Real-life Evidence of Lower Lung Virulence in COVID-19 Inpatients Infected with SARS-CoV-2 Omicron Variant Compared to Wild-Type and Delta SARS-CoV-2 Pneumonia.

In vitro and animal models described lower replication capacity and virulence of SARS-CoV-2 Omicron lineage in lower respiratory airways compared to wild type and other variants of concern (oVOCs). Among adult subjects admitted to our hospital (Turin, Italy) due to wild type, oVOCs, and Omicron SARS-CoV-2-related pneumonia (n = 100 for each lineage), the cases of Omicron pneumonia showed lower degree of lung parenchyma involvement (aß -1.471, p = 0.037), less tendency to parenchyma consolidation (aOR 0.500, p = 0.011), and better respiratory functions (assessed by ambient air arterial blood gas analysis). After adjusting for demographic, previous immunity, and comorbidities, Omicron pneumonia still associated with lower risk of respiratory failure (for severe respiratory failure, Wild-type versus Omicron aOR 15.6, p = 0.005 and oVOCs versus Omicron aOR 31.7, p < 0.001). These observations are in line with preliminary findings from in vitro and animal models and could explain why Omicron infection has been associated with lower mortality and hospitalization in human.

Determinants of SARS-CoV-2 Contagiousness in Household Contacts of Symptomatic Adult Index Cases.

Background: Identifying determinants of the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) transmission in settings of contagion is fundamental to inform containment strategies. We assessed SARS-CoV-2 cycle threshold value (Ct) from the first diagnostic nasal-pharyngeal swab of symptomatic index cases and which demographic or clinical characteristics among cases and contacts are associated with transmission risk within households. Methods: This is a retrospective prevalence study on secondary SARS-CoV-2 cases (SC) among the household contacts of symptomatic adult index cases randomly sampled from all the SARS-CoV-2-positive diagnostic nasopharyngeal swabs analyzed at our regional referral hospital (Amedeo di Savoia Hospital, Turin, Italy) in March, 2020. Index cases underwent a telephone survey to collect their demographic and clinical data and all their household contacts. The Ct value of RdRp gene from the first diagnostic swab of index cases was recorded and index cases were grouped according to Ct tertiles (A < first tertile, first ≤ B ≤ second tertile, C ≥ second tertile). Post hoc analysis was performed in SC as well as contacts that did not undergo SARS-CoV-2 testing but developed compatible signs and symptoms. Non-parametric tests and generalized linear models were run. Results: Index (n = 72) and contact (n = 164) median age was 54 (48-63) and 32 (20-56) years, respectively. A total of 60, 50, and 54 subjects were contacts of group A, B, and C index cases, respectively; 35.9% of contacts were SC. Twenty-four further subjects (14.6%) met the criteria for symptom-based likely positive SC. The secondary attack rate was 36.0% (28.6-43.4), assuming a mean incubation period of 5 days and a maximum infectious period of 20 days. SC prevalence differed between Ct groups (53.3% A, 32.0% B, 20.4% C; p < 0.001). No difference in SC was found according to sex, presence of signs/symptoms, and COVID-19 severity of index cases, or according to contacts' sex and number per household. The age of both index cases [aOR 4.52 (1.2-17.0) for 60 vs. ≤45 years old] and contacts [aOR 3.66 (1.3-10.6) for 60 vs. ≤45years old] and the Ct of the index [aOR 0.17 (0.07-0.4) for Ct ≥ 31.8 vs. Ct < 24.4] independently associated with SC risk. Sensitivity analysis including symptoms-based likely positive SC supported all the previous results. Conclusion: In confined transmission settings such as households, PCR Ct values may inform on the contagiousness of infected subjects and age may modulate transmission/contagion risk.

Risk for SARS-CoV-2 Infection in Healthcare Workers, Turin, Italy.

We measured severe acute respiratory syndrome coronavirus 2 spike protein subunits S1/S2 antibodies by using capillary electrophoresis and a chemiluminescence immunoassay for 5,444 active healthcare workers in Italy. Seroprevalence was 6.9% and higher among participants having contact with patients. Seroconversion was not observed in 37/213 previously infected participants.