TARGET R0<1

Any lockdown targets a reduction in the basic reproduction rate of an infection or to reduce the number of people each confirmed case infects, according to a study published by the Imperial College London Covid-19 Response Team on March 16.

Scientists use a basic reproduction number, R0 or ‘R naught’, to indicate how contagious a disease is. R0 is the number of people who can contract a disease from one infected person. The R0 of Covid-19 remains a matter of research, but a study titled ‘Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus–infected Pneumonia’ published in the New England Journal of Medicine, determined a baseline assumption of R0=2.4.

The larger goal for any government is to keep R0 below one – that is each confirmed case infects fewer than one person.

Here’s what happens with various scenarios.

1: NO CURBS

In this case people are free to move around and interact. Based on R0=2.4, research in Wuhan finds that each infected person will infect 2-3 people on average.

As the first case is reported, the infected person passes it on to a second wave of two or three more people who are also moving without restrictions. The newly infected people again infect the same number of people creating a cycle. This leads to a

3 : LOCKDOWN AND HOME-QUARANTINE

In this case, extensive social distancing is applied throughout the populace by limiting people’s movement through both homequarantines and lockdowns over a period of time.

The aim is to reduce R0, to below 1 and take case numbers to low levels or eliminate humanto-human transmission.

In the Imperial College model, this required social distancing for the entire population, over a long period of time.

“It is likely such measures will need to be in place for many months, perhaps until a vaccine becomes available,” one of the study’s researchers, Neil Ferguson, said in a written statement issued by the college. “The effects on countries and the world will be profound.”

This strategy yields the best results so far as the virus spread ends up being a trickle.

By closely monitoring rise in the infections, governments may be able to lift curbs temporarily, and reinstate them if numbers began to rise.

This is the kind of lockdown India has enforced for three weeks.