Harnessing T-Cells for Enhanced Vaccine Development against Viral Infections.

Despite significant strides in vaccine research and the availability of vaccines for many infectious diseases, the threat posed by both known and emerging infectious diseases persists. Moreover, breakthrough infections following vaccination remain a concern. Therefore, the development of novel vaccines is imperative. These vaccines must exhibit robust protective efficacy, broad-spectrum coverage, and long-lasting immunity. One promising avenue in vaccine development lies in leveraging T-cells, which play a crucial role in adaptive immunity and regulate immune responses during viral infections. T-cell recognition can target highly variable or conserved viral proteins, and memory T-cells offer the potential for durable immunity. Consequently, T-cell-based vaccines hold promise for advancing vaccine development efforts. This review delves into the latest research advancements in T-cell-based vaccines across various platforms and discusses the associated challenges.

Altered effective connectivity on rapid automatized naming deficits in Chinese children with developmental dyslexia: An rs-fMRI study with Ganger causality analysis.

Rapid Automatized Naming (RAN) is the core defect of developmental dyslexia (DD), requiring collaboration among brain areas to complete. However, it's still unclear which effective connectivity (EC) among brain areas are crucial for RAN deficits in Chinses children with DD. The current study aims to explore the EC among brain areas related to RAN deficits in Chinese children with DD. We recruited 36 Chinese children with DD and 64 typically developing (TD) children aged 8-12 to complete resting-state functional magnetic resonance imaging (rs-fMRI) scan. Granger causality analysis (GCA) was employed to analysis the EC among brain areas related to RAN, and to calculate the relationship between EC and RAN scores. Compared to TD group, the DD group exhibited significantly decreased EC from left precentral gyrus (PG) to right precuneus, left anterior cingulate and paracingulate gyrus (ACG), left calcarine and right angular, from left middle frontal gyrus (MFG) to left calcarine. Additionally, the DD group showed increased EC from right cuneus to left inferior frontal gyrus triangular part (IFGtri). The EC from left PG to left ACG was positively correlated with letters-RAN score. The results showed Chinese children with DD had both defect and compensatory mechanisms for their RAN deficits. The decreased EC output from left PG may be the core problem of the RAN deficits, which may influence the integration of visual-spatial information, attention, memory retrieval, and speech motor in speech production. The current study has important clinic implications for establishing intervention measures targeted brain.

Characterization of humoral immune responses against SARS-CoV-2 accessory proteins in infected patients and mouse model.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, encodes several accessory proteins that have been shown to play crucial roles in regulating the innate immune response. However, their expressions in infected cells and immunogenicity in infected humans and mice are still not fully understood. This study utilized various techniques such as luciferase immunoprecipitation system (LIPS), immunofluorescence â€‹assay (IFA), and western â€‹blot (WB) to detect accessory protein-specific antibodies in sera of COVID-19 patients. Specific antibodies to proteins 3a, 3b, 7b, 8 and 9c can be detected by LIPS, but only protein 3a antibody was detected by IFA or WB. Antibodies against proteins 3a and 7b were only detected in ICU patients, which may serve as a marker for predicting disease progression. Further, we investigated the expression of accessory proteins in SARS-CoV-2-infected cells and identified the expressions of proteins 3a, 6, 7a, 8, and 9b. We also analyzed their ability to induce antibodies in immunized mice and found that only proteins 3a, 6, 7a, 8, 9b and 9c were able to induce measurable antibody productions, but these antibodies lacked neutralizing activities and did not protect mice from SARS-CoV-2 infection. Our findings validate the expression of SARS-CoV-2 accessory proteins and elucidate their humoral immune response, providing a basis for protein detection assays and their role in pathogenesis.

Discovery of natural catechol derivatives as covalent SARS-CoV-2 3CLpro inhibitors.

