key: cord-0307217-np5pq27d authors: Nesteruk, I.; Rodionov, O.; Nikitin, A. title: The impact of seasonal factors on the COVID-19 pandemic waves date: 2021-08-14 journal: nan DOI: 10.1101/2021.08.06.21261665 sha: b14f030ee27325ab34e7c225925fa2bf70817876 doc_id: 307217 cord_uid: np5pq27d 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 2021, the southern countries demonstrated the exponential growth, but northern regions showed some stabilization trends. and averaged DCC values as follows: The slopes of DCC lines are different for different countries. The highest ones can be seen for USA and Ukraine (see Fig. 1 ) and for Argentina, Brazil, and South Africa (see Fig. 2 ). The number of cases in the whole world has increased not so intensively. The duplicated time of the accumulated number of cases was estimated 2.31 days for USA and 3.65 days for the whole word [6] . For the northern region, the DCC values started to decrease in June-July 2021respectively, indicating the end of the first pandemic waves. Unfortunately, releasing the quarantine limitations in the vacation season 2020 caused new pandemic waves in northern countries and regions (see "crosses" in Fig. 1.) . Especially intensive growth of DCC values can be seen for USA and is probably connected with mass protests and ignoring the social distance in this country. Table 1 . "Triangles" correspond to the DCC values calculated for 2021 with the use of eqs. (1), (2) and Table 2 . After some stabilization in April-May 2020, the DCC numbers for the whole world started to increase almost exponentially (see corresponding black "crosses" in Fig. 1 or 2. ) In southern region in April-June 2020, the DCC numbers continue to increase almost exponentially with the almost equal slopes, smaller than in March 2020 but much intensively than in the whole world. Probably these differences in the "northern" and "southern" dynamics are connected with the cold or rainy seasons and neglecting the quarantine restrictions in South. On the other hand, the pandemic dynamics in Brazil, Argentina and India significantly differ in 2020 and 2021 (compare "crosses" and "triangles" in Fig. 2) . The maximum of DCC values in India probably is connected with a new "delta" strain of coronavirus developed in this country. Probably, a new strain is responsible for almost exponential increase of DCC values in May-July 2021 in the UK (see the magenta "triangles" in Fig. 1 ). More or less similar seasonal behavior All rights reserved. No reuse allowed without permission. perpetuity. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in The copyright holder for this this version posted August 14, 2021. ; https://doi.org/10.1101/2021.08.06.21261665 doi: medRxiv preprint of DCC values we can see only in the case of EU and South Africa (corresponding yellow markers in Fig. 1 and magenta markers in Fig. 2 follow parallel lines in May-June 2020 and 2021). Table 1 . "Triangles" correspond to the DCC values calculated for 2021 with the use of eqs. (1), (2) and Table 2 . We can see in Fig. 2 South Africa on March 19, 2020 and March 23, 2020, respectively [7, 8] . The daily number of new cases stabilized and even decreased. Further pandemic dynamics in these countries showed smaller DCC values in comparison with Brazil, where no lockdowns and strict quarantines were used. Nevertheless, in July 2021 the DCC numbers in Argentina became higher than in Brazil and much higher than in South Africa (see Table 2 ). Nevertheless, we cannot conclude that the restriction policy in South Africa was the most effective, since these countries have different climate conditions and structures of population. Moreover, many COVID-19 cases were not identified and shown in Tables 1 and 2. The visibility coefficient (ratios of real and the registered number of cases) could be very different for different countries and time periods [9] [10] [11] . 2. Nesteruk I. COVID19 pandemic dynamics Coronavirus disease (COVID-2019) situation reports COVID-19 Data Repository by the Center for Systems Science and Engineering Early stages of epidemics and exponential growth Argentina announces mandatory quarantine to curb coronavirus". Reuters President Cyril Ramaphosa meets with political parties to combat Coronavirus COVID-19 Visible and real sizes of new COVID-19 pandemic waves in Ukraine Impact of vaccination and undetected cases on the COVID-19 pandemic dynamics in Qatar in 2021 The DCC values calculated with the use of (1), (2) and datasets presented in Tables 1 and 2 are shown in Figs. 1 and 2 for northern and southern regions, respectively. "Crosses" and (3)Where  and  are constant parameters, see ,e.g., [6] . Differentiation of (3) yields the exponential growth also for the DCC values, since according to (3):