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R Number Rising in All Four Big Metros of India, Analysis Finds

R Number Rising in All Four Big Metros of India, Analysis Finds

A healthcare worker in PPE collects a swab sample from a resident during a testing campaign for COVID-19 in Mumbai, February 23, 2021. Photo: Reuters/Francis Mascarenhas

  • Delhi had the highest R number until the week ending December 15, of 1.12 – followed by Mumbai (1.10), Bengaluru (1.07), Kolkata (1.05) and Chennai (1.04).
  • Sitabhra Sinha, who estimated these values, cautioned that the numbers couldn’t be linked to the omicron variant because there are currently too few cases of the latter.
  • He also said the national R number briefly rose to greater than 1 – indicating a spreading outbreak – in August-September 2021.

New Delhi: The basic reproductive number, a.k.a. the R number, is on the rise in all four major metropolitan centres of India, indicating that the number of coronavirus infection cases is rising in urban areas, according to an analysis by Sitabhra Sinha, a theoretical physicist and senior faculty member at the Institute of Mathematical Sciences, Chennai.

Sharing his results with The Wire Science, Sinha said the trend has been consistent for the last two weeks at least – while at the same time cautioning that it couldn’t be linked directly to the omicron variant.

The R number indicates the number of people to whom the virus could be transmitted from one infected person. If its value is lower than 1, it means the virus is spreading from one infected person to less than one other person, i.e. the spread is declining. If the number’s value is greater than 1, it indicates a rising number of cases and an expanding outbreak, he said.

For example, if the R number is 1.1 and there are 100 cases, then the virus will get transmitted from them to another 110 people, and from these 110 to 121 more, and so forth.

On the other hand, if the R number is 0.95 and there are 100 cases to begin with, then the virus will get transmitted from to infect 95 more. Those 95 will, in turn, infect another 90 people, and thus the number of new cases will continue to decline.

Of India’s four major metropolitan cities, Delhi had the highest R number for the week ending December 15, according to Sinha’s analysis: 1.12, lower by 0.04 than it was in the previous week.

“For metros, it is slightly hard to say if a trend is consistent,” Sinha told The Wire Science. “The smaller the area for which I do estimation, the more likely it is going to change very quickly, because a smaller number means [higher] fluctuations.” So the situation on the ground could suddenly improve or deteriorate in the near future.

The next highest R number was found in Mumbai (1.10), followed by Bengaluru (1.07), Kolkata (1.05) and Chennai (1.04). Pune, which Sinha categorised as a metropolitan centre as well, the latest R number is at par with Delhi at 1.12.

Sinha also determined the R number for Maharashtra as a whole to be very close to 1. His calculation estimated it was 0.97 but he said there were discrepancies in the state’s case load data.

“Most districts of the state, including Mumbai, Pune, Nashik, Thane and Ahmednagar, have an R number greater than 1,” he explained. “It is unlikely that a handful of those districts that have an R number lower than 1 will balance out [for] the overall R number of the state [to be] below 1.”

He also estimated the value of the R number in states that currently had more than 1,000 active cases of novel coronavirus infections until the week ending December 15. All the calculations are for the week ending December 15.

And overall, India’s R number remained steady at 0.94 over the last two months.

Also read: Still Unconvinced of Imminent Need for Booster Doses: Govt Officials

He cautioned that none of these numbers could be linked, irrespective of surges in states, to the omicron variant simply because there are too few cases of this variant in the country – 109 – to lend itself to meaningful analysis. “Delta may still be driving” any surges, he said.

“As a matter of fact, R number rose to more than 1 … for a short period of time in August-September this year and this didn’t get much media attention at that time,” he added. “If an inconsistent rise in R number makes one believe that it is a sure pointer of a full-blown wave, then we should have had one in August-September too.”

That is, there is no reason to worry but the situation on the ground demands us to keep a close watch. And the worst thing we could do right now is to go easy on COVID-appropriate behaviour.

Public health expert and epidemiologist Chandrakant Lahariya also agreed with Sinha’s assessment, that assigning any relationships between the omicron variant and small surges at this time wouldn’t be scientifically correct. And both Sinha’s and Lahariya’s views are finding basis in numbers from the UK. The UK is currently reporting more than 80,000 new coronavirus infections per day – but only 2.4% of which are of the omicron variant, according to Our World in Data.

Lahariya wasn’t surprised by Sinha’s estimated R number values in the major metropolitan centres being greater than 1. He said that these cities are better connected and as a result their respective case loads have always been higher, and the virus’s spread percolates from these centres to others and finally to the hinterland, he added.

He also said the need of the hour isn’t to ramp up testing, perhaps just to demonstrate an increase in the number of tests, but to test strategically. “Use data. Identify where the transmission is higher. Go for aggressive testing there. Ensure results in a day or less,” he explained.

He added that such a strategy would be less concerned with whether an individual is ‘positive’ or not and more with preparing “hospital infrastructure accordingly, looking at trends. That is how testing data is utilised from a public health perspective.”

He also cautioned against what he called “sub-optimal science communication from the government”. Until a few months ago, when there were no signs of a third major outbreak of COVID-19 in the country, the government periodically issued messages that a ‘third wave’ was still impending. This sort of communication, Lahariya said, could make common people lose confidence in the alarm bells when they are actually sounded – a case of the shepherd crying wolf.

Irrespective of any uncertainty, masking up, getting fully vaccinated and following COVID-appropriate behaviour are the best tools we currently have to fight any eventuality, he finished.

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