The COVID-19 pandemic caused by SARS-CoV-2 continues to pose a threat to public health, and extensive research by scientists worldwide has also prompted the development of antiviral therapies. The 3C-like protease (3CLpro) is critical for SARS-CoV-2 replication and acts as an effective target for drug development. To date, numerous of natural products have been reported to exhibit inhibitory effects on 3CLpro, which encourages us to identify other novel inhibitors and elucidate their mechanism of action. In this study, we first screened an in-house compound library of 101 natural products using FRET assay, and found that oleuropein showed good inhibitory activity against SARS CoV-2 3CLpro with an IC50 value of 4.18 µM. Further studies revealed that the catechol core is essential for activity and can covalently bind to SARS-CoV-2 3CLpro. Among other 45 catechol derivatives, wedelolactone, capsazepine and brazilin showed better SARS-CoV-2 3CLpro inhibitory activities with IC50 values of 1.35 µM, 1.95 µM and 1.18 µM, respectively. These catechol derivatives were verified to be irreversible covalent inhibitors by time-dependent experiments, enzymatic kinetic studies, dilution and dialysis assays. It also exhibited good selectivity towards different cysteine proteases (SARS-CoV-2 PLpro, cathepsin B and cathepsin L). Subsequently, the binding affinity between brazilin and SARS-CoV-2 3CLpro was determined by SPR assay with KD value of 0.80 µM. Molecular dynamic (MD) simulations study showed the binding mode of brazilin in the target protein. In particular, brazilin displayed good anti-SARS-CoV-2 activity in A549-hACE2-TMPRSS2 cells with EC50 values of 7.85 ± 0.20 µM and 5.24 ± 0.21 µM for full time and post-infection treatments, respectively. This study provides a promising lead compound for the development of novel anti-SARS-CoV-2 drugs.

SARS-CoV-2 immunity in animal models.

The COVID-19 pandemic, which was caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a worldwide health crisis due to its transmissibility. SARS-CoV-2 infection results in severe respiratory illness and can lead to significant complications in affected individuals. These complications encompass symptoms such as coughing, respiratory distress, fever, infectious shock, acute respiratory distress syndrome (ARDS), and even multiple-organ failure. Animal models serve as crucial tools for investigating pathogenic mechanisms, immune responses, immune escape mechanisms, antiviral drug development, and vaccines against SARS-CoV-2. Currently, various animal models for SARS-CoV-2 infection, such as nonhuman primates (NHPs), ferrets, hamsters, and many different mouse models, have been developed. Each model possesses distinctive features and applications. In this review, we elucidate the immune response elicited by SARS-CoV-2 infection in patients and provide an overview of the characteristics of various animal models mainly used for SARS-CoV-2 infection, as well as the corresponding immune responses and applications of these models. A comparative analysis of transcriptomic alterations in the lungs from different animal models revealed that the K18-hACE2 and mouse-adapted virus mouse models exhibited the highest similarity with the deceased COVID-19 patients. Finally, we highlighted the current gaps in related research between animal model studies and clinical investigations, underscoring lingering scientific questions that demand further clarification.

Identification of a highly conserved neutralizing epitope within the RBD region of diverse SARS-CoV-2 variants.

The constant emergence of SARS-CoV-2 variants continues to impair the efficacy of existing neutralizing antibodies, especially XBB.1.5 and EG.5, which showed exceptional immune evasion properties. Here, we identify a highly conserved neutralizing epitope targeted by a broad-spectrum neutralizing antibody BA7535, which demonstrates high neutralization potency against not only previous variants, such as Alpha, Beta, Gamma, Delta and Omicron BA.1-BA.5, but also more recently emerged Omicron subvariants, including BF.7, CH.1.1, XBB.1, XBB.1.5, XBB.1.9.1, EG.5. Structural analysis of the Omicron Spike trimer with BA7535-Fab using cryo-EM indicates that BA7535 recognizes a highly conserved cryptic receptor-binding domain (RBD) epitope, avoiding most of the mutational hot spots in RBD. Furthermore, structural simulation based on the interaction of BA7535-Fab/RBD complexes dissects the broadly neutralizing effect of BA7535 against latest variants. Therapeutic and prophylactic treatment with BA7535 alone or in combination with BA7208 protected female mice from the circulating Omicron BA.5 and XBB.1 variant infection, suggesting the highly conserved neutralizing epitope serves as a potential target for developing highly potent therapeutic antibodies and vaccines.

Identification of a broad sarbecovirus neutralizing antibody targeting a conserved epitope on the receptor-binding domain.

