A high-throughput fully automatic biosensing platform for efficient COVID-19 detection.

We propose a label-free biosensor based on a porous silicon resonant microcavity and localized surface plasmon resonance. The biosensor detects SARS-CoV-2 antigen based on engineered trimeric angiotensin converting enzyme-2 binding protein, which is conserved across different variants. Robotic arms run the detection process including sample loading, incubation, sensor surface rinsing, and optical measurements using a portable spectrometer. Both the biosensor and the optical measurement system are readily scalable to accommodate testing a wide range of sample numbers. The limit of detection is 100 TCID50/ml. The detection time is 5 min, and the throughput of one single robotic site is up to 384 specimens in 30 min. The measurement interface requires little training, has standard operation, and therefore is suitable for widespread use in rapid and onsite COVID-19 screening or surveillance.

Characterization and pathogenicity of the porcine epidemic diarrhea virus isolated in China.

Piglet diarrhea caused by the porcine epidemic diarrhea virus (PEDV) is a common problem on pig farms in China associated with high morbidity and mortality rates. In this study, three PEDV isolates were successfully detected after the fourth blind passage in Vero cells. The samples were obtained from infected piglet farms in Jilin (Changchun), and Shandong (Qingdao) Provinces of China and were designated as CH/CC-1/2018, CH/CC-2/2018, and CH/QD/2018. According to the analysis of the complete S protein gene sequence, the CH/CC-1/2018 and CH/CC-2/2018 were allocated to the G2b branch, while CH/QD/2018 was located in the G1a interval and was closer to the vaccine strain CV777. Successful detection and identification of the isolated strains were carried out using electron microscopy and indirect immunofluorescence. Meanwhile, animal challenge experiments and viral RNA copies determination were used to compare the pathogenicity. The results showed that CH/CC-1/2018 in Changchun was more pathogenic than CH/QD/2018 in Qingdao. In conclusion, the discovery of these new strains is conducive to the development of vaccines to prevent the pandemic of PEDV, especially that the CH/CC-1/2018, and CH/CC-2/2018 were not related to the classical vaccine strain CV777.

Kinetics of SARS-CoV-2 neutralizing antibodies in Omicron breakthrough cases with inactivated vaccination: Role in inferring the history and duration of infection.

Background: The quantitative level and kinetics of neutralizing antibodies (NAbs) in individuals with Omicron breakthrough infections may differ from those of vaccinated individuals without infection. Therefore, we aimed to evaluate the difference in NAb levels to distinguish the breakthrough cases from the post-immunized population to identify early infected person in an outbreak epidemic when nasal and/or pharyngeal swab nucleic acid real-time PCR results were negative. Methods: We collected 1077 serum samples from 877 individuals, including 189 with Omicron BA.2 breakthrough infection and 688 post-immunized participants. NAb titers were detected using the surrogate virus neutralization test, and were log(2)-transformed to normalize prior to analysis using Student's unpaired t-tests. Geometric mean titers (GMT) were calculated with 95% confidence intervals (CI). Linear regression models were used to identify factors associated with NAb levels. We further conducted ROC curve analysis to evaluate the NAbs' ability to identify breakthrough infected individuals in the vaccinated population. Results: The breakthrough infection group had a consistently higher NAb levels than the post-immunized group according to time since the last vaccination. NAb titers in the breakthrough infection group were 6.4-fold higher than those in the post-immunized group (GMT: 40.72 AU/mL and 6.38 AU/mL, respectively; p<0.0001). In the breakthrough infection group, the NAbs in the convalescent phase were 10.9-fold higher than in the acute phase (GMT: 200.48 AU/mL and 18.46 AU/mL, respectively; p<0.0001). In addition, the time since infection, booster vaccination, and the time since last vaccination were associated with log(2)-transformed NAb levels in the breakthrough infection group. ROC curve analysis showed that ROC area was largest (0.728) when the cut-off value of log(2)-transformed NAb was 6, which indicated that NAb levels could identify breakthrough infected individuals in the vaccinated population. Conclusion: Our study demonstrates that the NAb titers of Omicron BA.2 variant breakthrough cases are higher than in the post-immunized group. The difference in NAb levels could be used to identify cases of breakthrough infection from the post-immunized population in an outbreak epidemic.

