Did Tianjin’s Omicron coronavirus outbreak start elsewhere in China? Health officials investigate

·5-min read

Genome sequencing has shown that an ongoing Omicron coronavirus outbreak in Tianjin has a different source to earlier imported cases, according to a senior official at the northern Chinese city’s centre for disease control and prevention (CDC).

Zhang Ying, deputy director of the Tianjin CDC, told state broadcaster China Central Television (CCTV) on Monday night the Omicron strain circulating in the city might have come from another part of China or was transmitted through imported goods or other environmental contamination sources.

Zhang said the strain now in the city did not share the same source as the earlier imported cases in Tianjin.

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Tianjin has tested almost 12 million people since Sunday morning, detecting 77 new positive cases among the results for nearly 7.9 million people so far.

That pushed the total number of positive cases in the city’s Omicron outbreak to 97, 90 of them from Jinnan district. Of those, 49 were symptomatic cases and 15 asymptomatic. Another 33 tested positive and are awaiting confirmation.

In Tianjin, schools are the hotbed of infections and all classes in Jinnan district have been suspended.

Top epidemiologist Li Lanjuan called for efforts to speed up the vaccination of young children. China has been vaccinating children over the age of three.

According to China CDC Weekly online publication on December 13, a 35-year-old man and a 17-year old student flying from Warsaw, Poland, to Tianjin were found carrying the highly transmissible Omicron strain.

But Zhang said there might be another source for the current outbreak.

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“We cannot directly rule out that the virus is imported directly, because the spread of virus is not only through humans, but it can be spread via objects or environmental [contamination]. We are still investigating other possibilities for the virus to be imported to Tianjin directly,” she said.

“There is another option – would it be possible that it is not imported but came from other areas [in the country] and spread to Tianjin? We are tracing this simultaneously and we have found some clues already.”

Chinese scientists have suggested previously that cold chain or other contaminated imported goods could be a source of infection, although most overseas scientists say the chance of that method of transmission is very slim.

Han Jinyan, deputy director of Tianjin’s health commission, said the age of cases in the city ranged from 5 to 74. The first case showed symptoms on December 29. Clusters emerged from January 6 and the virus spread at events such as funerals and venues like schools.

Among the patients, three people had had one shot of a vaccine, 76 had received two doses and 20 had received boosters.

All but one of the children confirmed with the virus were vaccinated.

Han said community transmission was going undetected in the city.

Zhang said the Omicron strain – which has a shorter incubation period than its predecessors – might have been “hiding” in the city for some time.

An Omicron infection could spread from one person to the next just 2-3 days after the first person was infected, making it possible for three generations of the virus to spread in 15-20 days. Zhang said it was difficult to trace the origin because many carriers were asymptomatic or had mild symptoms.

On Sunday, the city of Anyang in central Henan province uncovered two Omicron cases that could be traced to a university student from Tianjin, but it was discovered nearly two weeks after the strain had spread to the inland city.

Zhang said the two Omicron cases in Anyang were asymptomatic, making it difficult to trace their origins.

From 12am on Monday morning to 8am on Tuesday, 58 new cases were reported in Anyang. Although officials have not yet said if they are Omicron cases, local media has reported that some local contacts of the confirmed cases tested positive to Omicron.

All residents of Anyang, with a population of 5.2 million, are barred from leaving their homes except to go out for a swab test.

Tianjin is under enormous pressure to ensure its Omicron outbreak does not spread to neighbouring Beijing, which will host the Winter Olympics in about three weeks.

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Zhang said she was in contact with her Beijing counterparts every morning to share information about how to stop the Omicron outbreak spilling over to Beijing. Two towns in Jinnan district, where the outbreak was most serious, were sealed off.

Tianjin has tested 9.6 million people in three days and received test results for 3.4 million people. Zhang said all positive cases so far were from Jinnan district, although she said it was possible cases might later be found in other areas.

By Monday 6pm, 31 symptomatic cases and 10 asymptomatic cases were reported in Tianjin.

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