Six months into the pandemic, is India over the first coronavirus peak?

Six months into the pandemic and over 6 million Covid-19 cases, India finally has some good news.

The reproduction rate or the R value of Covid-19 seems to have been under control, statistics show. The reproduction number is a way of rating the coronavirus' ability to spread.

According to the calculations done by the COV-IND Study Group, University of Michigan, USA, for the last one week, Covid-19 reproduction rate has stayed below 1, which means that a single virus carrier is infecting less than one person on average.

For the first time since the Covid pandemic hit the country, the virus' reproduction rate has come down to below 1 and stayed low for a long time.

Effectively, the situation is said to be under control when the R value stays below 1 for a minimum of two weeks.

According to the Michigan University's app, the overall R value of Covid-19 in India came down below 1, for the first time since the pandemic struck, on September 21.

"It seems to me that the virus curve has indeed taken an optimistic turn, I am encouraged by the national numbers because testing has increased substantially," said Bhramar Mukherjee, professor of epidemiology at the University of Michigan's Rogel Cancer Center told India Today.

The continuity of the R value to remain below 1 will define how well India has been able to control the virus.

But the good thing about the reduction in reproduction rate of the virus is that it has happened after India ramped up its testing.

In the last seven days since India's R value went down 1, the country carried out more than 7.5 million tests - which is more than a million per day.

Value of R less than 1 in high-burden states

The decline in the reproduction number for Covid-19 is reflective of a decrease in R value in several states, including the worst affected ones as well.

Data as on September 26 shows that nearly 14 big states in India now record an R value below 1. While the average R value in India was 0.95, there were nine states where this value was lower than the national average.

Even Maharashtra, the state which accounts for nearly 22 per cent of India's total Covid-19 cases, the latest R value recorded was 0.93, lower than the national average.

This simply means that 100 infected people in Maharashtra further infected 93 people, thus putting a speed breaker to the virus' exponential growth.

Andhra Pradesh recorded the lowest R value of 0.85 among the big states, followed by Uttar Pradesh (0.87) and Haryana (0.88).

Other states with a below national average R value include Punjab (0.90), Karnataka (0.91), Chhattisgarh (0.91), UT of Jammu and Kashmir (0.91), Assam (0.94), and Jharkhand (0.94).

The R value in Delhi, Bihar, Telangana and Tamil Nadu is also below 1 albeit they are above the national average of 0.96.

Kerala, once modelled as the best state for having controlled the pandemic, is performing the worst. The R value in Kerala has reached 1.35. This means that one infected carrier is infecting more than one person on average in the state.

Kerala has been recording over 6,000 new cases for the last four days. On Sunday it recorded 7,445 cases, the highest ever since the pandemic struck the state.

West Bengal, which has been mysteriously been recording close to 3,000 cases every day for the last month also has an R value of 1. This means that an infected person in the state is infecting exactly one more person, for the last three weeks.

Odisha (1.06), Gujarat (1.04), Rajasthan (1.09) and Madhya Pradesh (1.08) also record an R value above 1.

The curious case of high TPRs

India Today's Data Intelligence Unit (DIU) found that in most of the states where the R value is lower than 1, the test positivity rates (TPR) were high.

Test positivity rate is the percentage of people who test positive for the virus of those overall who have been tested.

Though the national average TPR is now moving downwards, in many states it is still way above the threshold level of 5 per cent.

This leads to the question - has the R value been impacted by low testing?

Maharashtra that has an R value of 0.93 also had a 20 per cent TPR, moving in an upward direction.

Gautam Menon, professor of Physics and Biology at the Ashoka University, Sonipat said, "Since the R is computed on the basis of the growth in detected cases, any failure to detect new infections will alter its value. There could be many reasons for this. Some are: targeting screening largely to symptomatic and not identifying the asymptomatically infected, delays in testing and of reporting test results, the use of tests of lower sensitivity and overall insufficient testing."

Professor Mukherjee adds that TPR and R also depend on multiple factors, detecting the proportion of true cases could mean a lot.

"The TPR and R is a function of a multitude of things. It also depends on what fraction of cases you are detecting. Lots of possibilities can happen. There is heterogeneity in the states in terms of the degree of underreporting (or the fraction of true cases you are capturing). That could influence it", said Bhramar.

Professor Menon suggests that we must look at both the values and trends in the test positive ratio.

He said, "One way to assess this is to look at the value of, and trends in, the test positivity ratio. In general, values of the TPR much in excess of 5% (the WHO recommendation), together with an increasing trend in its value, are signals that cases are growing undetected. This implies that testing is insufficient and that the values of R obtained from reported numbers should be trusted less. Maharashtra, Karnataka and Punjab are the most worrying in this respect. It would be interesting to examine the trends in these over the past few weeks."

Professor Mukherjee stresses upon serosurveys that chalk out the details of true infections - crucial in understanding the virus.

"We need a population-based national serosurvey to estimate what percentage of India is truly infected to come up with accurate longer-term projections. The large degree of asymptomaticity or presence of covert infections is the acute reality for India, we know that with roughly 6 million reported cases we probably have 100 million true infections the detected cases are possibly just a proxy marker of more severe symptomatic infections," she said.