Table 3.
Association between hospitalization and infection with the Delta variant compared with the Alpha variant of severe acute respiratory syndrome coronavirus-2 (multi-variable binomial regression adjusted for demographic characteristics and underlying comorbidities), overall and stratified (subgroup analysis) by sex, age group, country of birth, underlying comorbidities and vaccination status at date of positive test, Norway, 3 May–15 August 2021.
| Hospitalization | ||||
|---|---|---|---|---|
| Alpha cases (n=12,078) | Delta cases (n=7,977) | Delta vs Alpha, adjusted risk ratio (95% CI) | ||
| Overall | 240 (2.0 %) | 107 (1.3 %) | 0.97 (0.76–1.23) | |
| Subgroup analysis by: | ||||
| Sex | Female | 104 (1.8%) | 53 (1.4%) | 1.12 (0.79–1.58) |
| Male | 136 (2.2%) | 54 (1.3%) | 0.85 (0.61–1.17) | |
| Age group (years) | 0–24 | 11 (0.2%) | 13 (0.4%) | 1.96 (0.83–4.64) |
| 25-44 | 69 (2.0%) | 44 (1.5%) | 1.00 (0.68–1.48) | |
| 45–64 | 120 (6.0%) | 35 (3.3%) | 1.10 (0.74–1.65) | |
| >65 | 40 (15%) | 15 (7.9%) | 0.60 (0.34–1.05) | |
| Country of birth (Norwegian born) | Yes | 131 (1.5%) | 49 (0.9%) | 1.01 (0.72–1.41) |
| No | 101 (3.1%) | 55 (2.2%) | 1.03 (0.74–1.43) | |
| Unknown | 8 (8.5%) | 3 (5.7%) | 1.49 (0.40–5.49) | |
| Risk for severe COVID-19a | No underlying comorbidities | 173 (1.6%) | 86 (1.2%) | 1.06 (0.81–1.39) |
| Medium-risk comorbidity | 57 (5.5%) | 16 (2.7%) | 0.61 (0.35–1.09) | |
| High-risk comorbidity | 10 (13%) | 5 (9.8%) | 1.51 (0.69–3.29) | |
| Vaccination status at date of positive test | Not vaccinated | 184 (1.7%) | 73 (1.6%) | 1.10 (0.84–1.45) |
| Vaccinated with one dose <21 days before positive test | 35 (4.8%) | 7 (0.7%) | 0.43 (0.17–1.11) | |
| Partially vaccinated | 12 (2.6%) | 14 (0.7%) | 1.45 (0.51–4.15) | |
| Fully vaccinated | 9 (5.1%) | 13 (2.1%) | 0.70 (0.29–1.67) | |
COVID-19, coronavirus disease 2019; CI, confidence interval.
Week of sampling and county of residence were not significant predictors in the multi-variable model, and not included in the final model.
Risk for severe disease based on underlying comorbidities that are associated with moderate or high risk of serious illness regardless of age. Details on the definitions of medium- and high-risk categories are provided in Section 1 of the online supplementary material.