As of Wednesday March 25, over three billion people around the world are undergoing a degree of home lockdown and social distancing. Nearly 70 countries have introduced some kind of home confinement measure, from mandatory lockdowns enforced by police or military, to milder isolation recommendations and curfews.

India, the second most populous country in the world, has introduced incredible sweeping measures to contain the spread of coronavirus. For 21 days the country’s entire population of 1.3 billion will be banned from leaving their homes.

The use of the word unprecedented has been pervasive over the past few weeks, but unlike many recent trends where words are hyperbolically misused ("literally", I’m looking at you), the word is profoundly apt. What is happening right now is absolutely without precedent.

We can look to past viral pandemics from over a century ago to find some kind of parallel, however, the nature of a massive globalized population makes negotiating a viral pandemic in the 21st century an entirely unique proposition.

While confining billions of people to their homes may effectively stifle the acute spread of this new virus, some massive questions are now being asked: How long will people have to stay in their homes and physically isolate? Weeks? Months? A year? And will the pandemic spike again when we try to return to normal?

Shutting a city down, China-style

On January 23, China began a mass quarantine, the scale of which the world had never seen. Wuhan, the epicenter of the viral outbreak, and home to over 11 million people, was locked down. Transport in and out of the city was stopped. Residents were initially barred from leaving their homes for any reason other than to acquire food or medicine.

Some areas were more stringent than others but as the days passed, isolation measures generally became more aggressive. Food delivery drivers kept the city alive as officials began to conduct door-to-door health checks, isolating anyone with signs of the virus.

Across China lockdown policies varied, with the most extreme measures directed at around 57 million people in the province of Hubei. At its peak, over 500 million people in China were affected by some kind of restriction policy.

And it may have worked … for now.

On March 19, China reported zero new domestic COVID-19 cases. A small volume of cases were still appearing, but these seemed to be linked to travelers returning from outside of the country.

Now what?

After two months of extraordinary restrictions China is very slowly lifting its lockdown. Areas in Hubei province that haven’t recorded new cases for over two weeks have already begun easing isolation and travel restrictions. If no new local infection spikes appear, the city of Wuhan will begin to lift traffic restrictions from April 8.

A leading infectious disease modeling team based at Imperial College London is now suggesting China’s extreme social distancing measures have been successful in containing the virus. And, there are very early indications the initial phases of relaxing those strict measures have not rekindled local viral spread.

So far, at least.

“By investigating the relationship between within-city movement and the estimated reproduction number, we observed that the relaxation of strict social distancing measures and resumption of economic activities, so far, has not resulted in frequent local transmission of COVID-19 in China,” says Han Fu, co-author on the latest Imperial College London report.

China’s deeply comprehensive social surveillance systems cannot be easily translated to other places.

Steven Riley, another co-author on the new Imperial College report, confirms the new analysis’ conclusion, that at least as of right now, China is proving that relaxing extreme social distancing measures does not immediately lead to viral transmission returning.

“Although we do not know what will happen next in China, this report shows that very stringent social distancing can be relaxed after containment has been achieved without transmission returning in the short term,” says Riley.

The big question the rest of the world now faces, as billions isolate to suppress viral spread, is what can we learn from China? Unfortunately, China’s deeply comprehensive social surveillance systems cannot be easily translated to other places.

Take, for example, its new color-code system for regulating citizen movements.

The system launched in early February in Hangzhou, assigning all residents either green, yellow or red QR codes via a smartphone app. A green QR code means a resident is free to travel and move about a city. A yellow or red designation, on the other hand, means one has to report to authorities immediately and enter quarantine.

Authorities are scanning QR codes as people move about, from entering subways to shopping malls, every resident can expect to continually be asked to present their phone for scanning. But how does the system determine its color-coded designations?

No one is entirely clear exactly how the app is making its decisions. Chinese authorities are unsurprisingly not entirely transparent regarding what can turn a person’s status from green to yellow or red. It is suspected data including a person’s movements, duration spent in known areas with infections, and contact with potential carriers are all evaluated by some kind of automated algorithm, with a person's color code updated at midnight every night.

How long will the lockdowns need to last?

The first question many governments around the world are grappling with is how long will extreme social distancing measures need to be initially in place?

China may have managed to curtail the spread through extraordinarily extreme measures, lasting around eight to 10 weeks. Whether other countries around the world have the ability, or will, to impose such stringent measures is yet to be seen.

A new University of Sydney study modeled the spread of COVID-19 across Australia and quantified the direct relationship between the duration of these acute social distancing measures and the percentage of the population that abides by the rules.

"If we want to control the spread of COVID-19 – rather than letting the disease control us – at least 80 percent of the Australian population must comply with strict social distancing measures for at least four months," explains study lead on the new modeling, Mikhail Prokopenko. "However, if 90 percent of the population complies, then the duration could be as short as 13 to 14 weeks – meaning if we began tomorrow we could expect a control of COVID-19 by July.”

Perhaps the most striking finding in the study is the revelation that if less than 70 percent of the population comply with social distancing practices, the pandemic cannot be suppressed. Prokopenko suggests any social distancing practices would be “fruitless” if not adopted by a large enough volume of people.

Mark Lipsitch, a professor of epidemiology from Harvard University, is reticent to put an exact date on how long initial strong social distancing needs to last. He suggests China may have successfully got on top of the spread after eight weeks but its measures were extreme, and it started them before its health care system became significantly stressed.

