UEA study shows Chinese asymptomatic Covid-19 cases were not infectious

A medical worker records down a patient's condition at Jinyintan Hospital designated for new coronav

A medical worker records down a patient's condition at Jinyintan Hospital designated for new coronavirus infected patients, in Wuhan in central China's Hubei province. Photo: Chinatopix via AP - Credit: AP

Researchers from Norwich have found a mass screening programme of more than 10 million people in the Chinese city of Wuhan identified 300 asymptomatic Covid-19 cases - but none were infectious.

But the University of East Anglia scientists stressed the findings do not show people who have coronavirus, but no symptoms, cannot pass on the virus.

Mass testing took place over two weeks at the end of May – after the city’s stringent lockdown was lifted in April.

The study found no ‘viable’ virus in the asymptomatic cases and their close contacts did not test positive.

Prof Fujian Song, from UEA’s Norwich Medical School, said: “The virus cultures indicated no viable virus in the identified asymptomatic cases. This means that these people were not likely to infect anyone else.”


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The study was led by researchers at the Huazhong University of Science and Technology , in collaboration with UEA researchers.

Asymptomatic cases were found among people aged between 10 and 89,  with the asymptomatic positive rate lowest in children and teens under 17 and highest among people over 60.

Testing of 1,174 close contacts of the 300 asymptomatic positive cases were all negative.

Prof Song said: “This work confirms transmission of Covid-19 can be successfully controlled by well implemented non-pharmaceutical interventions, including face covering, hand hygiene, safe social distancing, contract tracing, and lockdown restrictions."

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However, the research team says it is important the results are correctly interpreted.

Prof Song said: “The asymptomatic cases identified in the screening programme in Wuhan were truly asymptomatic, as none of them showed clinical symptoms before or during their follow-up isolation.

“But there is plenty of evidence elsewhere showing people infected with Covid-19 may be temporarily asymptomatic and infectious before going on to develop symptoms.

“It’s also very important to say these asymptomatic cases were identified shortly after the relaxation of a very stringent lockdown in Wuhan that lasted more than 70 days. By then, the epidemic in Wuhan had been effectively brought under control."

Prof Song said it would be "problematic" to apply the research results to countries where Covid-19 outbreaks have not been successfully brought under control.

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