Table 4.
Characteristics of SARS-CoV-2 reinfections during the Omicron wave, using a 60-days interval between cases
| Previously infected individuals at the start of the Omicron wave n (%) | Reinfections n(%) | Hazard ratio | Adjusted Hazard ratio* | Adjusted P-value* | |
|---|---|---|---|---|---|
| Sex | |||||
| Male | 131903 (51.1) | 7367 (5.6) | Ref. | Ref. | - |
| Female | 126204 (48.9) | 7784 (6.2) | 1.11 (1.08-1.15) | 1.15 (1.11-1.18) | <0.001 |
| Age (in years) | |||||
| 0-11 | 40110 (15.5) | 2972 (7.4) | 1.46 (1.39-1.54) | 1.08 (1.01-1.15) | 0.017 |
| 12-17 | 39250 (15.2) | 4080 (10.4) | 1.92 (1.84-2.02) | 1.67 (1.58-1.76) | <0.001 |
| 18-29 | 52590 (20.4) | 3480 (6.6) | 1.17 (1.11-1.22) | 1.15 (1.10-1.21) | <0.001 |
| 30-44 | 56581 (21.9) | 3059 (5.4) | Ref. | Ref. | - |
| 45-54 | 32985 (12.8) | 1117 (3.4) | 0.62 (0.58-0.66) | 0.72 (0.67-0.77) | <0.001 |
| 55-64 | 19229 (7.5) | 340 (1.8) | 0.32 (0.29-0.36) | 0.40 (0.36-0.45) | <0.001 |
| 65-74 | 9799 (3.8) | 70 (0.7) | 0.13 (0.11-0.17) | 0.20 (0.16-0.25) | <0.001 |
| >=75 | 7563 (2.9) | 33 (0.4) | 0.08 (0.05-0.11) | 0.11 (0.08-0.16) | <0.001 |
| County | |||||
| Agder | 10035 (3.9) | 508 (5.1) | Ref. | - | - |
| Innlandet | 10805 (4.2) | 413 (3.8) | 0.73 (0.64-0.84) | ||
| Møre og Romsdal | 5789 (2.2) | 114 (2.0) | 0.39 (0.32-0.48) | ||
| Nordland | 5287 (2.0) | 112 (2.1) | 0.42 (0.34-0.51) | ||
| Oslo | 67501 (26.1) | 5543 (8.2) | 1.62 (1.48-1.77) | ||
| Rogaland | 14441 (5.6) | 483 (3.3) | 0.66 (0.58-0.74) | ||
| Troms og Finnmark | 9278 (3.6) | 148 (1.6) | 0.32 (0.26-0.38) | ||
| Trøndelag | 16329 (6.3) | 669 (4.1) | 0.81 (0.73-0.91) | ||
| Vestfold og Telemark | 15347 (6.0) | 763 (5.0) | 1.00 (0.89-1.12) | ||
| Vestland | 21439 (8.3) | 840 (3.9) | 0.79 (0.71-0.88) | ||
| Viken | 81856 (31.7) | 5558 (6.8) | 1.34 (1.23-1.47) | ||
| Country of birth | |||||
| Foreign | 74037 (28.7) | 4563 (6.2) | Ref. | - | - |
| Norway | 179856 (69.7) | 10568 (5.9) | 0.99 (0.95-1.02) | ||
| Unknown | 4214 (1.6) | 20 (0.5) | 0.08 (0.05-0.12) | ||
| Risk group | |||||
| No comorbidity | 224701 (87.1) | 13796 (6.1) | Ref. | Ref. | - |
| Medium risk comorbidity | 30137 (11.7) | 1286 (4.3) | 0.69 (0.65-0.73) | 1.10 (1.03-1.16) | 0.002 |
| High risk comorbidity | 3269 (1.3) | 69 (2.1) | 0.34 (0.27-0.43) | 0.78 (0.62-0.99) | 0.041 |
| Vaccine status | |||||
| Unvaccinated | 93857 (36.4) | 7971 (8.5) | Ref. | Ref. | - |
| Vaccinated with one dose <21 days earlier | 2635 (1.0) | 98 (3.7) | 0.42 (0.34-0.51) | 0.38 (0.31-0.46) | <0.001 |
| Vaccinated with one dose >=21 days earlier | 58983 (22.9) | 4778 (8.1) | 0.78 (0.75-0.81) | 0.72 (0.69-0.75) | <0.001 |
| Maximum of two doses 7-179 days prior | 69593 (27.0) | 1880 (2.7) | 0.33 (0.31-0.35) | 0.40 (0.38-0.42) | <0.001 |
| Maximum of two doses ≥180 days prior | 24572 (9.5) | 292 (1.2) | 0.16 (0.14-0.18) | 0.37 (0.32-0.41) | <0.001 |
| Three doses | 8467 (3.3) | 132 (1.6) | 0.21 (0.17-0.25) | 0.40 (0.33-0.48) | <0.001 |
| Most recent infection prior to Omicron wave | |||||
| Pre-alpha infection | 42558 (16.5) | 3012 (7.1) | Ref. | Ref. | - |
| Inter-wave pre-alpha/Alpha | 30757 (11.9) | 2423 (7.9) | 1.12 (1.06-1.18) | 0.93 (0.88-0.98) | 0.006 |
| Alpha wave infection | 42321 (16.4) | 3406 (8.1) | 1.14 (1.09-1.20) | 0.87 (0.83-0.91) | <0.001 |
| Inter-wave Alpha/Delta | 10425 (4.0) | 693 (6.7) | 0.93 (0.86-1.02) | 0.83 (0.76-0.90) | <0.001 |
| Delta wave infection | 132046 (51.2) | 5617 (4.3) | 0.77 (0.74-0.81) | 0.56 (0.54-0.59) | <0.001 |
Characteristics of SARS-CoV-2 reinfection cases during the Omicron wave, using a 60-days interval between cases. Hazard ratio estimates for reinfection using stratified Cox regression model in Norway 26 February 2020 - 31 January 2022 (n = 258 107)
*Sex, age group, risk group, vaccine status, the most recent infection prior to the Omicron wave was included in a multivariate model, stratifying for county of residence and country of birth