Objective We aim to systematically review the characteristics of asymptomatic infection in the coronavirus disease 2019 (COVID‐19). Methods PubMed and EMBASE were electronically searched to identify original studies containing the rate of asymptomatic infection in COVID‐19 patients before 20 May 2020. Then mate‐analysis was conducted using R version 3.6.2. Results A total of 50155 patients from 41 studies with confirmed COVID‐19 were included. The pooled percentage of asymptomatic infection is 15.6% (95% CI: 10.1%‐23.0%). Ten included studies contain the number of pre‐symptomatic patients, who were asymptomatic at screening point and developed symptoms during follow‐up. The pooled percentage of pre‐symptomatic infection among 180 initially asymptomatic patients is 48.9% (95% CI: 31.6‐66.2%). The pooled proportion of asymptomatic infection among 1152 COVID‐19 children from 11 studies is 27.7% (95% CI: 16.4–42.7%), which is much higher than patients from all aged groups. Abnormal CT features are common in asymptomatic COVID‐19 infection. For 36 patients from 4 studies that CT results were available, 15 (41.7%) patients had bilateral involvement and 14 (38.9%) had unilateral involvement in CT results. Reduced white blood cell count, increased lactate dehydrogenase, and increased C‐reactive protein were also recorded. Conclusion About 15.6% of confirmed COVID‐19 patients are asymptomatic. Nearly half of the patients with no symptoms at detection time will develop symptoms later. Children are likely to have a higher proportion of asymptomatic infection than adults. Asymptomatic COVID‐19 patients could have abnormal laboratory and radiational manifestations which can be used as screening strategies to identify asymptomatic infection. This article is protected by copyright. All rights reserved.

The zinc finger antiviral protein (ZAP) is a mammalian host restriction factor that inhibits the replication of a variety of RNA viruses, including retroviruses, alphaviruses and filoviruses, through interaction with the ZAP-responsive elements (ZRE) in viral RNA, and recruiting the exosome to degrade RNA substrate. Hepatitis B virus (HBV) is a pararetrovirus that replicates its genomic DNA via reverse transcription of a viral pregenomic (pg) RNA precursor. Here, we demonstrate that the two isoforms of human ZAP (hZAP-L and -S) inhibit HBV replication in human hepatocyte-derived cells through posttranscriptional down-regulation of viral pgRNA. Mechanistically, the zinc finger motif-containing N-terminus of hZAP is responsible for the reduction of HBV RNA, and the integrity of the four zinc finger motifs is essential for ZAP to bind to HBV RNA and fulfill its antiviral function. The ZRE sequences conferring the susceptibility of viral RNA to ZAP-mediated RNA decay were mapped to the terminal redundant region (nt 1820–1918) of HBV pgRNA. In agreement with its role as a host restriction factor and as an innate immune mediator for HBV infection, ZAP was upregulated in cultured primary human hepatocytes and hepatocyte-derived cells upon IFN-α treatment or IPS-1 activation, and in the livers of hepatitis B patients during immune active phase. Knock down of ZAP expression increased the level of HBV RNA and partially attenuated the antiviral effect elicited by IPS-1 in cell cultures. In summary, we demonstrated that ZAP is an intrinsic host antiviral factor with activity against HBV through down-regulation of viral RNA, and that ZAP plays a role in the innate control of HBV replication. Our findings thus shed light on virus-host interaction, viral pathogenesis, and antiviral approaches.

Objectives Severe or critical COVID-19 is associated with intensive care unit admission, increased secondary infection rate, and would lead to significant worsened prognosis. Risks and characteristics relating to secondary infections in severe COVID-19 have not been described. Methods Severe and critical COVID-19 patients from Shanghai were included. We collected lower respiratory, urine, catheters, and blood samples according to clinical necessity and culture and mNGS were performed. Clinical and laboratory data were archived. Results We found 57.89% (22/38) patients developed secondary infections. The patient receiving invasive mechanical ventilation or in critical state has a higher chance of secondary infections (P<0.0001). The most common infections were respiratory, bloodstream and urinary infections, and in respiratory infections, the most detected pathogens were gram-negative bacteria (26, 50.00%), following by gram-positive bacteria (14, 26.92%), virus (6, 11.54%), fungi (4, 7.69%), and others (2, 3.85%). Respiratory Infection rate post high flow, tracheal intubation, and tracheotomy were 12.90% (4/31), 30.43% (7/23), and 92.31% (12/13) respectively. Secondary infections would lead to lower discharge rate and higher mortality rate. Conclusion Our study originally illustrated secondary infection proportion in severe and critical COVID-19 patients. Culture accompanied with metagenomics sequencing increased pathogen diagnostic rate. Secondary infections risks increased after receiving invasive respiratory ventilations and intravascular devices, and would lead to a lower discharge rate and a higher mortality rate.