Abstract
The Covid-19 pandemic has required nonpharmaceutical interventions, primarily physical distancing, personal hygiene and face mask use, to limit community transmission, irrespective of seasons. In fact, the seasonality attributes of this pandemic remain one of its biggest unknowns. Early studies based on past experience from respiratory diseases focused on temperature or humidity, with disappointing results. Our hypothesis that ultraviolet (UV) radiation levels might be a factor and a more appropriate parameter has emerged as an alternative to assess seasonality and exploit it for public health policies. Using geographical, socioeconomic and epidemiological criteria, we selected twelve North-equatorial-South countries with similar characteristics. We then obtained UV levels, mobility and Covid-19 daily incidence rates for nearly the entire 2020. Using machine learning, we demonstrated that UV radiation strongly associated with incidence rates, more so than mobility did, indicating that UV is a key seasonality indicator for Covid-19, irrespective of the initial conditions of the epidemic. Our findings can inform the implementation of public health emergency measures, partly based on seasons in the Northern and Southern Hemispheres, as the pandemic unfolds into 2021.
Highlights
Problem: One of the most crucial questions for the management of the Covid-19 pandemic has been whether the epidemic would exhibit a consistent seasonality pattern [1]
Incidence rates are influenced by human activity, a fact reflected in mobility data released to fight Covid-19 spread and taken into consideration in all subsequent analyses to mirror restrictive measures
The seasonality effects of Covid-19 were exclusively dealt with using UV radiation levels and mobility information that reflected the period of the year and restrictive measures, respectively (Figure 1)
Summary
Problem: One of the most crucial questions for the management of the Covid-19 pandemic has been whether the epidemic would exhibit a consistent seasonality pattern [1]. As the pandemic has engulfed the globe, affecting human activities on an unprecedented level, and concerns that Covid-19 may become endemic in the entire population, as other coronavirus infections have [4], the issue of seasonality must be unambiguously settled, especially as we are approaching a full year of the epidemic expansion [7] Other factors such as population density [8] or public health measures [9] have been seen as critical and challenged notions of seasonality of Covid-19, intertwined with irregular seasonal parameters such as humidity and air temperature [10]. Detailed forward simulations based on the first half of 2020 indicate that UV levels may influence Covid-19 growth rates [15] These studies have provided the first compelling evidence for seasonality of Covid-19 connected to UV levels as the ultimate parameter that signals seasons or day length, concurrently for winter/summer cycles in the Earth’s hemispheres
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