“… in other cities in China where it never got close to crashing the health care system, you can do a lot of good in six to eight weeks of social distancing,” Lipsitch said in a recent press conference. “The question is now, if you start social distancing when you see your health care system crashing, as has happened in Italy and I fear is going to be the case in many parts of the United States that don’t seem to be getting with the program yet, then that means that you have more cases in the population and that it will take longer to get down to close to zero.”

In the wake of a recent tweet from President Donald Trump suggesting social distancing measures in the United States should begin relaxing as soon as mid-April, a chorus of health experts around the country warned this would be much too soon. Tom Inglesby, an epidemic expert and director of the Johns Hopkins Center for Health Security, presented a disturbing picture of what could happen in the United States if social distancing measures were prematurely relaxed.

“Anyone advising the end of social distancing now, needs to fully understand what the country will look like if we do that,” Inglesby wrote in an expansive Twitter thread. “COVID would spread widely, rapidly, terribly, could kill potentially millions in the year ahead with huge social and economic impact across the country.”

Inglesby notes there is at least a three-week lag between commencing social distancing measures, and seeing results in transmission data. He points to the Wuhan timeline as good evidence of a transmission curve taking several weeks to respond to massive social distancing measures.

These big social distancing measures take time to work. The impact of big interventions in Wuhan China took about 3 wks to start to reverse things. And then everyday after the situation got better. In the US, we're about 7 to 10 days into this, depending on the state.10/x — Tom Inglesby (@T_Inglesby) March 23, 2020

So it seems increasingly clear that extreme social distancing measures will need to be in place for anywhere from one to three months, at a minimum, to suppress the initial wave of infections.

But what happens after that? How can the virus be contained for the stretch of time it will take scientists to develop a vaccine and/or enough people contract the virus to establish a minimum of herd immunity?

The second phase

What this second phase will look like is a big mystery right now, and every government around the world will most likely approach things differently. Even if China manages to suppress a second spike over the coming months, no other country in the world has the means to replicate its profoundly comprehensive surveillance methods.

Juliette Kayyem, a former senior Homeland Security official, suggests if we can pass this first strong phase of social distancing and corral the spread, the world will still look very different as longer-term state suppression efforts will commence.

“At that stage, then we'd be able to isolate the sick, test their contacts, care for them in available intensive care beds with available respirators because we've surged resources,” Kayyem recently told NPR. “It will look and feel different. I mean, there will – it won't feel normal because there will be outbreaks here and there, and the lights don't go on immediately – but we will begin to get, you know, essentially what's a steady-state suppression effort until we get a vaccine distributed.”

The unsettling message, echoed by many experts, is that much of the real work begins only once this acute viral peak is suppressed. For the second half of 2020, mass testing and contact tracing will be necessary to catch and isolate new cases as they appear, stopping localized outbreaks from spreading.

“We will need system of screening at airports so that no person comes into the country with the disease without being diagnosed and isolated,” explains Tom Inglesby, discussing how this second phase needs to play out. “We'll need a serology test that can be used to identify those that have been infected and recovered already, and to know how prevalent disease is in the US. We would hopefully have therapies developed and in a quantity that we can treat at least the sickest patients with COVID. Once we have those things in place, it would be a far less risky time to take stock of social distancing measures in place and consider what might gradually be reduced with trial and error. We would have learned more about the experience in Asia as they try to do that.”

An influential model from Imperial College London last week revealed active social distancing measures may need to be intermittently turned off and on over the next 18 months until a vaccine is developed and mass immunity occurs. A more recent model, produced by Mark Lipsitch and his team from the Harvard T.H. Chan School of Public Health and focusing more specifically on the United States, came to a similar conclusion.

... the overall duration of the SARS-CoV-2 epidemic could last into 2022

That model confirms if an acute phase of social distancing is not followed up with comprehensive surveillance, oversight and interventions, then the peak of the epidemic in the United States will simply be pushed back to autumn. The study warns pushing the epidemic peak into wintertime may ultimately exacerbate transmissibility as it is still unclear whether the virus spreads faster in cooler seasons.

One of the worst-case scenarios presented in the new Harvard model is the epidemic stretching into 2022. This scenario is based on current levels of critical care services in the United States.

“The length of time between distancing measures increases as the epidemic continues, as the accumulation of immunity in the population slows the resurgence of infection,” the study suggests. “Under current critical care capacities, however, the overall duration of the SARS-CoV-2 epidemic could last into 2022, requiring distancing measures to be in place between 25% (for wintertime R0 = 2 and seasonality) and 70% (for wintertime R0 = 2.5 and no seasonality) of that time.”

The ultimate conclusions are not exactly comforting, but the study does note that a huge number of variables could offer more positive outcomes. This model does not take into account the development of new treatments, novel methods of tracing and testing, or even the unlikely possibility of the virus naturally waning.

“New therapeutics, vaccines, or other interventions such as aggressive contact tracing and quarantine – impractical now in many places but more practical once case numbers have been reduced and testing scaled up – could alleviate the need for stringent social distancing to maintain control of the epidemic,” the study concludes.

The long haul

So when will all this be over? When will you be able to comfortably leave your house and return to some kind of normal activities?

Unfortunately there is no simple reassuring answer to that question, and although this will end at some point in the future, that point may still be at least 12 to 18 months away. In his latest media briefing, WHO Director General Tedros reiterated a message he is broadly trying to communicate to many countries right now – these initial lockdown measures are about buying time to establish broader systems of control and ease pressure on healthcare agencies.

“… on their own, these measures will not extinguish epidemics,” says Director General Tedros. “The point of these actions is to enable the more precise and targeted measures that are needed to stop transmission and save lives. We call on all countries who have introduced so-called lockdown measures to use this time to attack the virus. You have created a second window of opportunity. The question is, how will you use it?”