SARS-CoV-2 Molecular Evolution: A Focus on Omicron Variants in Umbria, Italy.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused more than 6 million deaths worldwide, and the spread of new variants over time increased the ability of this virus to cause infection. The Omicron variant was detected for the first time in Umbria, a region of central Italy, in November 2021 and it induced an unprecedented increase in the number of infection cases. Here, we analysed 3300 SARS-CoV-2 positive samples collected in Umbria between April 2022 and December 2023. We traced the molecular evolution of SARS-CoV-2 variants over time through the Next-Generation Sequencing (NGS) approach. We assessed correlation between SARS-CoV-2 infection and patients' health status. In total, 17.3% of our samples came from patients hospitalised as a consequence of COVID-19 infection even though 81.4% of them received at least three vaccine doses. We identified only Omicron variants, and the BA.5 lineage was detected in the majority of our samples (49.2%). Omicron variants outcompeted each other through the acquisition of mutations especially in Spike glycoprotein that are fingerprints of each variant. Viral antigenic evolution confers higher immunological escape and makes a continuous improvement of vaccine formulation necessary. The continuous update of international genomic databases with sequencing results obtained by emergent pathogens is essential to manage a possible future pandemic.