China Enters The Next Phase of Its COVID-19 Outbreak: Suppression

There are now so few coronavirus cases in China that some days, authorities don't see any local transmission. China has gone from reporting thousands of cases a day in February to reporting one or two a day now. Over the past week, officials with China's National Health Commission reported just five new domestic cases. The total of new cases was higher, but almost all of them were imported cases in travelers who had recently returned from abroad.

China has driven coronavirus transmission down to nearly zero. (Although there's some question among international academics about China's case reporting and whether some cases are being overlooked, it's generally agreed that the nation has suppressed transmission to a very low level.) But some undetected cases are still probably floating around, and the virus can always be brought back in from abroad.

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So life has not yet returned to normal. Many restrictions from the health crisis are still in place. Isolation wards are still open for patients even with mild symptoms. Quarantine centers are housing suspected patients and contacts of confirmed patients. Testing labs are still running. And monitoring systems are still on high alert for new cases.

"We are very aware that there could still be a second wave in China. That is possible," says Kylie Ainslie, a research associate at the MRC Center for Global Infectious Disease Analysis at Imperial College London.

"However, we haven't seen that occurring yet."

Ainslie and her colleagues have been looking at how China is emerging from one of the largest lockdowns in human history. They've been analyzing GPS tracking data of human movement to monitor how social restrictions are being eased or tightened in any given area.

"Areas where the outbreak was less had movement restrictions removed sooner," she says. "But that didn't mean completely. It meant first they started major factories and started letting those people who work there go back to work so that they could restart their industries."

Movement restrictions — basically orders for people to stay home — are still in place for some areas, and some people are still considered to be high risk.

Most factories in Wuhan, which was the epicenter of the outbreak, for instance, have not yet cranked up their production lines.

"One of the things that China is doing is while it is relaxing social distancing measures, it's not removing them entirely," Ainslie says. "And it's not removing them haphazardly."

For instance, schools in much of the country remain closed.

In several provinces where reported cases have gotten down to zero or close to zero for some period of time, case numbers have rebounded. But those upticks have primarily been driven by travelers arriving from Europe.

Ben Cowling, an epidemiologist at the University of Hong Kong, says these "imported" cases are much easier to contain and don't pose as much of a threat of wider transmission.

"There's less opportunity for infections to get into the general community from those travelers because they are being monitored so carefully," Cowling says. Anyone arriving in China must go into 14 days of quarantine where officials can keep a close eye on their health. "So if they do turn out to be infected, which is a small minority, then they're isolated. Their contacts are traced and put into quarantine. And that's going to slow down any any leakage into the general community."

Cowling says public health officials in China and elsewhere have two sets of tools to contain its outbreak — social distancing and case management. Social distancing makes it harder for the virus to find new people to infect. Case management tracks down cases and potential cases individually and then isolates them – and the virus. China wielded both of these tools aggressively.

"With a lot of testing capacity, they were able to bring down the numbers of infections quickly," Cowling says. "I think more quickly than we will find case numbers decline in New York or northern Italy or Spain or France. And that's because in China, the lockdown was a more extreme version of a lockdown. It was a total lockdown."

People were ordered to stay in their homes and were forbidden from traveling.

"In addition to the lockdown, there was also heavy use of testing, isolation and quarantine," Cowling says. "So all of those measures are like really, really trying very hard to get the numbers down."

China is now in a "suppression" phase of the epidemic. They've gotten transmission down to nearly zero, but some undetected cases are still probably floating around, and the virus can always be brought back in from abroad.

To make sure that another major outbreak doesn't occur, China is experimenting to see how much it can ease off the highly restrictive social distancing while keeping its testing and quarantine apparatus up and running.

"We're going to see within a month or two whether it's possible to get back to relatively normal social mixing and just be able to rely on testing, tracking, isolating, quarantine" to keep the virus at an extremely low level in China, he says.

European countries and the U.S. hope to soon address the challenge of figuring out how to relax social distancing without allowing the virus to come roaring back. But the U.S. may have a harder time doing this than China is. Cowling says one problem facing the U.S. is that there are many different outbreaks that are being managed primarily at the state level and might peak at different times.

"It's possible that New York could be coming out of lockdown, having got the numbers to a low level. But there are other cities where they're having a lot more infections, and it is going to be very difficult to have travel restrictions," Cowling says. "And the worst-case scenario is that infections are kind of bouncing around the U.S. And so, the lockdown is relaxed and then infections come back and then you have to lockdown again and nobody wants that to happen. So it really is a urgent question to figure out what's the best way to suppress transmission across the whole of the U.S."

Watching how China navigates this suppression phase may offer guidance to the U.S. and the rest of the world.