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ObjectivesThe emergence of SARS-CoV-2 variants raised questions over the extent to which vaccines designed in 2020 have remained effective. We aimed to assess whether vaccine status was associated with the severity of Omicron SARS-CoV-2 infection in hospitalised patients. MethodsWe conducted an international, multicentric, retrospective study in 14 centres (Bulgaria, Croatia, France, Turkey). We collected data on patients hospitalised [≥]24 hours between 01/12/2021 and 03/03/2022, with PCR-confirmed infection at a time of exclusive Omicron circulation, with hospitalisation related or not to the infection. Patients who had received prophylaxis by monoclonal antibodies were excluded. Patients were considered fully vaccinated if they had received at least 2 injections of either mRNA and/or ChAdOx1-S, or 1 injection of Ad26.CoV2-S vaccines. ResultsAmong the 1215 patients (median [IQR] age 73.0 [57.0; 84.0]; 51.3% males), 746 (61.4%) were fully vaccinated. In multivariate analysis, being vaccinated was associated with lower 28-day mortality (RR=0.50 [0.32-0.77]), ICU admission (R=0.40 [0.26-0.62], and oxygen requirement (RR=0.34 [0.25-0.46]), independently of age and comorbidities. When co-analysing these Omicron patients with 948 Delta patients from a study we recently conducted, Omicron infection was associated with lower 28-day mortality (RR=0.53 [0.37-0.76]), ICU admission (R=0.19 [0.12-0.28], and oxygen requirements (RR=0.50 [0.38-0.67]), independently of age, comorbidities and vaccination status. ConclusionsmRNA- and adenovirus-based vaccines have remained effective on severity of Omicron SARS-CoV-2 infection. Omicron is associated with a lower risk of severe forms, independently of vaccination and patient characteristics.
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BackgroundMost respiratory viruses show pronounced seasonality, but for SARS-CoV-2 this still needs to be documented. MethodsWe examined the disease progression of COVID-19 in 6,914 patients admitted to hospitals in Europe and China. In addition, we evaluated progress of disease symptoms in 37,187 individuals reporting symptoms into the COVID Symptom Study application. FindingsMeta-analysis of the mortality risk in eight European hospitals estimated odds ratios per one day increase in the admission date to be 0.981 (0.973-0.988, p<0.001) and per increase in ambient temperature of one degree Celsius to be 0.854 (0.773-0.944, p=0.007). Statistically significant decreases of comparable magnitude in median hospital stay, probability of transfer to Intensive Care Unit and need for mechanical ventilation were also observed in most, but not all hospitals. The analysis of individually reported symptoms of 37,187 individuals in the UK also showed the decrease in symptom duration and disease severity with time. InterpretationSeverity of COVID-19 in Europe decreased significantly between March and May and the seasonality of COVID-19 is the most likely explanation. Mucosal barrier and mucociliary clearance can significantly decrease viral load and disease progression, and their inactivation by low relative humidity of indoor air might significantly contribute to severity of the disease.