Omicron, as the emerging variant with enhanced vaccine tolerance, has sharply disrupted most therapeutic antibodies. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) belongs to the subgenus Sarbecovirus, members of which share high sequence similarity. Herein, we report one sarbecovirus antibody, 5817, which has broad-spectrum neutralization capacity against SARS-CoV-2 variants of concern (VOCs) and SARS-CoV, as well as related bat and pangolin viruses. 5817 can hardly compete with six classes of receptor-binding-domain-targeted antibodies grouped by structural classifications. No obvious impairment in the potency is detected against SARS-CoV-2 Omicron and subvariants. The cryoelectron microscopy (cryo-EM) structure of neutralizing antibody 5817 in complex with Omicron spike reveals a highly conserved epitope, only existing at the receptor-binding domain (RBD) open state. Prophylactic and therapeutic administration of 5817 potently protects mice from SARS-CoV-2 Beta, Delta, Omicron, and SARS-CoV infection. This study reveals a highly conserved cryptic epitope targeted by a broad sarbecovirus neutralizing antibody, which would be beneficial to meet the potential threat of pre-emergent SARS-CoV-2 VOCs.

Mosaic RBD Nanoparticles Elicit Protective Immunity Against Multiple Human Coronaviruses in Animal Models.

To combat SARS-CoV-2 variants and MERS-CoV, as well as the potential re-emergence of SARS-CoV and spillovers of sarbecoviruses, which pose a significant threat to global public health, vaccines that can confer broad-spectrum protection against betacoronaviruses (ß-CoVs) are urgently needed. A mosaic ferritin nanoparticle vaccine is developed that co-displays the spike receptor-binding domains of SARS-CoV, MERS-CoV, and SARS-CoV-2 Wild-type (WT) strain and evaluated its immunogenicity and protective efficacy in mice and nonhuman primates. A low dose of 10 µg administered at a 21-day interval induced a Th1-biased immune response in mice and elicited robust cross-reactive neutralizing antibody responses against a variety of ß-CoVs, including a series of SARS-CoV-2 variants. It is also able to effectively protect against challenges of SARS-CoV, MERS-CoV, and SARS-CoV-2 variants in not only young mice but also the more vulnerable mice through induction of long-lived immunity. Together, these results suggest that this mosaic 3-RBD nanoparticle has the potential to be developed as a pan-ß-CoV vaccine.

P21-activated kinase 1 (PAK1)-mediated cytoskeleton rearrangement promotes SARS-CoV-2 entry and ACE2 autophagic degradation.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has had a significant impact on healthcare systems and economies worldwide. The continuous emergence of new viral strains presents a major challenge in the development of effective antiviral agents. Strategies that possess broad-spectrum antiviral activities are desirable to control SARS-CoV-2 infection. ACE2, an angiotensin-containing enzyme that prevents the overactivation of the renin angiotensin system, is the receptor for SARS-CoV-2. ACE2 interacts with the spike protein and facilitates viral attachment and entry into host cells. Yet, SARS-CoV-2 infection also promotes ACE2 degradation. Whether restoring ACE2 surface expression has an impact on SARS-CoV-2 infection is yet to be determined. Here, we show that the ACE2-spike complex is endocytosed and degraded via autophagy in a manner that depends on clathrin-mediated endocytosis and PAK1-mediated cytoskeleton rearrangement. In contrast, free cellular spike protein is selectively cleaved into S1 and S2 subunits in a lysosomal-dependent manner. Importantly, we show that the pan-PAK inhibitor FRAX-486 restores ACE2 surface expression and suppresses infection by different SARS-CoV-2 strains. FRAX-486-treated Syrian hamsters exhibit significantly decreased lung viral load and alleviated pulmonary inflammation compared with untreated hamsters. In summary, our findings have identified novel pathways regulating viral entry, as well as therapeutic targets and candidate compounds for controlling the emerging strains of SARS-CoV-2 infection.

Plasma cell-free DNA promise monitoring and tissue injury assessment of COVID-19.

