Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China is the title of a paper published in Nature Communications. First, a few caveats. The article is from China and its content was obviously scrutinized by a repressive regime before it was allowed publication in a western journal. Second, Nature Communications is an open sources journal that claims to be peer reviewed, but I have not been able to determine exactly how such a review operates in that publication. Keeping these reservations in mind, the data in the paper seem believable. The abstract of the report is below. I have underlined the passage of interest here.

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.

 Characteristics of asymptomatic positive individuals (right click to open in a new tab)

This communication reports actions that were only possible under an authoritarian government. A region was completely locked down and everyone in it tested. The message to take from this report is that asymptomatic cases of COVID-19 do not transmit the virus to others. This stance is consistent with other data and I therefore tend to believe it even when considering its dubious source.

The data provide more support for keeping schools open. Virtually all teens and preteens who contract the virus remain asymptomatic and thus are unlikely to infect their teachers or staff if the above is true. They also suggest that routine testing of students is likely a waste of time and money and a source of needless anxiety. The Infectious Disease Society of America does not recommend testing asymptomatic subjects for the flu, a view that should hold for COVID-19 as well.

The following is speculation. Why don’t asymptomatic, as opposed to presymptomatic, subjects with the virus transmit it to others? It may be that these people are asymptomatic because their immune system rapidly inactivates the virus preventing both symptoms and spread. The inactive viral fragments trigger a positive test that is not associated with disease. Just a thought.