Table 5.
Characteristics of SARS-CoV-2 reinfections during the Delta wave, using a 60-day interval between cases
| Previously infected individuals at the start of the Delta wave n (%) | Reinfections n(%) | Hazard ratio | Adjusted Hazard ratio* | Adjusted P-value* | |
|---|---|---|---|---|---|
| Sex | |||||
| Male | 67840 (52.2) | 423 (0.6) | Ref. | Ref. | - |
| Female | 62208 (47.8) | 386 (0.6) | 0.99 (0.86-1.14) | 1.00 (0.87-1.15) | 0.998 |
| Age (in years) | |||||
| 0-11 | 13650 (10.5) | 94 (0.7) | 0.99 (0.78-1.27) | 0.50 (0.38-0.65) | <0.001 |
| 12-17 | 12093 (9.3) | 152 (1.3) | 1.85 (1.50-2.28) | 1.11 (0.88-1.40) | 0.374 |
| 18-29 | 34549 (26.6) | 235 (0.7) | 1.03 (0.86-1.25) | 1.06 (0.87-1.28) | 0.567 |
| 30-44 | 30755 (23.6) | 209 (0.7) | Ref. | Ref. | - |
| 45-54 | 18633 (14.3) | 71 (0.4) | 0.56 (0.42-0.73) | 0.65 (0.50-0.86) | 0.002 |
| 55-64 | 11534 (8.9) | 27 (0.2) | 0.34 (0.23-0.51) | 0.40 (0.27-0.61) | <0.001 |
| 65-74 | 5005 (3.9) | 11 (0.2) | 0.32 (0.17-0.58) | 0.36 (0.19-0.67) | 0.001 |
| >=75 | 3829 (2.9) | 10 (0.3) | 0.38 (0.20-0.71) | 0.26 (0.13-0.51) | <0.001 |
| County | |||||
| Agder | 5425 (4.2) | 18 (0.3) | Ref. | - | - |
| Innlandet | 5913 (4.5) | 23 (0.4) | 1.12 (0.61-2.08) | ||
| Møre og Romsdal | 2017 (1.6) | 3 (0.1) | 0.46 (0.14-1.58) | ||
| Nordland | 1648 (1.3) | 3 (0.2) | 0.55 (0.16-1.88) | ||
| Oslo | 36645 (28.2) | 343 (0.9) | 2.67 (1.66-4.29) | ||
| Rogaland | 7493 (5.8) | 35 (0.5) | 1.42 (0.80-2.51) | ||
| Troms og Finnmark | 2424 (1.9) | 14 (0.6) | 1.81 (0.90-3.65) | ||
| Trøndelag | 5411 (4.2) | 25 (0.5) | 1.38 (0.75-2.53) | ||
| Vestfold og Telemark | 8867 (6.8) | 36 (0.4) | 1.18 (0.67-2.07) | ||
| Vestland | 10069 (7.7) | 56 (0.6) | 1.65 (0.97-2.81) | ||
| Viken | 44136 (33.9) | 253 (0.6) | 1.64 (1.02-2.65) | ||
| Country of birth | |||||
| Foreign | 42958 (33.0) | 284 (0.7) | Ref. | - | - |
| Norway | 84979 (65.3) | 522 (0.6) | 0.94 (0.81-1.09) | ||
| Unknown | 2111 (1.6) | 3 (0.1) | 0.21 (0.07-0.66) | ||
| Risk group | |||||
| No comorbidity | 112273 (86.3) | 715 (0.6) | Ref. | Ref. | . |
| Medium risk comorbidity | 16071 (12.4) | 83 (0.5) | 0.80 (0.63-1.00) | 1.19 (0.94-1.51) | 0.143 |
| High risk comorbidity | 1704 (1.3) | 11 (0.7) | 0.99 (0.55-1.79) | 1.70 (0.92-3.12) | 0.088 |
| Vaccine status | |||||
| Unvaccinated | 38068 (29.3) | 464 (1.2) | Ref. | Ref. | - |
| Vaccinated with one dose <21 days earlier | 1889 (1.4) | 31 (1.6) | 0.86 (0.60-1.25) | 0.83 (0.57-1.21) | 0.329 |
| Vaccinated with one dose >=21 days earlier | 73536 (56.5) | 262 (0.4) | 0.33 (0.28-0.38) | 0.29 (0.24-0.35) | <0.001 |
| Maximum of two doses 7-179 days prior | 12062 (9.3) | 29 (0.2) | 0.34 (0.23-0.50) | 0.35 (0.24-0.52) | <0.001 |
| Maximum of two doses ≥180 days prior | 2936 (2.3) | 20 (0.7) | 0.76 (0.48-1.18) | 0.85 (0.53-1.37) | 0.514 |
| Three doses | 1557 (1.2) | 3 (0.2) | 0.41 (0.13-1.27) | 0.64 (0.20-2.08) | 0.459 |
| Most recent infection prior to Delta wave | |||||
| Pre-alpha infection | 44003 (33.8) | 311 (0.7) | Ref. | Ref. | - |
| Inter-wave pre-alpha/Alpha | 31797 (24.4) | 212 (0.7) | 0.94 (0.79-1.12) | 0.85 (0.71-1.01) | 0.070 |
| Alpha wave infection | 43551 (33.5) | 231 (0.5) | 0.75 (0.63-0.89) | 0.58 (0.49-0.70) | <0.001 |
| Inter-wave Alpha/Delta | 10697 (8.2) | 55 (0.5) | 1.45 (1.08-1.94) | 1.04 (0.77-1.41) | 0.793 |
Characteristics of SARS-CoV-2 reinfection cases during the Delta wave, using a 60-day interval between cases. Hazard ratio estimates for reinfection using stratified Cox regression model in Norway 26 February - 31 January 2022. (n = 130 048)
*Sex, age group, risk group, vaccine status, the most recent infection prior to the Delta wave was included in a multivariate model, stratifying for county of residence and country of birth