Impact of vaccination on kinetics of neutralizing antibodies against SARS-CoV-2 by Serum live neutralization test based on a prospective cohort.

How much the vaccine contributes to the induction and development of neutralizing antibodies (NAbs) of breakthrough cases relative to those unvaccinated-infected cases is not fully understood. We conducted a prospective cohort study and collected serum samples from 576 individuals who were diagnosed with SARS-CoV-2 Delta strain infection, including 245 breakthrough cases and 331 unvaccinated-infected cases. NAbs were analyzed by live virus microneutralization test and transformation of NAb titer. NAbs titers against SARS-CoV-2 ancestral and Delta variant in breakthrough cases were 7.8-fold and 4.0-fold higher than in unvaccinated-infected cases, respectively. NAbs titers in breakthrough cases peaked at the second week after onset/infection. However, the NAbs titers in the unvaccinated-infected cases reached their highest levels during the third week. Compared to those with higher levels of NAbs, those with lower levels of NAbs had no difference in viral clearance duration time (P>0.05), did exhibit higher viral load at the beginning of infection/maximum viral load of infection. NAb levels were statistically higher in the moderate cases than in the mild cases (P<0.0001). Notably, in breakthrough cases, NAb levels were highest longer than 4 months after vaccination (Delta strain: 53118.2 U/mL), and lowest in breakthrough cases shorter than 1 month (Delta strain: 7551.2 U/mL). Cross-neutralization against the ancestral strain and the current circulating isolate (Omicron BA.5) was significantly lower than against the Delta variant in both breakthrough cases and unvaccinated-infected cases. Our study demonstrated that vaccination could induce immune responses more rapidly and greater which could be effective in controlling SARS-CoV-2.

Understanding Drivers of Vaccine Hesitancy During the COVID-19 Pandemic Among Older Adults in Jiangsu Province, China: Cross-sectional Survey.

BACKGROUND: Older adults are particularly at risk from infectious diseases, including serve complications, hospitalization, and death. OBJECTIVE: This study aimed to explore the drivers of vaccine hesitancy among older adults based on the "3Cs" (confidence, complacency, and convenience) framework, where socioeconomic status and vaccination history played the role of moderators. METHODS: A cross-sectional questionnaire survey was conducted in Jiangsu Province, China, between June 1 and July 20, 2021. Older adults (aged ≥60 years) were recruited using a stratified sampling method. Vaccine hesitancy was influenced by the 3Cs in the model. Socioeconomic status and vaccination history processed through the item parceling method were used to moderate associations between the 3Cs and hesitancy. Hierarchical regression analyses and structural equation modeling were used to test the validity of the new framework. We performed 5000 trials of bootstrapping to calculate the 95% CI of the pathway's coefficients. RESULTS: A total of 1341 older adults participated. The mean age was 71.3 (SD 5.4) years, and 44.7% (599/1341) of participants were men. Confidence (b=0.967; 95% CI 0.759-1.201; P=.002), convenience (b=0.458; 95% CI 0.333-0.590; P=.002), and less complacency (b=0.301; 95% CI 0.187-0.408; P=.002) were positively associated with less vaccine hesitancy. Socioeconomic status weakened the positive effect of low complacency (b=-0.065; P=.03) on low vaccine hesitancy. COVID-19 vaccination history negatively moderated the positive association between confidence (b=-0.071; P=.02) and lower vaccine hesitancy. CONCLUSIONS: Our study identified that confidence was the more influential dimension in reducing vaccine hesitancy among older adults. COVID-19 vaccination history, as well as confidence, had a positive association with less vaccine hesitancy and could weaken the role of confidence in vaccine hesitancy. Socioeconomic status had a substitution relationship with less complacency, which suggested a competitive positive association between them on less vaccine hesitancy.

