Evaluating temperature and humidity gradients of COVID-19 infection rates in light of Non-Pharmaceutical Interventions

We evaluate potential temperature and humidity impact on the infection rate of COVID-19 with a data up to June 10 ^th 2020, which comprises a large geographical footprint. It is critical to analyse data from different countries or regions at similar stages of the pandemic in order to avoid picking up false gradients. The degree of severity of NPIs is found to be a good gauge of the stage of the pandemic for individual countries. Data points are classified according to the stringency index of the NPIs in order to ensure that comparisons between countries are made on equal footing. We find that temperature and relative humidity gradients don’t significantly deviate from the zero-gradient hypothesis. Upper limits on the absolute value of the gradients are set. The procedure chosen here yields 6 10 ^{−3 °} C ⁻¹ and 3.3 10 ⁻³ (%) ⁻¹ upper limits on the absolute values of the temperature and relative humidity gradients, respectively, with a 95% Confidence Level. These findings do not preclude existence of seasonal effects and are indicative that these are likely to be nuanced.