The trend has held for too long — nine weeks in a row — for it to be a statistical quirk. For instance, fresh cases recorded this Monday were 22,007 — a big drop from Sunday’s tally of 24,976. In the previous week (June 28-29), Sunday’s count was 19,741, which dropped to 18,870 the next day.
TOI looked at data of daily Covid-19 cases since May and found that the “Monday dip” pattern has held on all 10 weeks during this period, except the very first Sunday-Monday (May 3-4).
The best explanation for why the case count falls every Monday lies in the testing figures. The number of tests conducted falls every Sunday, which then reflects on the number of cases detected on Monday, and sometimes on Tuesday as well, since the results of the RT-PCR tests take 24 to 48 hours to arrive.
According to the website Covid19India.org, 2.48 lakh tests were done last Saturday (July 4). The number fell to 1.8 lakh on Sunday and again rose to 2.41 lakh on Monday. Likewise, in the week before that, 2.31 lakh Covid tests were done on Saturday (June 27), 1.7 lakh the next day (Sunday) and 2.1 lakh on Monday (June 29). For each Sunday since June 6, for which data was available, testing numbers showed a dip.
Interestingly, daily figures for deaths don’t show any such pattern, again pointing to reduced testing on Sundays as the main reason for drop in case counts on Mondays. The “Monday dip” is another indicator of the close relationship between testing and detection of Covid cases, and why states need to ramp up testing.