Disease severity related to VOC dominance in unvaccinated SARS-CoV-2 positive adults without risk factors in Sweden
Although the emerging SARS-CoV-2 variants of concern (VOC) have shown increasing transmissibility, their role for causing severe disease has not been fully clarified. Here, we studied changes in rates of hospitalisation and severe illness (subjection to high-flow nasal oxygen or admission to an intensive care unit during hospital stay) among all (n=685 891) unvaccinated SARS-CoV-2 positive adults without risk factors in Sweden from November 2020 to September 2021. After adjustment for age, sex, and socio-economic factors, and with November 2020 (non-VOC period) as reference, the odds ratios (OR) for hospitalisation were 1.6-1.7 in March-May 2021 (Alpha VOC dominance) and 2.4-3.0 in June-September 2021 (Delta VOC dominance), and the ORs for severe illness were 1.8-2.1 in March-May 2021 and 3.1-4.7 in June-September 2021. This study shows that unvaccinated adults without risk factors, have had a gradually increased risk for hospital admission and severe illness when infected with the Alpha and Delta VOCs, respectively.