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1.
JMIR Public Health Surveill ; 7(6): e26784, 2021 06 01.
Article in English | MEDLINE | ID: covidwho-2197902

ABSTRACT

BACKGROUND: Despite recent achievements in vaccines, antiviral drugs, and medical infrastructure, the emergence of COVID-19 has posed a serious threat to humans worldwide. Most countries are well connected on a global scale, making it nearly impossible to implement perfect and prompt mitigation strategies for infectious disease outbreaks. In particular, due to the explosive growth of international travel, the complex network of human mobility enabled the rapid spread of COVID-19 globally. OBJECTIVE: South Korea was one of the earliest countries to be affected by COVID-19. In the absence of vaccines and treatments, South Korea has implemented and maintained stringent interventions, such as large-scale epidemiological investigations, rapid diagnosis, social distancing, and prompt clinical classification of severely ill patients with appropriate medical measures. In particular, South Korea has implemented effective airport screenings and quarantine measures. In this study, we aimed to assess the country-specific importation risk of COVID-19 and investigate its impact on the local transmission of COVID-19. METHODS: The country-specific importation risk of COVID-19 in South Korea was assessed. We investigated the relationships between country-specific imported cases, passenger numbers, and the severity of country-specific COVID-19 prevalence from January to October 2020. We assessed the country-specific risk by incorporating country-specific information. A renewal mathematical model was employed, considering both imported and local cases of COVID-19 in South Korea. Furthermore, we estimated the basic and effective reproduction numbers. RESULTS: The risk of importation from China was highest between January and February 2020, while that from North America (the United States and Canada) was high from April to October 2020. The R0 was estimated at 1.87 (95% CI 1.47-2.34), using the rate of α=0.07 for secondary transmission caused by imported cases. The Rt was estimated in South Korea and in both Seoul and Gyeonggi. CONCLUSIONS: A statistical model accounting for imported and locally transmitted cases was employed to estimate R0 and Rt. Our results indicated that the prompt implementation of airport screening measures (contact tracing with case isolation and quarantine) successfully reduced local transmission caused by imported cases despite passengers arriving from high-risk countries throughout the year. Moreover, various mitigation interventions, including social distancing and travel restrictions within South Korea, have been effectively implemented to reduce the spread of local cases in South Korea.


Subject(s)
COVID-19/epidemiology , COVID-19/transmission , Communicable Diseases, Imported/epidemiology , Humans , Models, Statistical , Republic of Korea/epidemiology , Risk Assessment
2.
Euro Surveill ; 27(43)2022 10.
Article in English | MEDLINE | ID: covidwho-2154580

ABSTRACT

BackgroundTracking person-to-person SARS-CoV-2 transmission in the population is important to understand the epidemiology of community transmission and may contribute to the containment of SARS-CoV-2. Neither contact tracing nor genomic surveillance alone, however, are typically sufficient to achieve this objective.AimWe demonstrate the successful application of the integrated genomic surveillance (IGS) system of the German city of Düsseldorf for tracing SARS-CoV-2 transmission chains in the population as well as detecting and investigating travel-associated SARS-CoV-2 infection clusters.MethodsGenomic surveillance, phylogenetic analysis, and structured case interviews were integrated to elucidate two genetically defined clusters of SARS-CoV-2 isolates detected by IGS in Düsseldorf in July 2021.ResultsCluster 1 (n = 67 Düsseldorf cases) and Cluster 2 (n = 36) were detected in a surveillance dataset of 518 high-quality SARS-CoV-2 genomes from Düsseldorf (53% of total cases, sampled mid-June to July 2021). Cluster 1 could be traced back to a complex pattern of transmission in nightlife venues following a putative importation by a SARS-CoV-2-infected return traveller (IP) in late June; 28 SARS-CoV-2 cases could be epidemiologically directly linked to IP. Supported by viral genome data from Spain, Cluster 2 was shown to represent multiple independent introduction events of a viral strain circulating in Catalonia and other European countries, followed by diffuse community transmission in Düsseldorf.ConclusionIGS enabled high-resolution tracing of SARS-CoV-2 transmission in an internationally connected city during community transmission and provided infection chain-level evidence of the downstream propagation of travel-imported SARS-CoV-2 cases.


