Explained: India’s Covid ‘r’ value is over 1.0. What is it, why is it dangerous?

India’s effective ‘r’ value, or the rate at which the coronavirus is spreading, has gone above the danger level of 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 – when India was reaching the peak of the third wave of infections and there were over 2 lakh new cases daily. 

“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. 

Highly contagious diseases – like measles – will have very high ‘r’ values; for measles it is often cited at 12-18.

The coronavirus is believed to have an ‘r’ value of around 3, the BBC reported in March last year, assuming no action is taken to stop it spreading. 

Notwithstanding that, experts and the government have repeatedly cautioned that an ‘r’ over 1.0 is cause for concern.

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.

The ‘r’ was highest this year in January – a frightening 2.98, PTI reported.

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.

So, if the ‘r’ value is above 1.0, are cases rising?

The short answer is yes. 

India’s daily Covid figures crossed 2,000 for the second time this week and today’s 2,067 new cases were a 66 per cent increase from Tuesday.

Cases have also spiked in Delhi, with the national capital reporting over 600 positive Covid cases in 24 hours for the first time since February.

This prompted a meeting of the disaster management agency, which re-introduced mandatory masking and ordered violators to pay a fine of ₹500. 

READ: Schools to stay open, ₹500 fine for no mask – Delhi’s new Covid rules

Masking has already been made mandatory (again) in a few other states.

However, it is important to remember that just because the ‘r’ value has crossed 1.0 it does not mean a fourth wave of infections is upon us.

The ‘r’ value is an indication – a red light – that there is reason to worry.

Proper masking, attention to Covid-appropriate behaviour, and double vaccination (with a precautionary third dose for those eligible) is highly recommended by all experts to help stay safe from 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