ATANU BISWAS

While India entered into the “Unlock 1.0” stage from June 1 — in a bid to restore normalcy in a phased manner — it is worth evaluating the evolution of the epidemic in the country since the pre-lockdown stage, which passed through four stages. There is no denying that the economy has to be opened up at some point or the other, in a phased manner. The appropriate timing, however, is a complex decision, based on various parameters of the epidemic and the economy. The most important single parameter of the epidemic is R0 (pronounced Rzero or R-nought), which has become a common term during the epidemic.

It is the “basic reproduction number”, which represents the magnitude of the epidemic. It is the average (or expected) number of secondary infections generated by an infected person during one’s entire infectious period. If R0 is greater than one, one infected person will infect more than one, on average, and the outbreak will lead to an epidemic. R0 less than one implies that one infected individual will infect less than one, and thus the outbreak will eventually become extinct. When R0 is 1, one infected person will infect exactly one person, and thus the number of those infected would remain constant over time.

And (R0 -1)/R0, the “herd immunity threshold”, is the proportion of individuals needed to be infected to achieve herd immunity.

The higher R0 is, the greater the number of people that will need to be infected before herd immunity is achieved. Thus, it is desirable to bring down R0 as much as possible, and that was the main objective of the prolonged lockdown.

We use data on the pre-lockdown period (March 14-24), followed by lockdown 1.0 (March 25-April 14), lockdown 2.0 (April 15-May 3), lockdown 3.0 (May 4-18), and lockdown 4.0 (May 19-31), to obtain the R0 values, assuming a suitable common generating time distribution across the country. For India as a whole, the pre-lockdown R0 value during March 14-24 was 3.30. Thus, one infected was infecting nearly another three and one-third, on average, at that stage. During the four stages of the lockdown, the successive R0 values were 1.57, 1.40, 1.38 and 1.44. Thus, the epidemic slowed down as soon as the lockdown was imposed. However, R0 didn’t dip below 1, implying that the epidemic was not declining. It remained almost stable despite more and more relaxations. That may encourage more relaxation, eventually “unlocking” the economy through phases.

However, such estimates of R0 are subject to error, due to the difficulty in

R0 values, or the average number of infections expected to be caused by a Covid carrier, vary between states, and have not stabilised. While unlocking, it would be wise to look at these variations