A mass screening programme of more than 10 million Wuhan residents identified 300 asymptomatic cases, but none were infectious. The results are published in the journal Nature Communications.
The mass testing project 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 the close contacts of these positive asymptomatic cases did not test positive. The researchers, however, cautioned that their findings do not show that the virus cannot be transmitted by asymptomatic carriers. What this means, instead, is that strict non-pharmaceutical interventions such as mask-wearing, hand washing, social distancing and lockdown have helped reduce the virulence of Covid-19.
The study was led by researchers at the Huazhong University of Science and Technology (HUST) in Wuhan, China, in collaboration with researchers at the Norwich Medical School, University of East Anglia, UK.
Wuhan was the most seriously affected city in China. After stringent interventions and lockdown measures from January 23, the city’s lockdown was lifted on April 8. The mass screening was carried out between May 14 and June 1, to assess the post-lockdown risk of Covid-19.
The 300 asymptomatic cases were found among people aged between 10 and 89. The asymptomatic positive rate was the lowest in children and teens aged under 17, and the highest among people aged over 60. Further swab testing of 1,174 close contacts of these 300 asymptomatic positive cases were all negative. 📣 Express Explained is now on Telegram
What the findings showed, in effect, was that the infection prevalence was very low 5-8 weeks after the end of lockdown. The researchers said this confirms that transmission of Covid-19 can be successfully controlled by well implemented interventions, including mask wearing, hand hygiene, social distancing, contract tracing, and lockdown restrictions.
But while the cases identified in Wuhan were asymptomatic, there is plenty of evidence elsewhere showing that people infected with Covid-19 may be temporarily asymptomatic and infectious before going on to develop symptoms. Also, the asymptomatic cases in Wuhan were identified after a very stringent lockdown — by then, the epidemic had been already brought under control.
Again, antibody testing showed that almost two-thirds of the asymptomatic cases had previously had Covid-19. Because the risk of people being infected was greatly reduced, when people are exposed to a low dose of virus, they may tend to be asymptomatic as a result of their own immunity. Therefore, the researchers stressed, it would be problematic to apply the results of this research to countries where Covid-19 outbreaks have not been successfully brought under control.
Source: University of East Anglia
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