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

this case, a region with a high number of cases is locked down -as in China’s Hubei .

In a study titled ‘The effect of travel restrictions on the spread of the 2019 novel coronavirus (COVID-19) outbreak’ published in the journal Science by a group of American, Italian and Chinese researchers on March 6, scientists found that travel restrictions in Wuhan slowed the spread. While the model output showed no noticeable differences in the epidemic in Wuhan, it showed a delay of about three days for other locations in China.

This strategy focuses on slowing down, not necessarily suppressing the epidemic. This flattens the curve slightly, buying time to strengthen health care facilities. It also means a reduction in peak health care demand, freeing up hospital beds and protecting those most at risk.

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.

In this case each dot is a person who is free to move around and interact with other people. Based on R0= 2.4, we can assume that each infected person will infect 2 to 3 people on average

HOME QUARANTINE

In this scenario extensive social distancing is applied throughout the populace by limiting people’s movement through both home-based quarantines and lockdowns

Uninfected person

In this phase, as the first person gets infected, they pass it on to a second wave of two or three more people. These newly infected people are also moving freely without any curbs in place to prevent them from infecting others

In this phase, once an outbreak flares in a region, we create a brief lockdown over a city or region to contain the spread of the disease there. This generally leads to a high concentration of cases in the area, but contains the virus there

Much like the other phases, we will assume that the first person ended up infecting a first wave of two or three people. Among the three people infected here, two are enforcing social distancing measures or are limited by the area-wise lockdown, so only one forms the chain of infections

Since there are no restrictions on the movement of anyone here, the newly infected people are likely to pass on the infection to the same number of people (two to three) again. This ends up starting a chain of exponential increase in new cases

Large-scale quarantine zones, however, are very hard to enforce for long periods of time. Once open, or when some cases leak out of the quarantine zone, the virus breaks out to the larger populace, albeit at a slower rate than in a case with no curbs