Covid-19 growth rate dips in Bengaluru, says professor

BENGALURU: The effective reproduction number of Covid-19 — the mean number of infections caused by a single infected person at this stage of the pandemic — in Bengaluru has not only dipped since July, but also appears to be in control, according to a professor from the Institute of Mathematical Sciences, Chennai.
The city’s effective reproduction number (or simply R) fell below 1 between August 2-5, but has increased slightly since then.

“As any intervention normally takes between 10 days to two weeks to show up in the incidence data, the improvement of the situation in Bengaluru is the fruition of efforts put in place by July 18 or so,” said Prof Sitabhra Sinha, professor with the institute, who has authored a paper titled ‘Epidemiological Dynamics of Covid-19 in India’.
Incidentally, there was a lockdown in place in Bengaluru and several other districts from the night of July 14 to the early hours of July 22, which possibly resulted in the drop in R.
R is considered the rate of growth of the pandemic. Sinha says the reproduction number has to be greater than 1 for an epidemic to occur, and larger the number, the faster the disease spreads.
In Bengaluru Urban, the R was almost 1.4 between July 4 and 23. It fell slightly to 1.2 during July 25-29. By August 2-5, it further reduced to 0.8. For the more recent period, it has increased slightly above 1, said Sinha. In Karnataka overall, the R value is 1.1 for the period of August 5-8.
In India, the R value was marginally above 1 between August 1 and 6. In their latest data, both Mumbai and Chennai have the value below 1, while Delhi, which had a value lower than 1 for nearly a month, has now increased to 1.08. Kolkata also has a figure above 1. In several other states, the values continue to be over 1 (see box).
In order to understand how the value of R ranged in other countries when the pandemic peaked, the value was 2.6 in the US in March, 2.7 in Italy in last week of February and 4.8 in Turkey in the third week of March.
R is affected by measures like lockdown and other social distancing norms adopted by states and countries. The paper points out that the growth rate of the disease continued to be low despite lockdown norms being lifted to a large degree.
“As India is still very far from achieving herd immunity, and there appears to be no evidence that the pathogen has shown any change in its ability to infect, it is possible that the voluntary adherence to public hygiene has been responsible,” the paper states. “If true, this may suggest that, under certain conditions, citizens can be mobilized to engage in a mass effort to achieve desirable public health outcomes.”