CoViD-19: Weekly Mortality Cycle and Sunday Protective Phenomenon

Background. The Weekly Mortality Cycle among CoViD-19 patients has been studied. Methods. Mortality data obtained from the 'Worldometer' website were analyzed with a comparison of absolute values, percentages, and p-value. Results. For patients suffering from CoViD-19, the most favorable or the safest days of the week were Sundays and Mondays. Conclusion. The weekly cycle with decreased mortality on Sundays and Mondays is a unique phenomenon observed among victims of CoViD-19. Presumably the decreased mortality on certain days of the week related to the optimized therapeutic protocols used on the "safest days".

Diagnostic kits to identify SARS-CoV-2 infected patients became available beginning of January 2020. 3 Since then, statistics related to the new disease became available for analysis. 6 In the first report provided by a group of experts from Imperial College London, there were 41 confirmed cases with 2 deaths; the estimated number of infected people was 1,723, 7 (the estimated mortality rate was around -0.12 %). In the second report provided by the same group of experts, there were 440 confirmed cases with 9 deaths, and the estimated number of infected people was around 4000, 8 (the estimated mortality rate was around -0.23 %). According to the subsequent studies, the mortality rate among SARS-CoV-2 infected people is less than 1 %, 9 and can vary around 0.3-0.5 %. 10 Collection of the date dealing with the current pandemic should be done with great care otherwise coronavirus mortality overestimation can lead to wrong decisions. 11

Challenges of CoViD-19 Pandemic.
From the first days of the pandemic outbreak, it became clear that disease-oriented approach in medicine, which had been used successfully to cope with the task of stabilizing the symptoms encountered in the case of chronic diseases, had limited value when the new acute infectious disease emerged.
It is well known that acute disease is not a stable and constant pathological condition, but it has several phases, and each of them requires different medication and care. Therefore, it is not logical to look for a drug for the treatment of CoViD-19 in general, but it is reasonable to look for groups of medications that could be effective to treat various phases of this disease.
Due to the fact that CoViD-19 is a new disease, world public health care had to start new clinical trials to find medicines that could be safe and effective in treating patients with CoViD-19 and comorbidities. As a result, all people infected with SARS-CoV-2 have been automatically converted into participants for the most extensive clinical trials in the history of mankind. Efficacy of these trials can be analyzed on the basis of global and local statistics.

A Global Weekly Mortality Cycle related to CoViD-19.
Background: On the CoViD-19 mortality statistics presented on the 'Worldometer' website, 6 a weekly cycle of decreased mortality on Sundays and Mondays is evident (Fig. 1). This cycle can vary in different countries, 12 but the main trend is decreased mortality towards weekends. 13 Objective: To study weekly mortality cycle among CoViD-19 patients.
2.1. Methods: Since July 6, 2020, data from 'Worldometer' website were collected every 5-6 days in the form of numbers and screenshots. The date when information was collected is given in the text.

The Weekly Mortality Cycle related to CoViD-19 in Various Countries.
Background: The global trend that may be termed the "Weekly Mortality Cycle" with more or less certainty, has been revealed in various countries including Brazil, Chile, Germany, Mexico, Russia, the United Kingdom and the United States of America. As it was presented above, the lowest worldwide mortality due to CoViD-19 was on Sundays and Mondays. In various countries days of the week with the lowest mortality can vary nevertheless they either belong to the weekend or they are near the weekend.
Due to the fact that the time of CoViD-19 outbreak varied in the different countries, the analysed weeks varied too. All analysed periods started on a Sunday and ended on a Saturday.

Methods:
The data on mortality from CoViD-19 in different countries were taken from the site 'Worldometer'. 14 A comparison of the total mortality on certain days of the week in absolute values and percentages in various countries was carried out (Table 3).
Results: A comparison of the total mortality on certain days of the week has revealed that in the analysed countries daily mortality on Sundays or Mondays was less than on other days of the week, excluding Chile, where the lowest mortality due to CoDiD-19 was on Tuesdays. The highest HLM ratio was in Chile (2.70), the lowest one was in Russia (1.57).
Conclusion: For patients suffering from CoViD-19, the safest days of the week were mostly Sundays or Mondays.

"Sunday Protective Phenomenon" and "Monday Protective Phenomenon".
There are several combinations of days with the lowest mortality, but the most common are Sundays and Mondays. These may be termed "Sunday Protective Phenomenon" (  In some countries analysis of the daily mortality in July (2020), revealed a stable weekly cycle with the one and the same day of the lowest mortality being either Sunday ( The United States of America (29.03-01.08): On Sundays, the daily mortality was less than on Tuesdays, Wednesdays (p<0.001), Thursdays, Fridays (p<0.005), and Saturdays (p<0.05). On Mondays, the daily mortality was less than on Wednesdays (p<0.005), Tuesdays, Thursdays (p<0.01), and Fridays (p<0.05).
Germany (29.03-23.05): On Sundays, the daily mortality was less than on Mondays, Tuesdays, Wednesdays and Thursdays (p<0.05). On Saturdays, the daily mortality was less than on Wednesdays (p<0.05).  Mexico (19.04-01.08): On Mondays, the daily mortality was less than on Wednesdays, Thursdays, Fridays and Saturdays (p<0.005). On Tuesdays, the daily mortality was less than on Wednesdays, Thursdays, Fridays and Saturdays (p<0.05). On Sundays, the daily mortality was less than on Wednesdays and Thursdays (p<0.05).

