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Explained: India's Covid 'r' value is over 1.0. What is it?
Covid ‘r’ value explained: ‘R’ value is a mathematical term used to track the virus and predict how it may spread in a given area.
India's effective 'r' value, or the rate at which the coronavirus is spreading, has gone above 1.0 for the first time in three months, a researcher from Chennai's Institute of Mathematical Sciences told news agency PTI. 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 told PTI.
The last time the 'r' value was above 1.0 was between January 16-22.
"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 all major cities - Mumbai, Bengaluru and Chennai - are showing 'r' values above 1. In fact, for Delhi and UP it is over 2.0, Sinha said.
What is 'r' value?
The 'r' factor, or 'R0 (pronounced 'R-naught') is the virus' rate of reproduction.
Scientists use this term to track the virus 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 infected person will likely infect another.
That said, it is important to remember these values are not an 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.
A 'r' number lower than 1 indicates the disease will soon stop spreading as there aren't enough people being infected to sustain the outbreak.
READ: 1.98 lakh cases in Germany, Shanghai eases curbs, spike in India: Global updates
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 number of deaths, hospital admissions and, of course, the number of samples testing positive for Covid-19.
Is the 'r' number accurate?
Not entirely. While it is an important metric in the fight against Covid-19, experts 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 Nature.com article published in July 2020, during the start of the pandemic.
Among the reasons for caution are 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.
With input from PTI