Subject(s)
COVID-19 , Communicable Diseases, Imported , Humans , SARS-CoV-2/genetics , Travel , Communicable Diseases, Imported/epidemiology , COVID-19/epidemiology , Phylogeny , Contact Tracing , Germany/epidemiology , Genomics
3.
JMIR Public Health Surveill ; 7(9): e30406, 2021 09 01.
Article in English | MEDLINE | ID: covidwho-2141343

ABSTRACT

BACKGROUND: Data on how SARS-CoV-2 enters and spreads in a population are essential for guiding public policies. OBJECTIVE: This study seeks to understand the transmission dynamics of SARS-CoV-2 in small Brazilian towns during the early phase of the epidemic and to identify core groups that can serve as the initial source of infection as well as factors associated with a higher risk of COVID-19. METHODS: Two population-based seroprevalence studies, one household survey, and a case-control study were conducted in two small towns in southeastern Brazil between May and June 2020. In the population-based studies, 400 people were evaluated in each town; there were 40 homes in the household survey, and 95 cases and 393 controls in the case-control study. SARS-CoV-2 serology testing was performed on participants, and a questionnaire was applied. Prevalence, household secondary infection rate, and factors associated with infection were assessed. Odds ratios (ORs) were calculated by logistic regression. Logistics worker was defined as an individual with an occupation focused on the transportation of people or goods and whose job involves traveling outside the town of residence at least once a week. RESULTS: Higher seroprevalence of SARS-CoV-2 was observed in the town with a greater proportion of logistics workers. The secondary household infection rate was 49.1% (55/112), and it was observed that in most households (28/40, 70%) the index case was a logistics worker. The case-control study revealed that being a logistics worker (OR 18.0, 95% CI 8.4-38.7) or living with one (OR 6.9, 95% CI 3.3-14.5) increases the risk of infection. In addition, having close contact with a confirmed case (OR 13.4, 95% CI 6.6-27.3) and living with more than four people (OR 2.7, 95% CI 1.1-7.1) were also risk factors. CONCLUSIONS: Our study shows a strong association between logistics workers and the risk of SARS-CoV-2 infection and highlights the key role of these workers in the viral spread in small towns. These findings indicate the need to focus on this population to determine COVID-19 prevention and control strategies, including vaccination and sentinel genomic surveillance.


Subject(s)
COVID-19/epidemiology , COVID-19/transmission , Communicable Diseases, Imported/epidemiology , Occupations/statistics & numerical data , Transportation/statistics & numerical data , Adolescent , Adult , Brazil/epidemiology , Case-Control Studies , Child , Child, Preschool , Cities/epidemiology , Family Characteristics , Female , Humans , Infant , Infant, Newborn , Male , Middle Aged , Risk Factors , Seroepidemiologic Studies , Young Adult
4.
Global Health ; 17(1): 93, 2021 Aug 21.
Article in English | MEDLINE | ID: covidwho-2098356

ABSTRACT

International air travel has been highlighted as a concern since the beginning of the COVID-19 pandemic with respect to importation of cases. We summarise the available evidence for in-flight transmission of wild type SARS-CoV-2 during 2020, and for imported COVID-19 clusters to cause outbreaks. This paper provides a data baseline prior to the emergence of new mutations causing SARS-CoV-2 variants of concern, whose characteristics may increase the potential risk of in-flight transmission and imported outbreaks. The evidence on in-flight transmission of wild-type SARS-CoV-2 is limited, and is described in a small number of published reports. Most of the available evidence pertains to the early phase of the COVID-19 pandemic, during a period without non-pharmaceutical interventions such as distancing and in-flight mask wearing. There is considerable potential for outbreaks of COVID-19 from imported cases or clusters when public health guidance around quarantine of travellers and self-isolation of cases is not adhered to. Risks can be mitigated by measures such as: avoiding non-essential travel, targeted testing and quarantine of travellers from high incidence regions or regions of concern, managed quarantine processes, and protocols for rapid investigation and control of transmission from a possible variant of concern. Measures should be dynamically assessed and proportionate to the level of risk.


