The impact of seasonal factors on the COVID-19 pandemic waves

The daily number of new COVID-19 cases per capita is an important characteristic of the pandemic dynamics indicating the appearance of new waves (e.g., caused by new coronavirus strains) and indicate the effectiveness of quarantine, testing and vaccination. Since this characteristic is very random and demonstrates some weekly period, we will use the 7-days smoothing. The second year of the pandemic allows us to compare its dynamics in the spring and the summer of 2020 with the same period in 2021 and investigate the influence of seasonal factors. We have chosen some northern countries and regions: Ukraine, EU, the UK, USA and some countries located in tropical zone and south semi-sphere: India, Brazil, South Africa and Argentina. The dynamics in these regions was compared with COVID-19 pandemic dynamics in the whole world. Some seasonal similarities are visible only for EU and South Africa. In 2020, the southern countries demonstrated the exponential growth, but northern regions showed some stabilization trends.