Taking into account the rapid spread of COVID-19, Prime Minister Narendra Modi announced a 21-day country-wide lockdown on March 24. But why has the very specific period of 21 days been chosen?

This has to do with the way the virus behaves – its incubation period, and how it spreads.

“All viruses have a specific incubation period. This particular strain of the coronavirus has a longer incubation period than previously known viruses from the coronavirus family,” explains Dr Padma Srikanth, a microbiologist from Chennai’s Sri Ramachandra Hospital.

She explains that the virus is capable of shedding (being present) in an infected person’s bodily secretions (such as mucus and saliva) of an infected individual for up to two weeks after the person is infected. The lockdown has been enforced for another seven days as a cautionary measure for the individual to fully recover.

Taking this time period into account, epidemiologists across the world have identified a three-week minimum time for people to avoid contact with others – which is why the 21-day lockdown has been enforced.

“This virus has only jumped the species barrier and has begun to infect humans, but it has certain characteristics which have resulted from natural mutations that allow it to easily bind to the surface of human cells. This, plus the fact that it is capable of shedding for up to three weeks makes it very contagious,” explains Dr Padma explains.

Further, with India’s large population density, there is a greater risk of rapid transmission if stringent measures are not taken. Imposing a lockdown ensures that there are less individuals in public areas, and that social distancing is practiced.

Additionally, quarantine and isolation of individuals confirmed as well as suspected to have COVID-19 during this time also aids in containing the spread of the virus.

“Recent research has shown that containment and mitigation measures are the best ways to reduce the spread of the virus,” Dr Padma says.

Will the virus be gone after lockdown?

While the science behind the 21-day period is clear now, the lockdown itself is not enough to stop the transmission completely.

In an interview to TNM, Bhramar Mukherjee, a professor of biostatistics and epidemiology at the University of Michigan and a co-author of the study‘Predictions and role of interventions for COVID-19 outbreak in India’, told TNM that the lockdown is not a “magic potion”, and it will just buy healthcare workers time to deal with what’s to come.

“The virus is not going to disappear. This just buys us time so that we can prepare our army to go on a war. The war is still on, and we should use this time and operate as if on war-footing. Expand testing capabilities, set up a nationwide task force for contact tracing, set up COVID-19 care centers, produce and acquire protective equipment for front-line health care workers,” Mukherjee had said.

Apart from stressing on the need for aggressive testing, she also said that practicing social distancing, banning large gatherings and good hand hygiene are crucial even after the lockdown as well. Read the full interview here.

It is also important to remember that not all infected individuals are symptomatic, even those who may not feel sick or show symptoms could still be carriers of the virus, and can pass it on to another person.

Testing and isolation should go together

The World Health Organisation (WHO) has emphasised that testing and isolation should be done simultaneously for it to be the best way to combat and curb the spread of the novel coronavirus called SARS-CoV-2 which causes COVID-19.

Director General of the WHO, Dr Tedros Adhanom Ghebreyesus, has stressed the importance of testing measures along with practicing social distancing and hand hygiene, as the best way to fight the infection.

“If you look at the measures taken by countries like South Korea, there were strict quarantine and isolation rules implemented immediately and testing was increased, this helped them prevent further transmission of the virus,” explains Dr Padma.