Subject(s)
Air Travel , COVID-19/transmission , COVID-19/virology , Communicable Diseases, Imported/epidemiology , Disease Outbreaks , COVID-19/epidemiology , Humans , SARS-CoV-2/genetics
6.
Pediatr Infect Dis J ; 41(7): e275-e282, 2022 07 01.
Article in English | MEDLINE | ID: covidwho-1788552

ABSTRACT

We aimed to describe the historical perspectives and the current epidemiology of tropical, imported and local endemic infectious diseases in Japan in this review. Public health legislation for infectious diseases and immigration statistics were overviewed to provide the background of the infectious disease situation in Japan. Many tropical diseases were successfully controlled and eliminated in the latter half of the 20th century and the majority of those diseases are imported today. The trend of the main 15 imported infectious diseases before the advent of COVID-19 was summarized as well as local endemic infectious diseases in Japan. Transmission risks of traditional cuisines, lifestyles and nature exposures in Japan are introduced to guide clinicians for travel advice to prevent those local infectious diseases.


Subject(s)
COVID-19 , Communicable Diseases, Imported , Communicable Diseases , COVID-19/epidemiology , Communicable Diseases/epidemiology , Communicable Diseases, Imported/epidemiology , Communicable Diseases, Imported/prevention & control , Humans , Japan/epidemiology , Travel
9.
Nat Commun ; 13(1): 1012, 2022 02 23.
Article in English | MEDLINE | ID: covidwho-1709629

ABSTRACT

Mitigation of SARS-CoV-2 transmission from international travel is a priority. We evaluated the effectiveness of travellers being required to quarantine for 14-days on return to England in Summer 2020. We identified 4,207 travel-related SARS-CoV-2 cases and their contacts, and identified 827 associated SARS-CoV-2 genomes. Overall, quarantine was associated with a lower rate of contacts, and the impact of quarantine was greatest in the 16-20 age-group. 186 SARS-CoV-2 genomes were sufficiently unique to identify travel-related clusters. Fewer genomically-linked cases were observed for index cases who returned from countries with quarantine requirement compared to countries with no quarantine requirement. This difference was explained by fewer importation events per identified genome for these cases, as opposed to fewer onward contacts per case. Overall, our study demonstrates that a 14-day quarantine period reduces, but does not completely eliminate, the onward transmission of imported cases, mainly by dissuading travel to countries with a quarantine requirement.


Subject(s)
COVID-19/prevention & control , Communicable Diseases, Imported/prevention & control , Quarantine/legislation & jurisprudence , SARS-CoV-2/genetics , COVID-19/epidemiology , COVID-19/transmission , Communicable Diseases, Imported/epidemiology , Communicable Diseases, Imported/transmission , Contact Tracing , England/epidemiology , Genome, Viral/genetics , Genomics , Health Impact Assessment , Humans , SARS-CoV-2/classification , Travel/legislation & jurisprudence , Travel-Related Illness
10.
J Infect Dev Ctries ; 15(12): 1792-1800, 2021 12 31.
Article in English | MEDLINE | ID: covidwho-1638107

ABSTRACT

INTRODUCTION: The novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), etiological agent of coronavirus disease 2019 (COVID-19) was first reported in China in December 2019 and spread worldwide. As of March 6th, 2021, there have been 116,670,105 million confirmed cases globally including 2,592,085 deaths. COVID-19 cases have been reported in 219 countries and territories, creating global panic. Mozambique has witnessed the evolution of COVID-19 epidemic associated with the weakness of health system, mostly in terms of laboratory diagnosis capacity, concerns on compliance to effective public health measures including physical distancing, use of masks in crowded indoor areas, hand hygiene, isolation and quarantine of people. METHODOLOGY: The data included in this study were collected from published articles regarding COVID-19 imported cases and severity in Africa, especially in Mozambique. Additionally, official documents of COVID-19 epidemiology from Minister of Health and National Institute of Health of Mozambique from 22nd of March 2020 to 1st of August 2020 were included. RESULTS: The SARS-CoV-2 strains imported mainly from South Africa and European countries might have been playing an important role on COVID-19 epidemic evolution in Mozambique. CONCLUSIONS: These circulating strains in the country, might be similar enough to the strains found in other countries, yet the genomic characterization is needed particularly during the phase of borders reopening through understanding the source of infections and guiding the implementation of containment and mitigation measures in the country.


