I honestly don’t know what to make of this study in Nature. Here’s the abstract:
Stringent COVID-19 control measures were imposed in Wuhan between January 23 and April 8, 2020. Estimates of the prevalence of infection following the release of restrictions could inform post-lockdown pandemic management. Here, we describe a city-wide SARS-CoV-2 nucleic acid screening programme between May 14 and June 1, 2020 in Wuhan. All city residents aged six years or older were eligible and 9,899,828 (92.9%) participated. No new symptomatic cases and 300 asymptomatic cases (detection rate 0.303/10,000, 95% CI 0.270–0.339/10,000) were identified. There were no positive tests amongst 1,174 close contacts of asymptomatic cases. 107 of 34,424 previously recovered COVID-19 patients tested positive again (re-positive rate 0.31%, 95% CI 0.423–0.574%). The prevalence of SARS-CoV-2 infection in Wuhan was therefore very low five to eight weeks after the end of lockdown.
Virus cultures were negative for all asymptomatic positive and repositive cases, indicating no “viable virus” in positive cases detected in this study.
while from the discussion section:
This study has several limitations that need to be discussed. First, this was a cross-sectional screening programme, and we are unable to assess the changes over time in asymptomatic positive and reoperative results. Second, although a positive result of nucleic acid testing reveals the existence of the viral RNAs, some false negative results were likely to have occurred, in particular due to the relatively low level of virus loads in asymptomatic infected individuals, inadequate collection of samples, and limited accuracy of the testing technology13. Although the screening programme provided no direct evidence on the sensitivity and specificity of the testing method used, a meta-analysis reported a pooled sensitivity of 73% (95% CI 68–78%) for nasopharayngeal and throat swab testing of COVID-1914. Testing kits used in the screening programme were publicly purchased by the government and these kits have been widely used in China and other countries.
I also have a question: how did they define “asymptomatic”?
I have reservations about this study not for the least because of its origins. However, if true, doesn’t it suggest that the approach taken by governors in most states has been wrong? The necessary mitigation would appear to be mandatory quarantining of the symptomatic. And that wearing masks and social distancing is most effective when practiced by the symptomatic. While distasteful is that not a lot more manageable with fewer adverse consequences than shuttering businesses?