Coronavirus 2019 (COVID-19) is a complex disease that affects billions of people worldwide. Currently, effective etiological treatment of COVID-19 is still lacking; COVID-19 also causes damages to various organs that affects therapeutics and mortality of the patients. Surveillance of the treatment responses and organ injury assessment of COVID-19 patients are of high clinical value. In this study, we investigated the characteristic fragmentation patterns and explored the potential in tissue injury assessment of plasma cell-free DNA in COVID-19 patients. Through recruitment of 37 COVID-19 patients, 32 controls and analysis of 208 blood samples upon diagnosis and during treatment, we report gross abnormalities in cfDNA of COVID-19 patients, including elevated GC content, altered molecule size and end motif patterns. More importantly, such cfDNA fragmentation characteristics reflect patient-specific physiological changes during treatment. Further analysis on cfDNA tissue-of-origin tracing reveals frequent tissue injuries in COVID-19 patients, which is supported by clinical diagnoses. Hence, our work demonstrates and extends the translational merit of cfDNA fragmentation pattern as valuable analyte for effective treatment monitoring, as well as tissue injury assessment in COVID-19.

Successful clearance of persistent SARS-CoV-2 asymptomatic infection following a single dose of Ad5-nCoV vaccine.

Persistent asymptomatic (PA) SARS-CoV-2 infections have been identified. The immune responses in these patients are unclear, and the development of effective treatments for these patients is needed. Here, we report a cohort of 23 PA cases carrying viral RNA for up to 191 days. PA cases displayed low levels of inflammatory and interferon response, weak antibody response, diminished circulating follicular helper T cells (cTfh), and inadequate specific CD4+ and CD8+ T-cell responses during infection, which is distinct from symptomatic infections and resembling impaired immune activation. Administration of a single dose of Ad5-nCoV vaccine to 10 of these PA cases elicited rapid and robust antibody responses as well as coordinated B-cell and cTfh responses, resulting in successful viral clearance. Vaccine-induced antibodies were able to neutralize various variants of concern and persisted for over 6 months, indicating long-term protection. Therefore, our study provides an insight into the immune status of PA infections and highlights vaccination as a potential treatment for prolonged SARS-CoV-2 infections.

Mouse models susceptible to HCoV-229E and HCoV-NL63 and cross protection from challenge with SARS-CoV-2.

Human coronavirus 229E (HCoV-229E) and NL63 (HCoV-NL63) are endemic causes of upper respiratory infections such as the "common cold" but may occasionally cause severe lower respiratory tract disease in the elderly and immunocompromised patients. There are no approved antiviral drugs or vaccines for these common cold coronaviruses (CCCoV). The recent emergence of COVID-19 and the possible cross-reactive antibody and T cell responses between these CCCoV and SARS-CoV-2 emphasize the need to develop experimental animal models for CCCoV. Mice are an ideal experimental animal model for such studies, but are resistant to HCoV-229E and HCoV-NL63 infections. Here, we generated 229E and NL63 mouse models by exogenous delivery of their receptors, human hAPN and hACE2 using replication-deficient adenoviruses (Ad5-hAPN and Ad5-hACE2), respectively. Ad5-hAPN- and Ad5-hACE2-sensitized IFNAR-/- and STAT1-/- mice developed pneumonia characterized by inflammatory cell infiltration with virus clearance occurring 7 d post infection. Ad5-hAPN- and Ad5-hACE2-sensitized mice generated virus-specific T cells and neutralizing antibodies after 229E or NL63 infection, respectively. Remdesivir and a vaccine candidate targeting spike protein of 229E and NL63 accelerated viral clearance of virus in these mice. 229E- and NL63-infected mice were partially protected from SARS-CoV-2 infection, likely mediated by cross-reactive T cell responses. Ad5-hAPN- and Ad5-hACE2-transduced mice are useful for studying pathogenesis and immune responses induced by HCoV-229E and HCoV-NL63 infections and for validation of broadly protective vaccines, antibodies, and therapeutics against human respiratory coronaviruses including SARS-CoV-2.

What factors can support students' deep learning in the online environment: The mediating role of learning self-efficacy and positive academic emotions?