Subject(s)
COVID-19/epidemiology , Communicable Diseases, Imported/epidemiology , Africa/epidemiology , Female , Global Health , Humans , Male , Mozambique/epidemiology , Pandemics , Patient Acuity , SARS-CoV-2
11.
Cochrane Database Syst Rev ; 10: CD013717, 2020 10 05.
Article in English | MEDLINE | ID: covidwho-1557155

ABSTRACT

BACKGROUND: In late 2019, first cases of coronavirus disease 2019, or COVID-19, caused by the novel coronavirus SARS-CoV-2, were reported in Wuhan, China. Subsequently COVID-19 spread rapidly around the world. To contain the ensuing pandemic, numerous countries have implemented control measures related to international travel, including border closures, partial travel restrictions, entry or exit screening, and quarantine of travellers. OBJECTIVES: To assess the effectiveness of travel-related control measures during the COVID-19 pandemic on infectious disease and screening-related outcomes. SEARCH METHODS: We searched MEDLINE, Embase and COVID-19-specific databases, including the WHO Global Database on COVID-19 Research, the Cochrane COVID-19 Study Register, and the CDC COVID-19 Research Database on 26 June 2020. We also conducted backward-citation searches with existing reviews. SELECTION CRITERIA: We considered experimental, quasi-experimental, observational and modelling studies assessing the effects of travel-related control measures affecting human travel across national borders during the COVID-19 pandemic. We also included studies concerned with severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) as indirect evidence. Primary outcomes were cases avoided, cases detected and a shift in epidemic development due to the measures. Secondary outcomes were other infectious disease transmission outcomes, healthcare utilisation, resource requirements and adverse effects if identified in studies assessing at least one primary outcome. DATA COLLECTION AND ANALYSIS: One review author screened titles and abstracts; all excluded abstracts were screened in duplicate. Two review authors independently screened full texts. One review author extracted data, assessed risk of bias and appraised study quality. At least one additional review author checked for correctness of all data reported in the 'Risk of bias' assessment, quality appraisal and data synthesis. For assessing the risk of bias and quality of included studies, we used the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool for observational studies concerned with screening, ROBINS-I for observational ecological studies and a bespoke tool for modelling studies. We synthesised findings narratively. One review author assessed certainty of evidence with GRADE, and the review author team discussed ratings. MAIN RESULTS: We included 40 records reporting on 36 unique studies. We found 17 modelling studies, 7 observational screening studies and one observational ecological study on COVID-19, four modelling and six observational studies on SARS, and one modelling study on SARS and MERS, covering a variety of settings and epidemic stages. Most studies compared travel-related control measures against a counterfactual scenario in which the intervention measure was not implemented. However, some modelling studies described additional comparator scenarios, such as different levels of travel restrictions, or a combination of measures. There were concerns with the quality of many modelling studies and the risk of bias of observational studies. Many modelling studies used potentially inappropriate assumptions about the structure and input parameters of models, and failed to adequately assess uncertainty. Concerns with observational screening studies commonly related to the reference test and the flow of the screening process. Studies on COVID-19 Travel restrictions reducing cross-border travel Eleven studies employed models to simulate a reduction in travel volume; one observational ecological study assessed travel restrictions in response to the COVID-19 pandemic. Very low-certainty evidence from modelling studies suggests that when implemented at the beginning of the outbreak, cross-border travel restrictions may lead to a reduction in the number of new cases of between 26% to 90% (4 studies), the number of deaths (1 study), the time to outbreak of between 2 and 26 days (2 studies), the risk of outbreak of between 1% to 37% (2 studies), and the effective reproduction number (1 modelling and 1 observational ecological study). Low-certainty evidence from modelling studies suggests a reduction in the number of imported or exported cases of between 70% to 81% (5 studies), and in the growth acceleration of epidemic progression (1 study). Screening at borders with or without quarantine Evidence from three modelling studies of entry and exit symptom screening without quarantine suggests delays in the time to outbreak of between 1 to 183 days (very low-certainty evidence) and a detection rate of infected travellers of between 10% to 53% (low-certainty evidence). Six observational studies of entry and exit screening were conducted in specific settings such as evacuation flights and cruise ship outbreaks. Screening approaches varied but followed a similar structure, involving symptom screening of all individuals at departure or upon arrival, followed by quarantine, and different procedures for observation and PCR testing over a period of at least 14 days. The proportion of cases detected ranged from 0% to 91% (depending on the screening approach), and the positive predictive value ranged from 0% to 100% (very low-certainty evidence). The outcomes, however, should be interpreted in relation to both the screening approach used and the prevalence of infection among the travellers screened; for example, symptom-based screening alone generally performed worse than a combination of symptom-based and PCR screening with subsequent observation during quarantine. Quarantine of travellers Evidence from one modelling study simulating a 14-day quarantine suggests a reduction in the number of cases seeded by imported cases; larger reductions were seen with increasing levels of quarantine compliance ranging from 277 to 19 cases with rates of compliance modelled between 70% to 100% (very low-certainty evidence). AUTHORS' CONCLUSIONS: With much of the evidence deriving from modelling studies, notably for travel restrictions reducing cross-border travel and quarantine of travellers, there is a lack of 'real-life' evidence for many of these measures. The certainty of the evidence for most travel-related control measures is very low and the true effects may be substantially different from those reported here. Nevertheless, some travel-related control measures during the COVID-19 pandemic may have a positive impact on infectious disease outcomes. Broadly, travel restrictions may limit the spread of disease across national borders. Entry and exit symptom screening measures on their own are not likely to be effective in detecting a meaningful proportion of cases to prevent seeding new cases within the protected region; combined with subsequent quarantine, observation and PCR testing, the effectiveness is likely to improve. There was insufficient evidence to draw firm conclusions about the effectiveness of travel-related quarantine on its own. Some of the included studies suggest that effects are likely to depend on factors such as the stage of the epidemic, the interconnectedness of countries, local measures undertaken to contain community transmission, and the extent of implementation and adherence.


