The screening took place after the lockdowns were over. 300 asymptomatic cases in a group of 9,899,828 people. The authors conclude that "The prevalence of SARS-CoV-2 infection in Wuhan was therefore very low five to eight weeks after the end of lockdown." which we can see is pretty much true based on the data.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.
The authors also report:
Further:All asymptomatic positive cases, repositive cases and their close contacts were isolated for at least 2 weeks until the results of nucleic acid testing were negative. None of detected positive cases or their close contacts became symptomatic or newly confirmed with COVID-19 during the isolation period.
And...Previous studies have shown that asymptomatic individuals infected with SARS-CoV-2 virus were infectious3, and might subsequently become symptomatic4. Compared with symptomatic patients, asymptomatic infected persons generally have low quantity of viral loads and a short duration of viral shedding, which decrease the transmission risk of SARS-CoV-25. In the present study, virus culture was carried out on samples from asymptomatic positive cases, and found no viable SARS-CoV-2 virus. All close contacts of the asymptomatic positive cases tested negative, indicating that the asymptomatic positive cases detected in this study were unlikely to be infectious.
There is much more of course and it is subject to discussion and interpretation. I don't know what the other studies are that they refer to, or how the data in those other studies was collected, etc., but IMHO is it premature to conclude from this paper that lockdowns and other precautions are needless.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.
One could just as easily argue that this shows that strict lockdown measures such as those imposed in China are very effective in throttling the spread of the virus, resulting in a very low number of asymptomatic carriers, and that post-lockdown adherence to protective behaviors further reduces the risk of exposure. Contrasting these results with the continuing surge of infections and hospital overloads in the United States indicates that lesser measures clearly do not "work" with the same efficiency as the strict measured imposed in China.
Also...the conclusion by the Twitter personality that spread of the virus by asymptomatic people is not a matter for concern and that lockdowns, etc. are not needed is an oversimplification that assumes that any given person is "asymptomatic" and is thus not contagious, and that he knows better than other experts and organizations. The asymptomatic people in this study may have been contagious previous to the assessment--the study does indicate that none of their close contacts were carriers--but again, they may have had it and cleared it. Thus it is a limitation to the analysis.
Imma wear a mask and stay home as much as possible, considering that infections continue to rise in my neck of the woods.