Comparison of the Risk of Hospitalization and Severe Disease Among Co-circulating Severe Acute Respiratory Syndrome Coronavirus 2 Variants

We compare the risk of coronavirus disease 2019 (COVID-19) outcomes among co-circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants between January 2021 and May 2022 in Navarra, Spain. We compared the frequency of hospitalization and severe disease (intensive care unit admission or death) due to COVID-19 among the co-circulating variants. Variants analyzed were nonvariants of concern (non-VOCs), Alpha, Delta, Omicron BA.1, and Omicron BA.2. Logistic regression models were used to estimate adjusted odds ratio (aOR). The Alpha variant had a higher risk of hospitalization (aOR, 1.86 [95 confidence interval {CI}, 1.282.71]) and severe disease (aOR, 2.40 [95 CI, 1.314.40]) than non-VOCs. The Delta variant did not show a significantly different risk of hospitalization (aOR, 0.73 [95 CI, .401.30]) and severe disease (aOR, 3.04 [95 CI, .5716.22]) compared to the Alpha variant. The Omicron BA.1 significantly reduced both risks relative to the Delta variant (aORs, 0.28 [95 CI, .16.47] and 0.23 [95 CI, .12.46], respectively). The Omicron BA.2 reduced the risk of hospitalization compared to BA.1 (aOR, 0.52 [95 CI, .29.95]). The Alpha and Delta variants showed an increased risk of hospitalization and severe disease, which decreased considerably with the Omicron BA.1 and BA.2. Surveillance of variants can lead to important differences in severity.