Introduction: In 2020, COVID-19 forced higher education institutions in many countries to turn to online distance learning. The trend of using online education has accelerated across the world. However, this change in the teaching mode has led to the decline of students' online learning quality and resulted in students being unable to do deep learning. Therefore, the current research, aimed at promoting deep learning in the online environment, constructed a theoretical model with learning self-efficacy and positive academic emotions as mediators, deep learning as the dependent variable, perceived TPACK support, peer support, technical usefulness, and ease of use as independent variables. Methods: The theoretical model was verified by SPSS26.0 and smartPLS3.0, and to assess the measurement and structural models, the PLS approach to structural equation modeling (SEM) was performed. Results: The study found that (a) positive academic emotions play a mediating role between perceived TPACK support and deep learning, perceived peer support and deep learning, and perceived technology usefulness and ease of use and deep learning; (b) learning self-efficacy plays a mediating role between perceived TPACK support and deep learning, perceived peer support and deep learning, and perceived technology usefulness and ease of use and deep learning. Discussion: The findings of this study fill the gaps in the research on the theoretical models of deep learning in the online environment and provide a theoretical basis for online teaching, learning quality, and practical improvement strategies.

Virus-Specific Regulatory T Cells Persist as Memory in a Neurotropic Coronavirus Infection.

Regulatory T cells (Tregs) are critical for regulating immunopathogenic responses in a variety of infections, including infection of mice with JHM strain of mouse hepatitis virus (JHMV), a neurotropic coronavirus that causes immune-mediated demyelinating disease. Although virus-specific Tregs are known to mitigate disease in this infection by suppressing pathogenic effector T cell responses of the same specificity, it is unclear whether these virus-specific Tregs form memory populations and persist similar to their conventional T cell counterparts of the same epitope specificity. Using congenically labeled JHMV-specific Tregs, we found that virus-specific Tregs persist long-term after murine infection, through at least 180 d postinfection and stably maintain Foxp3 expression. We additionally demonstrate that these cells are better able to proliferate and inhibit virus-specific T cell responses postinfection than naive Tregs of the same specificity, further suggesting that these cells differentiate into memory Tregs upon encountering cognate Ag. Taken together, these data suggest that virus-specific Tregs are able to persist long-term in the absence of viral Ag as memory Tregs.

Plasma cell-free RNA characteristics in COVID-19 patients.

The pathogenesis of COVID-19 is still elusive, which impedes disease progression prediction, differential diagnosis, and targeted therapy. Plasma cell-free RNAs (cfRNAs) carry unique information from human tissue and thus could point to resourceful solutions for pathogenesis and host-pathogen interactions. Here, we performed a comparative analysis of cfRNA profiles between COVID-19 patients and healthy donors using serial plasma. Analyses of the cfRNA landscape, potential gene regulatory mechanisms, dynamic changes in tRNA pools upon infection, and microbial communities were performed. A total of 380 cfRNA molecules were up-regulated in all COVID-19 patients, of which seven could serve as potential biomarkers (AUC > 0.85) with great sensitivity and specificity. Antiviral (NFKB1A, IFITM3, and IFI27) and neutrophil activation (S100A8, CD68, and CD63)-related genes exhibited decreased expression levels during treatment in COVID-19 patients, which is in accordance with the dynamically enhanced inflammatory response in COVID-19 patients. Noncoding RNAs, including some microRNAs (let 7 family) and long noncoding RNAs (GJA9-MYCBP) targeting interleukin (IL6/IL6R), were differentially expressed between COVID-19 patients and healthy donors, which accounts for the potential core mechanism of cytokine storm syndromes; the tRNA pools change significantly between the COVID-19 and healthy group, leading to the accumulation of SARS-CoV-2 biased codons, which facilitate SARS-CoV-2 replication. Finally, several pneumonia-related microorganisms were detected in the plasma of COVID-19 patients, raising the possibility of simultaneously monitoring immune response regulation and microbial communities using cfRNA analysis. This study fills the knowledge gap in the plasma cfRNA landscape of COVID-19 patients and offers insight into the potential mechanisms of cfRNAs to explain COVID-19 pathogenesis.

Two novel human coronavirus OC43 genotypes circulating in hospitalized children with pneumonia in China.

HCoV-OC43 is one of the mildly pathogenic coronaviruses with high infection rates in common population. Here, 43 HCoV-OC43 related cases with pneumonia were reported, corresponding genomes of HCoV-OC43 were obtained. Phylogenetic analyses based on complete genome, orf1ab and spike genes revealed that two novel genotypes of HCoV-OC43 have emerged in China. Obvious recombinant events also can be detected in the analysis of the evolutionary dynamics of novel HCoV-OC43 genotypes. Estimated divergence time analysis indicated that the two novel genotypes had apparently independent evolutionary routes. Efforts should be conducted for further investigation of genomic diversity and evolution analysis of mildly pathogenic coronaviruses.

