Risk of Second Wave at 97 Percent If COVID-19 Lockdowns Lifted 14 Days after No New Cases

Lifting all lockdown restrictions two weeks after no new coronavirus cases are recorded in an outbreak carries a 97 percent risk a second wave emerging, according to a study on the Chinese city, where the COVID-19 pandemic is thought to have started.

In such a situation, the surge would happen 34 days after all controls were lifted, the study found. If some rules were kept in place, the risk would drop to 32 percent, with the rebound hitting in the following 42 days. Xingjie Hao of China's Huazhong University of Science and Technology and colleagues, published their findings in the journal Nature.

The team used data on the Chinese city of Wuhan to create a model exploring the dynamics of the COVID-19 outbreak there between January 1 and March 8. This included information on 32,583 laboratory-confirmed coronavirus cases between December 8, 2019 and March 8, 2020. They broke the time period into five chunks, according to certain events and interventions that affected the spread of disease, like Chinese New Year and community screening programs.

The model also accounted for factors including individuals spreading the virus before they showed symptoms and transmissions rates, and the movement of people.

On January 23, the authorities locked down Wuhan, including stopping travel in and out, social gatherings, and quarantining mild patients at home. By February 2, all residents had to stay at home, and those with the coronavirus and their close contacts were isolated. Between February 17 and 19, workers carried out door-to-door symptom checks.

According to the team, two factors played a role in the COVID-19 becoming a pandemic, asymptomatic spread and how easily the virus could be passed on.

The researchers estimated that 87 percent of the infections in March went undetected. This potentially included people who did not show symptoms or had a mild form of COVID-19.

The study also showed the outbreak could be controlled with approaches for preventing the spread of disease from unknown cases, such as wearing face masks, social distancing, and quarantining close contacts. Interventions likely reduced the total infections in Wuhan by 96 percent as of March 8.

The "drastic interventions [taken by the authorities], together with the improved medical resources and healthcare manpower from all over the country, have effectively crushed the epidemic curve and reduced the attack rate in Wuhan, shedding light on the global efforts to control the COVID-19 outbreak," they wrote.

Since the pandemic started, researchers have carried surveys looking for antibodies to the COVID-19 coronavirus in people's blood. Like this study, they suggest more people have been infected by the coronavirus than case counts suggest, the authors said. Future research, like more antibody surveys, should be conducted to corroborate the findings, according to the team.

The study was limited, they said, because delays in laboratory test results may have meant some cases were missed. Also, people with signs of COVID-19 who did not have a swab tests were excluded to avoid false positives, which could have meant cases were underestimated.

The study comes as the U.S. faces a spike in coronavirus cases, particularly in the West and South. The rise has partly been blamed on officials re-opening economies too quickly.

Co-author Xihong Lin, professor of biostatistics at Harvard T.H. Chan School of Public Health, told Newsweek via email the study suggests that detected cases "are the tip of the iceberg.

"Efforts are needed to detect and isolate asymptomatic and mildly symptomatic cases, such as testing, contact tracing, and isolation and quarantine."

Lin said there are two key messages to take from the study. "Even if we cannot detect all the cases, interventions such as universal mask wearing, social distancing, and avoiding 3Cs (crowded places, close contact settings; confined and enclosed places), can effectively block the transmissions stem from the undetected cases. This is probably how Wuhan was able to suppress the local outbreak.

"Second, to reduce the chance of resurgence, consider reopening when the number of cases is sufficiently small, and ensure control measures continue to be in place and keep up with compliance after reopening. Remain vigilant after reopening, and wear masks."

This article has been updated with comment from Xihong Lin.

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A staff member wearing a face shield gestures at a long-distance bus station in Wuhan in China's central Hubei province on April 30, 2020. STR/AFP via Getty Images