Coronavirus: Globally, tally of recovered closely follows total cases, with 14-day lag
Mapping the number of COVID-19 patients who recovered against the global case load reveals an interesting trend – it mimics the exponential growth curve of the pandemic, but also appears to closely trail the caseload, with a 14-day lag.
Absolute numbers on a particular date of the number of positive COVID-19 cases and recovered cases may still look intimidating. A two-week reflection, however, shows the recovery rate is trailing not too far behind the caseload.
For example, the Johns Hopkins database suggests 2,92,467 recovered cases Tuesday as against a global load of 1,365,004 cases. Two weeks ago, the caseload was 3,78,235, JHU statistics show.
Over a month back, March 1 saw 88,369 cases globally with only 42,716 recoveries. However, two weeks later, on March 15, there were 76,034 recoveries.
In other words, for roughly two months (from March 1 to April 6), recovered numbers grew exponentially, and clearly trailing the case load with a lag of 14 days (the incubation period).
Explaining this trend, Sitabhra Sinha, a scientist at the Institute of Mathematical Sciences in Chennai said, if everyone who fell sick on Day 1 recovered 14 days later, the two curves would exactly align. The discrepancy between the two is either people who fell sick and died, or people who recovered earlier or later than the mean period of 14 days.
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“Given that people are as likely to recover earlier as later, these two effects should balance out, so as to not affect the coincidence of the two curves by much,” he explained. “So that leaves only accounting for those who died… This is probably why the recovered curve is lower than the infected curve in your figure.”
While other pandemics might have a different duration interval between infection and recovery, “possibly one can conclude that the variability of this interval for different people is relatively low for COVID19.” Sinha has modeled a current estimated transmission rate for the country at 1.83. This means that each infected person in India is transmitting it to an average of 1.83 people.
As on Tuesday, the total number of COVID-9 deaths globally was 78,269.
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