Development of a multiplex RT-PCR method for the detection of four porcine enteric coronaviruses.

Porcine enteric coronaviruses are pathogens that cause viral diarrhea in pigs and are widely prevalent worldwide. Moreover, studies have shown that some porcine enteric coronaviruses can infect humans and poultry. In order to effectively monitor these viruses, it is necessary to establish a multiple detection method to understand their prevalence and conduct in-depth research. Common porcine enteric coronaviruses include Porcine epidemic diarrhea virus (PEDV), Porcine transmissible gastroenteritis virus (TGEV), Porcine delta coronavirus (PDCoV), and Swine acute diarrhea syndrome coronavirus (SADS-CoV). Pigs infected with these viruses have the common clinical symptoms that are difficult to distinguish. A quadruplex RT-PCR (reverse transcription-polymerase chain reaction) method for the simultaneous detection of PEDV, PDCoV, TGEV and SADS-CoV was developed. Four pairs of specific primers were designed for the PEDV M gene, PDCoV N gene, TGEV S gene and SADS-CoV RdRp gene. Multiplex RT-PCR results showed that the target fragments of PDCoV, SADS-CoV, PEDV and TGEV could be amplified by this method. and the specific fragments with sizes of 250 bp, 368 bp, 616 bp and 801 bp were amplified, respectively. This method cannot amplify any fragment of nucleic acids of Seneca Valley virus (SVV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Atypical Porcine Pestivirus (APPV), and has good specificity. The lowest detection limits of PDCoV, PEDV, TGEV and SADS-CoV were 5.66 × 105 copies/µL, 6.48 × 105 copies/µL, 8.54 × 105 copies/µL and 7.79 × 106 copies/µL, respectively. A total of 94 samples were collected from pig farms were analyzed using this method. There were 15 positive samples for PEDV, 3 positive samples for mixed infection of PEDV and PDCoV, 2 positive samples for mixed infection of PEDV and TGEV, and 1 positive sample for mixed infection of PEDV, TGEV, and PDCoV. Multiplex RT-PCR method could detect four intestinal coronaviruses (PEDV, PDCoV, TGEV, and SADS-CoV) in pigs efficiently, cheaply and accurately, which can be used for clinical large-scale epidemiological investigation and diagnosis.

Six-month follow-up of a booster dose of CoronaVac in two single-centre phase 2 clinical trials.

Determining the duration of immunity induced by booster doses of CoronaVac is crucial for informing recommendations for booster regimens and adjusting immunization strategies. In two single-centre, double-blind, randomised, placebo-controlled phase 2 clinical trials, immunogenicity and safety of four immunization regimens are assessed in adults aged 18 to 59 years and one immunization regimen in adults aged 60 years and older, respectively. Serious adverse events occurring within 6 months after booster doses are recorded as pre-specified secondary endpoints, geometric mean titres (GMTs) of neutralising antibodies one year after the 3-dose schedule immunization and 6 months after the booster doses are assessed as pre-specified exploratory endpoints, GMT fold-decreases in neutralization titres are assessed as post-hoc analyses. Neutralising antibody titres decline approximately 4-fold and 2.5-fold from day 28 to day 180 after third doses in adults aged 18-59 years of age and in adults aged 60 years and older, respectively. No safety concerns are identified during the follow-up period. There are increases in the magnitude and duration of humoral response with homologous booster doses of CoronaVac given 8 months after a primary two-dose immunization series, which could prolong protection and contribute to building our wall of population immunity. Trial number: NCT04352608 and NCT04383574.

