Thursday 26 May 2022
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R-value of India shoots above 1, Delhi’s above 2 after 3 months

The R-value, alternatively called the r factor or R0 (pronounced 'R-naught'), is the number of people someone infected with the virus during an epidemic infects on an average

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The R-value — the number of people a patient infects on an average during a pandemic — has gone above 1.0 for the first in three months, with the most dangerous statistic coming from the national capital where it has shot up to 2.12, a researcher from Chennai’s Institute of Mathematical Sciences said. It was 1.07 for the period April 12-18 — up from 0.93 for April 5-11. The number has been increasing steadily, the researcher, Sitabhra Sinha said.

The last the R-value was above 1.0 was between 16 and 22 January. “This increase is not just because of Delhi but also Haryana and Uttar Pradesh,” Sinha, who has been tracking R-values for India since the pandemic began, said.

Almost every major city — Mumbai, Bengaluru and Chennai — is showing an R-value above 1. In fact, for Delhi and UP it is over 2.0, Sinha said.


The R-value, alternatively called the r factor or R0 (pronounced “R-naught”), is defined also as the rate of reproduction of a virus. Scientists are using this term to track the coronavirus in the case of the current pandemic and predict how quickly it may spread in a given geographical area, which makes it critical to combating Covid-19. The ‘R’ stands for the number of people one person can infect. Therefore, a value of 1 means every patient is infecting another person.

That said, it is important to remember these values are not absolute and depend on myriad other factors that may hasten or slow the spread.

What should the R-value be?

Ideally, the R-value should be as far below 1.0 as possible.

An R-value lower than 1 indicates the will soon stop spreading as there aren’t enough people being infected to sustain the outbreak.

How is the R-value calculated?

Since you can’t actually identify the moment any one individual is infected, scientists usually work backwards using data like the number of deaths, hospital admissions and, of course, the number of samples testing positive for Covid-19.

Is it accurate?

Not entirely. While it is an important metric in the fight against Covid-19, caution against trusting it too much.

This is because it is an “imprecise estimate”, according to Jeremy Rossman, a virologist with the United Kingdom’s University of Kent. Quoted in a article published in July 2020, during the start of the pandemic.

Among the reasons for caution is the fact the ‘r’ can spike up and down even when case numbers are low. Importantly, since it is an average for a population, it could hide localised variations that, in a country as large as India, may be key.

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