Coronavirus disease 2019 (COVID-19) represents a global crisis, yet major knowledge gaps remain about human immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We analyzed immune responses in 76 COVID-19 patients and 69 healthy individuals from Hong Kong and Atlanta, Georgia, United States. In the peripheral blood mononuclear cells (PBMCs) of COVID-19 patients, we observed reduced expression of human leukocyte antigen class DR (HLA-DR) and proinflammatory cytokines by myeloid cells as well as impaired mammalian target of rapamycin (mTOR) signaling and interferon-α (IFN-α) production by plasmacytoid dendritic cells. By contrast, we detected enhanced plasma levels of inflammatory mediators—including EN-RAGE, TNFSF14, and oncostatin M—which correlated with disease severity and increased bacterial products in plasma. Single-cell transcriptomics revealed a lack of type I IFNs, reduced HLA-DR in the myeloid cells of patients with severe COVID-19, and transient expression of IFN-stimulated genes. This was consistent with bulk PBMC transcriptomics and transient, low IFN-α levels in plasma during infection. These results reveal mechanisms and potential therapeutic targets for COVID-19.

SARS-CoV-2 has affected over 9 million patients with more than 460,000 deaths in about 6 months. Understanding the factors that contribute to e cient SARS-CoV-2 infection of human cells, which are not previously reported, may provide insights on SARS-CoV-2 transmissibility and pathogenesis, and reveal targets of intervention. Here, we reported key host and viral determinants that were essential for e cient SARS-CoV-2 infection in the human lung. First, we identi ed heparan sulfate as an important attachment factor for SARS-CoV-2 infection. Second, we demonstrated that while cell surface sialic acids signi cantly restricted SARS-CoV infection, SARS-CoV-2 could largely overcome sialic acid-mediated restriction in both human lung epithelial cells and ex vivo human lung tissue explants. Third, we demonstrated that the inserted furin-like cleavage site in SARS-CoV-2 spike was required for e cient virus replication in human lung but not intestine tissues. Overall, these ndings contributed to our understanding on e cient SARS-CoV-2 infection of human lungs.

39 On 31 st December 2019, the World Health Organization was informed of a cluster of cases of 40 pneumonia of unknown etiology in Wuhan, China. Subsequent investigations identified a novel 41 coronavirus, now named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), 42 from the affected patients. Highly sensitive and specific laboratory diagnostics are important for 43 controlling the rapidly evolving SARS-CoV-2-associated Coronavirus Disease 2019 (COVID-44 19) epidemic. In this study, we developed and compared the performance of three novel real-time 45 RT-PCR assays targeting the RNA-dependent RNA polymerase (RdRp)/helicase (Hel), spike (S), 46 and nucleocapsid (N) genes of SARS-CoV-2 with that of the reported RdRp-P2 assay which is 47 used in >30 European laboratories. Among the three novel assays, the COVID-19-RdRp/Hel 48 assay had the lowest limit of detection in vitro (1.8 TCID 50 /ml with genomic RNA and 11.2 RNA 49 copies/reaction with in vitro RNA transcripts). Among 273 specimens from 15 patients with 50 laboratory-confirmed COVID-19 in Hong Kong, 77 (28.2%) were positive by both the COVID-51 19-RdRp/Hel and RdRp-P2 assays. The COVID-19-RdRp/Hel assay was positive for an 52 additional 42 RdRd-P2-negative specimens [119/273 (43.6%) vs 77/273 (28.2%), P<0.001], 53including 29/120 (24.2%) respiratory tract specimens and 13/153 (8.5%) non-respiratory tract 54 specimens. The mean viral load of these specimens was 3.21×10 4 RNA copies/ml (range, 55 2.21×10 2 to 4.71×10 5 RNA copies/ml). The COVID-19-RdRp/Hel assay did not cross-react with 56 other human-pathogenic coronaviruses and respiratory pathogens in cell culture and clinical 57 specimens, whereas the RdRp-P2 assay cross-reacted with SARS-CoV in cell culture. The highly 58 sensitive and specific COVID-19-RdRp/Hel assay may help to improve the laboratory diagnosis 59 of COVID-19. 60 61 on March 16, 2020 by guest http://jcm.asm.org/ Downloaded from 4

word count 250) Background: To describe the infection control preparedness for Coronavirus Disease (COVID-19) due to SARS-CoV-2 [previously known as 2019-novel coronavirus] in the first 42 days after announcement of a cluster of pneumonia in China, on 31 December 2019 (day 1) in Hong Kong. Methods:A bundle approach of active and enhanced laboratory surveillance, early airborne infection isolation, rapid molecular diagnostic testing, and contact tracing for healthcare workers (HCWs) with unprotected exposure in the hospitals was implemented.Epidemiological characteristics of confirmed cases, environmental and air samples were collected and analyzed.

Background The ongoing coronavirus disease (COVID-19) pandemic has major impacts on health systems, the economy and society. Assessing infection attack rates in the population is critical for estimating disease severity and herd immunity which is needed to calibrate public health interventions. We have previously shown that it is possible to achieve this in real time to impact public health decision making. Aim Our objective was to develop and evaluate serological assays applicable in large-scale sero-epidemiological studies. Methods We developed an ELISA to detect IgG and IgM antibodies to the receptor-binding domain (RBD) of the spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated its sensitivity and specificity in combination with confirmatory microneutralisation (MN) and 90% plaque reduction neutralisation tests (PRNT90) in 51 sera from 24 patients with virologically confirmed COVID-19 and in age-stratified sera from 200 healthy controls. Results IgG and IgM RBD ELISA, MN and PRNT90 were reliably positive after 29 days from illness onset with no detectable cross-reactivity in age-stratified controls. We found that PRNT90 tests were more sensitive in detecting antibody than MN tests carried out with the conventional 100 tissue culture infectious dose challenge. Heparinised plasma appeared to reduce the infectivity of the virus challenge dose and may confound interpretation of neutralisation test. Conclusion Using IgG ELISA based on the RBD of the spike protein to screen sera for SARS-CoV-2 antibody, followed by confirmation using PRNT90, is a valid approach for large-scale sero-epidemiology studies.