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. 2021 Jan 21;11:1981. doi: 10.1038/s41598-021-81419-w

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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(A) Survival of the active SARS-CoV-2 fraction after 30 min of solar UV insolation as a function of τ₉₀. (B) Solid black line: acute respiratory track infection (ARTI) risk during cold and influenza epidemics as a function of the 25(OH)D concentration (reprinted from³ according to the CC BY 4.0 licence terms (https://creativecommons.org/licenses/by/4.0/); red and blue curves: power exponential (Eq. 8) and first point monoexponential fits added by the present author. In both graphs, the corresponding date runs from left to right. (C,D) Blue curve: corresponding new daily cases to (A,B) obtained by numerically integrating Eq. (4) (see excel file). In both integrations, k₀ was fitted to obtain a typical threefold increase in the last 10 days (see Fig. 1), and ρ was neglected (surge phase). Black curve: mono-exponential curve.