Since early 2022 the Omicron variant has rapidly spread worldwide, becoming the dominant variant to date. The study aimed to investigate the clinical and epidemiological characteristics of COVID-19 patients and to reconstruct the genomic epidemiology of main SARS-CoV-2 Omicron sub-lineages in Italy in 2022. 8,970 SARS-CoV-2 samples were studied, and phylogenetic analyses were focused on BA.1, BA.2 and BA.5 sub-variants. More than half of subjects received three doses of vaccine and experienced a reinfection. A significant larger proportion of unvaccinated subjects presented reinfection compared to vaccinated. Clusters presented a tMRCA between September-November 2021 (BA.1), November 2021-January 2022 (BA.2) and October 2021-May 2022 (BA.5). R e values showed the highest level between September-October, January-February 2022, and May 2022 for BA.1, BA.2 and BA.5, respectively. Limited number of studied variant sequences are included in clusters. The analyses dissect the epidemiological dynamics of Omicron sub-lineages in Italy over a period of great epidemiological changes in the COVID-19 epidemic. The spread rate of the studied variant exceeded its evolutionary rate. No single sub-lineage had sufficient time to differentiate into large clusters, but only into small and fragmented groups sharing the same recent ancestor. These analyses dissect the epidemiological dynamics of Omicron sub-lineages in Italy over a period of great epidemiological changes in the COVID-19 epidemic.

Introduction: Human respiratory syncytial virus (RSV) is one of the most frequent causes of respiratory infections in children under five years of age, but its socio-economic impact and burden in primary care settings is still little studied. Methods: During the 2022/23 winter season, 55 pediatricians from five Italian regions participated in our community-based study. They collected a nasal swab for RSV molecular test from 650 patients under the age of 5 with Acute Respiratory Infections (ARIs) and performed a baseline questionnaire. The clinical and socio-economic burden of RSV disease in primary care was evaluated by two follow-up questionnaires completed by the parents of positive children, on day 14 and 30. Results: RSV laboratory-confirmed cases were 37.8% of the total recruited ARI cases, with RSV subtype B accounting for the majority (65.4%) of RSV-positive swabs. RSV-positive children were younger than RSV-negative ones (median 12.5 vs 16.5 months). The mean duration of symptoms for all children infected by RSV was 11.47 ± 6.27 days. We did not observe substantial differences in clinical severity between the two RSV subtypes, but RSV-A positive patients required more additional pediatric examinations than RSV-B cases. The socioeconomic impact of RSV infection was considerable, causing 53% of children to be absent from school, 46% of parents to lose working days and 25% of families to incur extra costs. Conclusions: Our findings describe a baseline of the RSV disease burden in primary care in Italy before the introduction of upcoming immunization strategies.