Rhythmic components of COVID-19 daily cases in various countries

Not only does COVID-19 pandemic encourage scientists to look for remedies and treatment schemes, but also identify the drivers of pathogenicity and spread of the virus. The scope of this research consisted in identifying recurrence patterns and comparing the number of daily cases between various countries. Data for countries where at least 500 daily cases were recorded at least once (17 in Europe, 3 in North America, 7 in South America, 3 in Central America, 17 in Asia and 3 in Africa). According to our evaluation, the dynamics recorded for 25 countries includes a 7-day statistically significant component. This statistically significant weekly component has been identified in 76% of the countries examined in Europe, 66% in North America, 71% in South America, and 18% in Asia. The range of this rhythmic component is low at the growth stage and increases at the stabilization and decrease stages. The weekly phases feature shifting peaks depending on the country. In some cases, the phases shift, i.e. they are not limited strictly to certain days of the week. Due to range and phase variation, its explanation cannot be limited to strictly medical and social factors. In some cases, national incidence dynamics includes 3, 4, 6, 8 and 10-day periods. Understanding the factors of recurrence patterns in COVID-19 incidence dynamics may help in the pandemic response.