In the last two weeks of 2020, China has seen a sharp increase in Covid-19 infections, with clusters in three very large cities. The spread of the virus, despite China’s relatively strict testing, quarantine, and contact tracing measures, is a serious warning of how dangerous and highly infectious this coronavirus is.

In December, according to the National Health Commission of China, 122 cases of Covid-19 infections have been recorded, a 107 percent increase from the 59 cases in November. Among the 122 cases in December, more than two thirds occurred in the last two weeks of the month.

These infections took place in three major cities: 24 cases in Beijing, 17 cases in Shenyang, and 43 cases in Dalian. Both Shenyang and Dalian are located in Liaoning Province in northeastern China—the former is its capital and the latter its major port city.

It is particularly disturbing that China has had three almost simultaneous but separate clusters of outbreaks, something that has not been seen in the past few months. As the weather gets colder with ventilation more limited, and as the Lunar New Year approaches where hundreds of millions will travel back to their hometowns, infections could escalate and spread much more widely.

An examination of the chain of infections in these three cities further underscores the highly contagious nature of the COVID-19 virus. It not only poses a huge challenge to China in keeping the infection rate relatively low as in the past months, but could pose further dangers for countries like the United States and Britain where the virus is basically spreading freely under the murderous “herd-immunity” policy.

Beijing

The infections in Beijing all originated from a common source. On November 26, a 28-year-old man flew into China from Indonesia. Another passenger on the same flight tested positive on arrival, but the young man tested negative. He was quarantined for 14 days in Fujian Province, where he entered China. After he tested negative, he left for Beijing where he lived. A month later, on December 26, his nucleic acid test still yielded negative results, but his IgM antibody test showed positive results, indicating he had already been infected. He was then hospitalized, and only two days later, on December 28, his nucleic acid result turned positive as well. After a whole-genome sequencing of the virus, it was determined that the virus most likely came from Southeast Asia, from where he had traveled.

His flat mate was also infected and passed the virus to a staff member at a local supermarket. Then, the staff member infected her husband, her co-workers, a cab driver, and two friends who she went out with. Both of her friends then infected their husbands. Four of the infected people were working at an industrial complex in the suburbs of Beijing and transmitted the virus to five other co-workers. Since December 25, a lockdown was imposed over this industrial complex. The 2,340 people kept inside were tested overnight, and all tested negative. A second round of testing was performed on December 30, and a third round has been planned.

Shenyang

The cluster of infections in the city of Shenyang also started with a person who had traveled internationally: a 67-year-old woman who returned from South Korea on November 29. She was quarantined in Shenyang after her flight and underwent two nucleic acid tests and one antibody test during her quarantine. All results were negative, but she later tested positive on December 23.

During the interim, the woman transmitted the virus to her husband, granddaughter, and a few neighbors. She visited a clinic on December 18. Even though she wore a face mask throughout the entire visit, a nurse and a physical assistant still tested positive later on December 28.

Some 706 people were identified as close contacts, and another 1,833 people were identified as secondary close contacts. They were all tested and collectively quarantined. Another 3,716 close contacts of secondary contacts were tested and quarantined at home. Residents, staff members and students in five neighborhoods, five health clinics and three schools where cases were found, roughly 20,000 people, were tested by December 28, five days after the initial case was detected.

Dalian

The city of Dalian recorded the highest number of cases in the last two weeks of December, 43 symptomatic cases on top of another 36 asymptomatic ones.

As a major Chinese port city, Dalian has a vast industry dealing with imported goods, including a large number of cold-stored products. The initial infections in Dalian were found among porters at a company that handles such goods. Four workers tested positive during a regular screening ordered by the company on December 15, but all of them were asymptomatic. Then, through the screening of their close contacts, more cases were detected each day. People in contact with the virus were concentrated in the district where this cold-storage company operated, including street vendors, small-shop owners, restaurant workers and service workers. The exact chain of transmission has not been completely identified.

Since December 22, an effort was made to test everyone in the city. Now, more than 6 million people have been tested across the city. According to People’s Daily, instructions were issued to vaccinate all workers handling frozen goods by the end of 2020 and to put them in soft quarantine. These workers would only be allowed to leave their workplace area if they had two recent negative test results. A weekly screening with nucleic acid tests among these workers was also planned.

The very detailed contact tracing provided by public health organizations points to multiple health and political issues bound up with the COVID-19 pandemic.

First, people who contracted the virus in this wave of infections are overwhelmingly working class. As is the case in the mass infections in factories, meat-packing plants, schools and Amazon supercenters in many other countries, workers have been put on the frontline of the pandemic.

The cases published by health organizations in China point to the difficult living and working conditions of these workers. For example, one worker at the industrial complex in Beijing who contracted the virus also worked part-time at a transit center for SF Express, the leading package-delivery company in China. On top of a regular workday at the industrial complex, he also worked from 10 p.m. to 2 a.m. at the transit center every day.

Second, the COVID-19 virus is highly infectious. Even though China has been able to keep the number of cases relatively low by carrying out large-scale testing and detailed contact tracing after an infection was identified, the spread of the virus could still not be halted and is potentially escalating.

The cases that initiated the clusters of outbreaks in Beijing and Shenyang, were both properly quarantined for 14 days after international travel and tested negative several times but the virus was still transmitted to their close contacts.

The cases in Dalian were not the first to be infected by the coronavirus carried on the surface of frozen goods. In November, a number of port workers in Tianjin, another port city in northeastern China, were infected by imported frozen pork from North America. A truck driver, who did not handle the frozen goods, was infected by helping porters pick up a bag of frozen meat which carried the virus on the outer package.

Moreover, a report released on December 31 by the Municipal Health Commission in Chengdu, a city in southwestern China where a cluster of infections were reported in early December, found the first case was very likely infected by picking up trash. The trash was thrown out from a quarantine center housing five people who had travelled back from Nepal.

What all these clusters powerfully demonstrate is that the pandemic is fundamentally a global issue that could not be resolved on a national level. It is extremely difficult, if not impossible, for any country to prevent the virus from entering its borders.

All countries are part of globalized production chains, and as long as the pandemic is still raging and killing tens of thousands of people around the world, no country is a safe, virus-free bubble.