The N-Terminal Region of Middle East Respiratory Syndrome Coronavirus Accessory Protein 8b Is Essential for Enhanced Virulence of an Attenuated Murine Coronavirus.

Middle East respiratory syndrome coronavirus (MERS-CoV) is a beta coronavirus that emerged in 2012, causing severe pneumonia and renal failure. MERS-CoV encodes five accessory proteins. Some of them have been shown to interfere with host antiviral immune response. However, the roles of protein 8b in innate immunity and viral virulence was rarely studied. Here, we introduced individual MERS-CoV accessory protein genes into the genome of an attenuated murine coronavirus (Mouse hepatitis virus, MHV), respectively, and found accessory protein 8b could enhance viral replication in vivo and in vitro and increase the lethality of infected mice. RNA-seq analysis revealed that protein 8b could significantly inhibit type I interferon production (IFN-I) and innate immune response in mice infected with MHV expressing protein 8b. We also found that MERS-CoV protein 8b could initiate from multiple internal methionine sites and at least three protein variants were identified. Residues 1-23 of protein 8b was demonstrated to be responsible for increased virulence in vivo. In addition, the inhibitory effect on IFN-I of protein 8b might not contribute to its virulence enhancement as aa1-23 deletion did not affect IFN-I production in vitro and in vivo. Next, we also found that protein 8b was localized to the endoplasmic reticulum (ER)/Golgi membrane in infected cells, which was disrupted by C-terminal region aa 88-112 deletion. This study will provide new insight into the pathogenesis of MERS-CoV infection. IMPORTANCE Multiple coronaviruses (CoV) cause severe respiratory infections and become global public health threats such as SARS-CoV, MERS-CoV, and SARS-CoV-2. Each coronavirus contains different numbers of accessory proteins which show high variability among different CoVs. Accessory proteins are demonstrated to play essential roles in pathogenesis of CoVs. MERS-CoV contains 5 accessory proteins (protein 3, 4a, 4b, 5, 8b), and deletion of all four accessory proteins (protein 3, 4a, 4b, 5), significantly affects MERS-CoV replication and pathogenesis. However, whether ORF8b also regulates MERS-CoV infection is unknown. Here, we constructed mouse hepatitis virus (MHV) recombinant virus expressing MERS-CoV protein 8b and demonstrated protein 8b could significantly enhance the virulence of MHV, which is mediated by N-terminal domain of protein 8b. This study will shed light on the understanding of pathogenesis of MERS-CoV infection.

Detection of Anti-SARS-CoV-2-S2 IgG Is More Sensitive Than Anti-RBD IgG in Identifying Asymptomatic COVID-19 Patients.

Characterizing the serologic features of asymptomatic SARS-CoV-2 infection is imperative to improve diagnostics and control of SARS-CoV-2 transmission. In this study, we evaluated the antibody profiles in 272 plasma samples collected from 59 COVID-19 patients, consisting of 18 asymptomatic patients, 33 mildly ill patients and 8 severely ill patients. We measured the IgG against five viral structural proteins, different isotypes of immunoglobulins against the Receptor Binding Domain (RBD) protein, and neutralizing antibodies. The results showed that the overall antibody response was lower in asymptomatic infections than in symptomatic infections throughout the disease course. In contrast to symptomatic patients, asymptomatic patients showed a dominant IgG-response towards the RBD protein, but not IgM and IgA. Neutralizing antibody titers had linear correlations with IgA/IgM/IgG levels against SARS-CoV-2-RBD, as well as with IgG levels against multiple SARS-CoV-2 structural proteins, especially with anti-RBD or anti-S2 IgG. In addition, the sensitivity of anti-S2-IgG is better in identifying asymptomatic infections at early time post infection compared to anti-RBD-IgG. These data suggest that asymptomatic infections elicit weaker antibody responses, and primarily induce IgG antibody responses rather than IgA or IgM antibody responses. Detection of IgG against the S2 protein could supplement nucleic acid testing to identify asymptomatic patients. This study provides an antibody detection scheme for asymptomatic infections, which may contribute to epidemic prevention and control.