TY - JOUR AU - Kifer, Domagoj AU - Bugada, Dario AU - Villar-Garcia, Judit AU - Gudelj, Ivan AU - Menni, Cristina AU - Sudre, Carole AU - Vučković, Frano AU - Ugrina, Ivo AU - Lorini, Luca F. AU - Posso, Margarita AU - Bettinelli, Silvia AU - Ughi, Nicola AU - Maloberti, Alessandro AU - Epis, Oscar AU - Giannattasio, Cristina AU - Rossetti, Claudio AU - Kalogjera, Livije AU - Peršec, Jasminka AU - Ollivere, Luke AU - Ollivere, Benjamin J. AU - Yan, Huadong AU - Cai, Ting AU - Aithal, Guruprasad P. AU - Steves, Claire J. AU - Kantele, Anu AU - Kajova, Mikael AU - Vapalahti, Olli AU - Sajantila, Antti AU - Wojtowicz, Rafal AU - Wierzba, Waldemar AU - Krol, Zbigniew AU - Zaczynski, Artur AU - Zycinska, Katarina AU - Postula, Marek AU - Lukšić, Ivica AU - Čivljak, Rok AU - Markotić, Alemka AU - Brachmann, Johannes AU - Markl, Andreas AU - Mahnkopf, Christian AU - Murray, Benjamin AU - Ourselin, Sebastien AU - Valdes, Ana M. AU - Horcajada, Juan P. AU - Castells, Xavier AU - Pascual, Julio AU - Allegri, Massimo AU - Primorac, Dragan AU - Spector, Tim D. AU - Barrios, Clara AU - Lauc, Gordan PY - 2021 M3 - Original Research TI - Effects of Environmental Factors on Severity and Mortality of COVID-19 JO - Frontiers in Medicine UR - https://www.frontiersin.org/articles/10.3389/fmed.2020.607786 VL - 7 SN - 2296-858X N2 - Background: Most respiratory viruses show pronounced seasonality, but for SARS-CoV-2, this still needs to be documented.Methods: We 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.Findings: Meta-analysis of the mortality risk in seven European hospitals estimated odds ratios per 1-day increase in the admission date to be 0.981 (0.973–0.988, p < 0.001) and per increase in ambient temperature of 1°C 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 the 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.Interpretation: Severity of COVID-19 in Europe decreased significantly between March and May and the seasonality of COVID-19 is the most likely explanation. ER -