R-value exceeds 2 in Delhi, Mumbai; indicates faster spread of coronavirus

As coronavirus cases spiral, the 'R-value', which indicates how rapidly the virus is spreading, has crossed two in Delhi and Mumbai, researchers said on Thursday. Chennai, Pune, Bengaluru and Kolkata have R-value (or reproduction number) of over 1, as per the data study by the researchers of the Institute of Mathematical Sciences, Chennai. Sitabhra Sinha, who led the study, said the R-value of Delhi stood at 2.54 between December 23-29, while for Mumbai it was 2.01 between December 23-28. Both these cities have seen an exponential rise in cases. Pune and Bengaluru recorded R-value of 1.11.

The R-value of Kolkata and Chennai was 1.13 and 1.26, respectively. "Since mid-October, the R-value of all these cities was over 1. What is new was the sudden rise. The fact that Delhi and Mumbai crossed the R-value 2 is quite surprising," Sinha told PTI. Delhi on Wednesday reported a massive jump in daily COVID-19 infections with 923 fresh cases, the highest since May 30 and 86 per cent up from a day earlier.

The positivity rate in Delhi crossed 1 per cent after six months to reach 1.29 per cent. On December 20, 91 new COVID-19 cases had been recorded in the national capital, but the figure climbed to 923 on Wednesday. The COVID-19 positivity rate in Delhi thus jumped to 1.29 per cent from 0.19 per cent between December 23 and December 29. Similarly, Mumbai on Wednesday reported 2,510 COVID-19 cases, the highest daily addition since May 8, 2021, besides one death.


On December 20, only 283 cases had been reported in Mumbai, whereas on Tuesday the financial capital of the country recorded 1,377 cases, and on Wednesday the figure went up by 80 per cent. The Reproduction number or R refers to how many people an infected person infects on average.

In other words, it tells how 'efficiently' a virus is spreading. An R value of less than 1 denotes that the disease is on decline. Conversely, if R is greater than 1, it means the number of infected people is increasing in each round -- technically it becomes the 'epidemic phase'.