The 11-week coronavirus lockdown in Wuhan, China, ended Wednesday, allowing residents to leave their homes for periods of time with clearance from a government-sanctioned app.
Shops are beginning to open again, and people are leaving the city en masse. Schools remain closed, and residents are still encouraged to stay home as much as possible, but some people are beginning to congregate in the streets for conversation or games.
Since Wuhan's shutdown began January 23, China has seen a drop-off in its rate of new cases. The country reported no new local infections for the first time March 19. Outside Wuhan, authorities have gradually lifted restrictions over the past two weeks.
Italy imposed similar lockdown measures in March, and many other countries have followed suit. But some experts fear that lifting those restrictions could enable the virus to start spreading all over again.
Lockdowns merely delay an outbreak's peak by about three months, Dr. Ben Cowling, an epidemiologist at the University of Hong Kong who researches influenza transmission and control measures, told Business Insider last month.
"What happened in Wuhan and now what's happened in north Italy is not the peak of an epidemic. That's about a month away from the peak," he said. "They are still facing now, most likely, a second wave in one to two months' time. So are they going to shut down again?"
Travelers and asymptomatic people spread new waves of infection
There are two main ways the virus can make a resurgence as residents emerge from their homes, return to work, take their children to school, and go shopping.
First, a small number of residents who were under lockdown could still have the virus when restrictions lift but not know they're sick. Those people could then spread it, starting a new wave of infections.
Second, international travelers could bring the virus back into the country.
The latter seems to have sparked a surge of new infections in Hong Kong.
Hong Kong's outbreak consisted of just 100 cases at the beginning of March; the city had implemented widespread social distancing, work-from-home rules, public-information campaigns, and high-tech case mapping. On March 2, civil servants went back to their offices. Two weeks later, the city reported a jump to 160 COVID-19 cases.
As residents who had been abroad began returning home, Hong Kong's cases more than doubled. At the end of March, it had reported more than 400 cases of the new coronavirus. As of Wednesday, the city had reached 960 infections.
"This is a pattern playing out across parts of Asia — mainland China, Singapore, Taiwan — that were among the first to tackle the outbreak," the CNN analyst James Griffith wrote on March 23. "All are now introducing new restrictions as a sudden wave of renewed cases begins to crest."
Hong Kong's chief executive, Carrie Lam, said the city had already weathered its first two waves of the virus.
"The first wave was the worries of transmissions from mainland (China), so we have put in a lot of measures," Lam said as the city announced new restrictions, according to CNN. "The second wave was the local transmissions, with those clusters arising from dinners and other things. Now we are facing the third wave."
In late March, Hong Kong sent civil servants back home and implemented testing requirements for anyone entering the city. Lam also requested that bars and restaurants stop selling alcohol. On Wednesday, Hong Kong extended all of its restrictions an additional two weeks, to April 23.
Hong Kong, mainland China, Singapore, and Taiwan have all barred nonresidents from entering.
New waves could lead to multiple shutdowns
Almost all new coronavirus cases in mainland China are now coming from people traveling from abroad, including Chinese students returning home.
"Those are now seeding the second wave," Cowling said. "They need to decide whether to do another shutdown."
Along with barring foreigners from entering, some jurisdictions in China have already reimposed business closings shortly after lifting them.
Preventing the importation of new cases will be key to containing the next wave. A study published in the journal Science found that travel restrictions could be effective once a country or territory had controlled the virus' spread within its own communities.
"Chinese provinces and other countries that have successfully halted internal transmission of COVID-19 need to consider carefully how they will manage reinstating travel and mobility to avoid the reintroduction and spread of the disease in their populations," Moritz Kraemer, a lead author on the study, said in a statement.
Chinese scientists and health experts had previously downplayed the threat of another domestic wave of coronavirus infections, however.
"For me, a second outbreak (of coronavirus), a domestic outbreak in China, wouldn't be a great concern," Cao Wei, the deputy director of the Department of Infectious Diseases at the Peking Union Medical College Hospital, told Reuters on March 18.
But experts have pointed out that the 1918 flu pandemic killed more than 50 million people in three waves. The second was the deadliest.
Once COVID-19 cases begin to rise again in any area, authorities would most likely have to mandate social distancing again — a second lockdown.
"What happened in Wuhan could happen repeatedly to a city," Cowling said.
Holly Secon and Bill Bostock contributed reporting.