Conclusion:
The weekly mortality cycle was discovered in Brazil, Chile, Germany, Mexico, Russia, in the United Kingdom and United States of America. In majority of these countries, for patients suffering from CoViD-19, the safest days of the week were either Sundays or Mondays. In Chile, the safest days of the week were Mondays and Tuesdays (Table 3).

The Weekly Mortality Cycle in the States of the United States with the highest mortality.
Background: Due to the fact that the United States had the highest numbers of death related to CoViD-19, 14   Methods: There were comparisons between the total mortality on certain days of the week in absolute values, percentages and a calculation of HLM ratio (

Revision of some numbers dealing with mortality due to CoViD-19.
In several countries after revision of death record related to CoViD-19, some amount of the fatal cases were added, and this fact can be recognized as a sharp spike of deaths in the daily mortality chart.
Sudden increase of death number happened in China on April 17, 2020, when 1,290 new fatal cases were added (Fig. 6). 15 The local authorities provided the following explanation: "The revisions were made in accordance with related laws and regulations, as well as the principle of being responsible for history, the people and the deceased". 16 There was also an opposite correction that took place in France: a number of CoViD-19 victims was decreased by 217 cases on May 19, 2020. 20

Updating Global Mortality Data and Weekly Mortality Cycle related to CoViD-19.
Background: During the current observation death numbers on the 'Worldometer' website related to the whole world and to the various countries were updating constantly.
Objective: To study if updating and correction of the mortality data affects the global weekly mortality cycle related to CoViD-19.

Method:
In order to know if the correction of the data for the past days affects the results of the current study, new data were collected on September 20, 2020 (Table 7).
There were comparisons between the total mortality on certain days of the week in absolute values and percentages, calculation of HLM ratio, and the comparison of the daily mortality between various days of the week with the calculation of the p-value. 34 weeks were analysed (26.01.20-19.09.20). Conclusion: For patients suffering from CoViD-19 worldwide, the safest days of the week were Sundays and Mondays (Fig 7). Updating global mortality data didn't affect results of the study.  (Table 8). Results: During the current study the total numbers of deaths related to the time frame between January 26 and July 4, 2020, were not stable. There was a fluctuation of the death numbers in the various days of the week, nevertheless the lowest numbers of deaths were on Sunday and the highest numbers of deaths were mostly on Thursday. A ratio between the death numbers on Thursday and Sunday decreased from 1.485, on July 12, to 1.458, on September 7.

Method:
In order to know how update of the database affects the absolute values of the total global mortality and mortality on the various days of the week, a comparison of death numbers for other 18 weeks (29.03.20 -01.08.20), obtained at the different dates, has been done (Table 9). countries was carried out. Then a comparison of the new results with the results obtained on August 10, 2020 (Tables # 4-6) was done. The difference in the total death numbers presented as + / -Δ.   the lowest daily mortality was changed from Sunday to Wednesday (Fig. 8).   (Fig. 9).

A Weekly Cycle relates to the Human Civilization.
In the 18th century, Antoine-Yves Goguet wrote: "We can consider as the first step that men have taken to obtain a measure of time, was the establishment of the small period of seven days, which bears the name of the week. We see that, from time immemorial, it has been used by almost all peoples, and that the arrangement has been perfectly uniform". 21 Our contemporary, Joseph Needham, expressed a modern view on the calendar and said, that some of its elements are based on those astronomical cycles which have obvious importance for man, such as the day, the month and the year; others are artificial, such as the week and the subdivisions of the day. 22 Eviatar Zerubavel, describing the characteristics of the weekly cycle, titled his book "Hidden Rhythms". 23

Discussion.
On the one hand, a week as a time frame obviously exists, but on the other, there is no natural basis that could explain a weekly cycle.
As described above the weekly mortality cycle with the trend towards decreased mortality on weekends is a unique phenomenon that has been observed among victims of CoViD-19. It has an opposite pattern compared to increased hospital mortality on weekends in the United Kingdom discussed in 2015. 24

Conclusion.
It is vitally important to recognize factors which formed the basis of decreased mortality on Sundays, Mondays and some other "safest days" of the week. These factors can relate to various aspects of healthcare, including therapeutic protocols and work schedules, or to human habits and traditions. Presumably, they relate to the optimised therapeutic protocols used on the "safest days".
If the factors, which reduced mortality on certain days of the week, could be identified, their positive effect should be spread to other days of the week. As a result many lives of CoViD-19 patients could be saved in future.

Acknowledgment:
I am grateful to my colleagues from Brazil, China, Italy, Malaysia, and the USA who shared with me therapeutic protocols used at their hospitals for CoViD-19 patients.

Disclosure Statement:
The author declares there are no any conflicts of interest in the submitted manuscripts.

Final Remark:
The first study on the Weekly Mortality Cycle among CoViD-19 patients was completed on Aug 1, the second one was completed on Aug. 14, the last study was completed on Sep 21, 2020.
A manuscript of the second study was sent to my colleagues living in different countries. From that time they began their own investigations on their places.