Long-Term Kinetics of SARS-CoV-2 Antibodies and Impact of Inactivated Vaccine on SARS-CoV-2 Antibodies Based on a COVID-19 Patients Cohort.

Background: Understanding the long-term kinetic characteristics of SARS-CoV-2 antibodies and the impact of inactivated vaccines on SARS-CoV-2 antibodies in convalescent patients can provide information for developing and improving vaccination strategies in such populations. Methods: In this cohort, 402 convalescent patients who tested positive for SARS-CoV-2 by RT-PCR from 1 January to 22 June 2020 in Jiangsu, China, were enrolled. The epidemiological data included demographics, symptom onset, and vaccination history. Blood samples were collected and tested for antibody levels of specific IgG, IgM, RBD-IgG, S-IgG, and neutralizing antibodies using a the commercial magnetic chemiluminescence enzyme immunoassay. Results: The median follow-up time after symptom onset was 15.6 months (IQR, 14.6 to 15.8). Of the 402 convalescent patients, 44 (13.84%) received an inactivated vaccine against COVID-19. A total of 255 (80.19%) patients were IgG-positive and 65 (20.44%) were IgM-positive. The neutralizing antibody was 83.02%. Compared with non-vaccinated individuals, the IgG antibody levels in vaccinated people were higher (P=0.007). Similarly, antibody levels for RBD-IgG, S-IgG, and neutralizing antibodies were all highly increased in vaccinated individuals (P<0.05). IgG levels were significantly higher after vaccination than before vaccination in the same population. IgG levels in those who received 'single dose and ≥14d' were similar to those with two doses (P>0.05). Similar conclusions were drawn for RBD-IgG and the neutralizing antibody. Conclusion: 15.6 months after symptom onset, the majority of participants remained positive for serum-specific IgG, RBD-IgG, S-IgG, and neutralizing antibodies. For convalescent patients, a single dose of inactivated vaccine against COVID-19 can further boost antibody titres.

Epidemiologic characteristics and influencing factors of cluster infection of COVID-19 in Jiangsu Province.

To understand the characteristics and influencing factors related to cluster infections in Jiangsu Province, China, we investigated case reports to explore transmission dynamics and influencing factors of scales of cluster infection. The effectiveness of interventions was assessed by changes in the time-dependent reproductive number (Rt). From 25th January to 29th February, Jiangsu Province reported a total of 134 clusters involving 617 cases. Household clusters accounted for 79.85% of the total. The time interval from onset to report of index cases was 8 days, which was longer than that of secondary cases (4 days) (χ2 = 22.763, P < 0.001) and had a relationship with the number of secondary cases (the correlation coefficient (r) = 0.193, P = 0.040). The average interval from onset to report was different between family cluster cases (4 days) and community cluster cases (7 days) (χ2 = 28.072, P < 0.001). The average time interval from onset to isolation of patients with secondary infection (5 days) was longer than that of patients without secondary infection (3 days) (F = 9.761, P = 0.002). Asymptomatic patients and non-familial clusters had impacts on the size of the clusters. The average reduction in the Rt value in family clusters (26.00%, 0.26 ± 0.22) was lower than that in other clusters (37.00%, 0.37 ± 0.26) (F = 4.400, P = 0.039). Early detection of asymptomatic patients and early reports of non-family clusters can effectively weaken cluster infections.

Chinese Residents' Perceptions of COVID-19 During the Pandemic: Online Cross-sectional Survey Study.

