Climatic Influence on COVID-19: Investigating the Role of Temperature and Humidity in the Spread of the Omicron...

Understanding how climate modulates infectious disease dynamics is critical for anticipating epidemic patterns. After a hot debate on potential facilitation of population spread by climate factors during the first 2 years of the COVID-19 pandemics, not much attention has been devoted to assess whether the ensuing SARS-CoV-2 waves also displayed similar climatic facilitation, or conversely, whether immunity dismissed any such forcing and potential signatures. This study examines the association between climatological variables-specifically temperature and absolute humidity (AH)-and the global incidence of the SARS-CoV-2 Omicron variant (B.1.1.529) during its massive epidemic wave (2021-2022). Using global-scale epidemiological and climate data, we applied the scale-dependent correlation analysis to identify transient, scale-specific non-linear associations between factors and the disease across regions. We found consistent significant local negative correlations between incidence and both temperature ( $r_s=-0.4$ to $-0.6$ ) and AH ( $r_s=-0.3$ to $-0.5$ ), particularly in mid-latitudes during colder months. Threshold analyses revealed temperature and humidity ranges of 12°C-21°C and 8-12 g $m^{-3}$ , respectively, where transmission was most favored, fully in line with previous results obtained for the first COVID-19 variants. A stochastic population-based model incorporating a temperature-modulated infection rate reproduced epidemic dynamics more accurately than constant or seasonal formulations, reducing normalized residuals by approximately 40%-50%. These results largely demonstrate a robust climatic influence also on Omicron transmission yet underscoring the value of integrating environmental drivers into epidemic modeling and early-warning frameworks.