomatic infection was defined as a PCR-positive nasopharyngeal swab that was obtained because of the presence of symptoms consistent with a respiratory tract infection. Effectiveness was estimated with the use of a test-negative, case-control study design. COVID-19 severity, criticality, and fatality were defined according to World Health Organization guidelines.
The 95% confidence interval was estimated with the use of McNemar’s test because of zero events among exposed cases. Since n:1 matching was employed, the number of pairs was considered as ‘n’. This approach provided only an approximate estimate for the 95% CI in these specific situations.