BACKGROUND: COVID-19 has posed a global threat due to substantial morbidity and mortality, and health education strategies need to be adjusted accordingly to prevent a possible epidemic rebound. OBJECTIVE: This study aimed to evaluate the perceptions of COVID-19 among individuals coming to, returning to, or living in Jiangsu Province, China, and determine the impact of the pandemic on the perceptions of the public. METHODS: In this study, an online questionnaire was distributed to participants between February 15 and April 21, 2020. The questionnaire comprised items on personal information (eg, sex, age, educational level, and occupation); protection knowledge, skills, and behaviors related to COVID-19; access to COVID-19-related information; and current information needs. Factors influencing the knowledge score, skill score, behavior score, and total score for COVID-19 were evaluated using univariate and multivariate analyses. The time-varying reproduction number (Rt) and its 95% credible interval were calculated and compared with the daily participation number and protection scores. RESULTS: In total, 52,066 participants were included in the study; their average knowledge score, skill score, behavior score, and total score were 25.58 (SD 4.22), 24.05 (SD 4.02), 31.51 (SD 2.84), and 90.02 (SD 8.87), respectively, and 65.91% (34,315/52,066) had a total protection score above 90 points. For the knowledge and skill sections, correct rates of answers to questions on medical observation days, infectiousness of asymptomatic individuals, cough or sneeze treatment, and precautions were higher than 95%, while those of questions on initial symptoms (32,286/52,066, 62.01%), transmission routes (37,134/52,066, 71.32%), selection of disinfection products (37,390/52,066, 71.81%), and measures of home quarantine (40,037/52,066, 76.90%) were relatively low. For the actual behavior section, 97.93% (50,989/52,066) of participants could wear masks properly when going out. However, 19.76% (10,290/52,066) could not disinfect their homes each week, and 18.42% (9589/52,066) could not distinguish differences in initial symptoms between the common cold and COVID-19. The regression analyses showed that the knowledge score, skill score, behavior score, and total score were influenced by sex, age, educational level, occupation, and place of residence at different degrees (P<.001). The government, television shows, and news outlets were the main sources of protection knowledge, and the information released by the government and authoritative medical experts was considered the most reliable. The current information needs included the latest epidemic developments, disease treatment progress, and daily protection knowledge. The Rt in the Jiangsu Province and mainland China dropped below 1, while the global Rt remained at around 1. The maximal information coefficients ranged from 0.76 to 1.00, which indicated that the public's perceptions were significantly associated with the epidemic. CONCLUSIONS: A high proportion of the participants had sufficient COVID-19 protection knowledge and skills and were able to avoid risky behaviors. Thus, it is necessary to apply different health education measures tailored to work and study resumption for specific populations to improve their self-protection and, ultimately, to prevent a possible rebound of COVID-19.

Two-Pool Multiplex Long-Amplicon Amplification and Full-Genome Sequencing of SARS-CoV-2 (preprint)

BackgroundSince the first public genome of SARS-CoV-2, over 170,000 genome sequences of the virus have been shared by researchers world-wide (till November 1st 2020). Multiplex PCR targeting SARS-CoV-2 followed by massively parallel sequencing (MPS) and/or nanopore sequencing is a widely used strategy to recover the genome from primary samples. However, the bias of amplification among different amplicons should not be ignored, which might lead to uneven sequencing coverage on the viral genome.MethodsWe aim to develop a novel multiplex PCR panel to achieve an improved coverage evenness of SARS-CoV-2. We adapt long amplicons (~1000-bp) for the panel and thus reduced the number of primer pairs. The panel was validated with clinical samples and sequenced via MPS sequencing systems and a portable nanopore sequencing device MinION. We evaluated the full-genome coverage evenness and its dependence on viral loads of the long amplicon panel; we then compared it with a 98-plex panel provided by the ARTIC network. The accuracy to identify viral genomic variations based on the panel and sequencing with MinION was assessed.ResultsWe developed a two-pool 36-plex panel for full-genome sequencing of SARS-CoV-2, whose amplicon size ranged from 880 to 1027 bp. For samples with a <30 Ct value, >90% viral genome could be recovered with a high sequencing depth (>0.2 mean depth) by using the long-amplicon panel (n = 36), compared with 79-88% highly covered genome region for the ARTIC panel (n = 5). The coverage evenness of the long-amplicon panel was also less affected by low viral titers and not dependent on sequencing data amount. With MinION sequencing, the consensus viral genomes could be reliably recovered. However, a high false positive rate was observed to identify sub-clonal genomic variations with a <0.6 frequency.ConclusionA novel multiplex PCR panel for full-genome sequencing of SARS-CoV-2 with improved coverage evenness and low requirement of data throughput was validated with clinical samples. Amplification of SARS-CoV-2 with the panel followed by MinION sequencing could generate reliable consensus genome sequences, but the detection of non-dominating viral populations within host is error-prone.

