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. Currently at 1.07 for the period April 12-18 - it was 0.93 in April 5-11 - it has been increasing steadily, 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 beginning of the pandemic, told PTI.

What is 'r' value?

The 'r' factor, or 'R0 (pronounced 'R-naught') is the rate of reproduction of a virus.

This is a mathematical term scientists can use 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 individual will infect another. Highly contagious diseases - like measles - will have very high 'r' valies; for measles it is often cited at 12-18.

The coronavirus - officially called Sars-CoV-2 - is believed to have an 'r' value of around 3, 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.

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, number of hospital admissions and, of course, the number of samples (and people) testing positive for Covid-19.

So, if the 'r' value is above 1, 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-introdced mandatory masking and ordered violators to pay a fine of ₹500. Masking has already been made mandatory (again) in a few other states, including those bordering Delhi.

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 a potential uptick in cases.

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.