Comparison of the risk of hospitalisation and severe disease among co-circulating SARS-CoV-2 variants

Abstract Background We aimed to compare the risk of COVID-19 outcomes among co-circulating SARS-CoV-2 variants between January 2021 and May 2022 in Navarra, Spain. Methods We compared the frequency of hospitalisation and severe disease (intensive care unit admission or death) due to COVID-19 between cases of each dominant variant and the next one over weeks with co-circulation. Variants analysed were non-variants of concern (non-VOCs), Alpha, Delta, Omicron BA.1, and Omicron BA.2. Logistic regression models were used to estimate adjusted odds ratio (aOR). Results The Alpha variant had a higher risk of hospitalisation (aOR = 1.86; 95%CI:1.28-2.71) and severe disease (aOR = 2.40; 95%CI:1.31-4.40) than non-VOCs. The Delta variant did not show a significantly different risk of hospitalisation (aOR = 0.73; 95%CI:0.40-1.30) and severe disease (aOR = 3.04; 95%CI:0.57-16.22) compared to the Alpha variant. The Omicron BA.1 subvariant significantly reduced both risks relative to the Delta variant (aOR = 0.28; 95%CI:0.16-0.47; aOR = 0.23; 95%CI:0.12-0.46, respectively). The Omicron BA.2 subvariant reduced the risk of hospitalisation compared to the BA.1 (aOR = 0.52; 95%CI:0.29-0.95). Conclusions The Alpha and Delta variants were associated with an increased risk of hospitalisation and severe disease, which decreased considerably with the Omicron BA.1 and BA.2 subvariants. Surveillance of variants is essential since they can lead important differences in severity.