Genomic Elucidation of a COVID-19 Resurgence and Local Transmission of SARS-CoV-2 in Guangzhou, China (preprint)

The resurgence of coronavirus disease 2019 (COVID-19) has been seen in many counties where outbreaks appear to be leveling off. While China experienced a dramatic decline of COVID-19 at the outset of 2020, regional outbreaks continuously emerged in recent months. In Guangzhou, a small outbreak emerged in March and April involving less than 100 residents, and a comprehensive and near-real-time genomic surveillance of SARS-CoV-2 was conducted. When confirmed cases among overseas travelers increased, public health authorities enhanced measures as shifting self-quarantine to central quarantine and SARS-CoV-2 testing for all overseas travelers. From 109 imported cases we found diverse viral variants distributing in the global viral phylogeny, which were usually shared within households but not among passengers on the same flight. Nonetheless, local transmission was predominately attributed to two specific variants imported from Africa, including the local cases who reported no direct/indirect contact with imported cases. The introducing events of the virus were identified or deduced before enhanced measures were taken. These results show that the interventions are effective in containing the spread of SARS-CoV-2, and also rule out the possibility of cryptic transmission of viral variants from the first wave in January and February. Moreover, we found that intra-host viral diversity was usually different between close contacts, implying a transmission bottleneck of SARS-CoV-2. Our study provides evidence and emphasizes the importance of controls for oversea travelers in the context of the pandemic, and exemplifies how viral genomic data facilitates COVID-19 surveillance and prevention.Funding: This study was supported by National Natural Science Foundation of China (31870079, 91953122, 31871326), National Science and Technology Major Project of the Ministry of Science and Technology of China (2017ZX10103011, 2018ZX10305410, 2018ZX10201001), Guangdong Provincial Novel Coronavirus Scientific and Technological Project (2020111107001), Guangdong Basic and Applied Basic Research Foundation (2020A1515010776 and 2020B1515020057) and the Beijing Nova Program (Z181100006218114 and Z181100006218110) to M.N. and P.L..Conflict of Interest: The authors declare no competing interests.Ethical Approval: This study was approved by the ethics committee of the Center for Disease Control and Prevention (CDC) of Guangzhou (GZCDC-ECHR-2020P0002). Written informed consent was obtained from patients about the surveillance and data related to disease control and further analysis. All information regarding individual persons has been anonymized in this study.

Management in the paediatric wards facing novel coronavirus infection: a rapid review of guidelines and consensuses.

