North China’s Tianjin Municipality, home to 15 million people and also a major gateway and “moat” to Beijing, rolled out massive nucleic acid testing on all its residents on Sunday morning after the city detected 20 COVID-19 infections in one day, with two cases found with Omicron variant. 

Epidemiologists said it’s the first real battle against Omicron on the Chinese mainland as Omicron-infected domestically-transmitted cases were discovered in local communities for the first time.  They also warned of a huge uncertainty and high possibility of a spillover as the source of the outbreak remains unknown. But epidemiologists assured the public that as long as timely investigation of the origins is conducted and effective measures are put in place, the outbreak will be staunched before China’s Spring Festival, which is three weeks away. 

Tianjin reported on Sunday two locally transmitted cases with the Omicron variant, which were found among people who volunteered to get tested. Then another 18 cases were found in a follow-up test of high-risk groups. The Tianjin municipal government said the two cases were in the same transmission chain, but are not linked with the imported Omicron case detected in December, 2021 in the city. 

It remains unknown whether the other 18 residents also have the Omicron variant. 

Among the 20 infected people, 15 are children aged between 8 and 13. The cases are concentrated in Tianjin’s Jinnan and Nankai districts. 

To ensure the safety of residents and contain Omicron from further spreading, residents of the city are required to stay put and receive a test. The nucleic acid testing on all residents started on 7:00 am Sunday morning and is expected to complete within 24 hours, according to a notice from the city’s anti-epidemic command center.

As of Saturday night, Tianjin has quarantined 75,680 people. Among 70 environment tests, 14 of were positive and two were detected in elevators of residential buildings.

The health code of people who won’t receive the test within 24 hours will be turned to orange. Residents who have been vaccinated for less than 48 hours will not participate in the test, the command center said. 

The anti-epidemic command center said at an urgent meeting, participated by the city Party chief Li Hongzhong and mayor Liao Guoxun, on Saturday night that the massive testing is a concrete measure to fulfill the responsibility of Tianjin to be a “moat” of Beijing and contain the epidemic at the fastest speed and the lowest cost. 

The test will support the city to have better understanding of the epidemic risk and ensure safety of lives and health of residents, the command center said.

Based on the patients and viral transmission chain, the newly added 18 infections have already spread the virus to three generations of people. Although the outbreak was detected on Saturday midnight, it probably has spread among the community for a certain period of time, Zhang Ying, a deputy director of the municipal health commission, said at a late press conference on Saturday night. 

More positive infections are expected to be found, Zhang said. 

Affected by the epidemic, subway lines one and six will be partially closed starting from Sunday. The Tianjin Binhai International Airport has cancelled 144 flights that were scheduled on the day.

Entry checkpoints from Tianjin to Beijing have heightened epidemic inspections. Commuters are being asked to contact their employers and communities and sign up a letter of commitment before they are allowed to enter Beijing. Many vehicles and people were persuaded to return. Some residents who returned to Beijing from Tianjin in recent days have been asked to quarantine at home.

The inter-city train between Tianjin and Beijing is operating normally as of press time.

The Beijing Center for Disease Control and Prevention on Sunday told people in Beijing not to visit Tianjin and those in Tianjin not to visit the capital. Commuters between Tianjin and Beijing are encouraged to work from home. 

Anyone in Beijing who have visited Tianjin’s Jinnan and Nankai districts since December 23, 2021 will be quarantined at home and tested. Others who have travel history to Tianjin since the same date need to report to their local communities, employers and hotels immediately, the center said.

Fearing a lockdown, several Tianjin residents told the Global Times that people rushed to markets to snap up food. A resident surnamed Liu said that a supermarket near her house was full of people at 7 am on Sunday morning, and the queue was as long as 200 meters.

Another resident surnamed Wang said most vegetables were sold out early on Sunday morning, and the delivery service in nearby market was suspended.

Liu said that although the outbreak came so sudden, she appreciates the local government’s swift response. She added that the overnight nucleic acid testing “assures people.”

The Global Times learned that two biggest universities in Tianjin, Tianjin University and Nankai University, both with branches in Jinnan district, where the most cases were found, have imposed restrictions on leaving and entering of their campuses. Tianjin University notified students on Sunday that it has postponed final examination to next semester. 

A Beijing-based immunologist told the Global Times that it’s the first real battle against Omicron on the Chinese mainland as Omicron-infected domestically-transmitted cases were discovered in local communities for the first time.  

Huge uncertainties exist for the Tianjin outbreak as the source of infection remains unknown. If the Omicron virus has spread to three generations of people in the community, Tianjin’s COVID-19 cases will increase rapidly and reach 100 soon, he said.

The immunologist warned of the risks that the Tianjin outbreak poses to Beijing, because of a large number of commuters working and living in the two cities.

Apart from Tianjin, China has seen sporadic outbreaks in other cities and provinces. 92 locally confirmed COVID-19 cases were reported on Saturday, scattered in places such as Henan Province, the city of Xi’an, Ningbo and Shenzhen.

The coronavirus is more likely to cause an outbreak and infection during winter, that’s why China is seeing more frequent sporadic outbreaks at the moment, Yang Zhanqiu, a deputy director of the pathogen biology department at Wuhan University, told the Global Times.

Yang said that one thing for sure is that it is important to identify the source of an outbreak and time frame of infection as soon as possible. “As soon as the source and time of when the virus arrived in China are identified, larger scale of spillover can be controlled,” he said.

The virologist said that city-wide nucleic acid testing is the quickest way to find cases and prevent further spreading. “The virus has four to five dormant days, number of confirmed cases will keep climbing in the future,” said Yang, noting that it remains unknown how long the virus has been lurking in Tianjin, and it is possible it’s already spilled over to other provinces.

“Now it is only three weeks away from China’s Spring Festival, if we can pinpoint the source and take corresponding measures, the outbreak in Tianjin will be staunched in time,” Yang said.