OBJECTIVES: Relevant guidelines and consensuses for COVID-19 contain recommendations aimed at optimising the management in paediatric wards. The goal of this study was to determine the quality of those recommendations and provide suggestions to hospital managers for the adjustment of existing hospital prevention and control strategies, and also to offer recommendations for further research. DESIGN: A rapid review of the guidelines and consensuses for the management in paediatric wards facing COVID-19. METHODS: PubMed, EMBASE, the Cochrane Library, UpToDate, China National Knowledge Infrastructure, the Wanfang database and relevant websites such as medlive.cn, dxy.cn, the National Health and Health Commission and the China Center for Disease Control and Prevention were systematically searched through late May 2020. The Appraisal of Guidelines for Research and Evaluation II (AGREE II) tool was then used to assess the quality of the selected articles and summarise the relevant evidence concerning management in paediatric wards. RESULTS: A total of 35 articles were included, composed of 3 consensus guidelines, 25 expert consensuses and 7 expert opinions. Of the 35 papers, 24 were from China, 2 from the USA, 1 from Spain, 1 from Brazil, 1 from Saudi Arabia and 6 from multinational cooperative studies. Scores for the six domains of the AGREE II tool (scope and purpose, stakeholder involvement, rigour of development, clarity of presentation, applicability and editorial independence) were 98.57%, 53.57%, 17.92%, 69.62%, 26.96% and 50.35%, respectively. Recommendations for nosocomial infection and control, human resource management as well as management of paediatric patients and their families were summarised. CONCLUSIONS: Due to the outbreak of COVID-19, the quality of rapid guidelines and consensuses for the management in paediatric wards affected by COVID-19 is unsatisfactory. In the future, it will be necessary to develop more high-quality guidelines or consensuses for the management in paediatric wards to deal with nosocomial outbreaks in order to fully prepare for emergency medical and health problems.

COVID-19 outbreak following a single patient exposure at an entertainment site: An epidemiological study.

We investigated an outbreak of COVID-19 infection, which was traced back to a bathing pool at an entertainment venue, to explore the epidemiology of the outbreak, understand the transmissibility of the virus and analyse the influencing factors. Contact investigation and management were conducted to identify potential cases. Epidemiological investigation was carried out to determine the epidemiological and demographic characteristics of the outbreak. We estimated the secondary attack rate (SAR), incubation time and time-dependent reproductive number (Rt ) and explored the predisposing factors for cluster infection. The incubation time was 5.4 days and the serial interval (SI) was 4.4 days, with the rate of negative-valued SIs at 24.5%. The SAR at the bathing pool (3.3%) was relatively low due to its high temperature and humidity. The SAR was higher in the colleagues' cluster (20.5%) than in the family cluster (11.8%). Super-spreaders had a longer isolation delay time (p = .004). The Rt of the cluster decreased from the highest value of 3.88 on January 27, 2020 to 1.22 on February 6. Our findings suggest that the predisposing factors of the outbreak included close contact with an infected person, airtight and crowded spaces, temperature and humidity in the space and untimely isolation of patients and quarantine of contacts at the early stage of transmission. Measures to reduce the risk of infection at these gatherings and subsequent tracking of close contacts were effective.

Genomic surveillance of a resurgence of COVID-19 in Guangzhou, China (preprint)

In the middle of March, the World Health Organization declared the outbreak of COVID-19 caused by SARS-CoV-2 infection a global pandemic. While China experienced a dramatic decline in daily growth rate of COVID-19, multiple importations of new cases from other countries and their related local infections caused a rapid rise. Between March 12 and April 15, we collected nasopharyngeal samples from 109 imported cases from 25 countries and 69 local cases in Guangzhou, China. In order to characterize the transmission patterns and genetic evolution of this virus among different populations, we sequenced the genome of SARS-CoV-2. The imported viral strains were assigned to lineages distributed in Europe (33.0%), America (17.4%), Africa (25.7%), or Southeast/West Asia (23.9%). Importantly, 10 imported cases from Africa formed two novel sub-lineages not identified in global tree previously. A detailed analysis showed that the imported viral strains from Philippines and Pakistan were closely related and within the same sub-lineage, whereas Ethiopia had varied lineages in the African phylogenetic tree. In spite of the diversity of imported SARS-CoV-2, 60 of 69 local infections could be traced back to two specific small lineages imported from Africa. A combined genetic and epidemiological analysis revealed a high-resolution transmission network of the imported SARS-CoV-2 in local communities, which might help inform the public health response and genomic surveillance in other cities and regions. Finally, we observed in-frame deletions on seven loci of SARS-CoV-2 genome, some of which were intra-host mutations, and they exhibited no enrichment on the S protein. Our findings provide new insight into the viral phylodynamics of SARS-CoV-2 and beta coronavirus.