Subject(s)
COVID-19/prevention & control , Pandemics/prevention & control , SARS-CoV-2 , Travel-Related Illness , COVID-19/epidemiology , Communicable Diseases, Imported/epidemiology , Communicable Diseases, Imported/prevention & control , Coronavirus Infections/epidemiology , Coronavirus Infections/prevention & control , Humans , Models, Theoretical , Observational Studies as Topic , Quarantine , Severe Acute Respiratory Syndrome/epidemiology , Severe Acute Respiratory Syndrome/prevention & control
12.
Emerg Infect Dis ; 27(10): 2666-2668, 2021 10.
Article in English | MEDLINE | ID: covidwho-1486735

ABSTRACT

We sequenced 10% of imported severe acute respiratory syndrome coronavirus 2 infections detected in travelers to Hong Kong and revealed the genomic diversity of regions of origin, including lineages not previously reported from those countries. Our results suggest that international or regional travel hubs might be useful surveillance sites to monitor sequence diversity.


Subject(s)
COVID-19 , Communicable Diseases, Imported , Genetic Variation , Hong Kong/epidemiology , Humans , SARS-CoV-2
14.
Med J Aust ; 216(1): 39-42, 2022 01 17.
Article in English | MEDLINE | ID: covidwho-1463976

ABSTRACT

OBJECTIVE: To estimate the numbers of COVID-19-related hospitalisations in Australia after re-opening the international border. DESIGN: Population-level deterministic compartmental epidemic modelling of eight scenarios applying various assumptions regarding SARS-CoV-2 transmissibility (baseline R0 = 3.5 or 7.0), vaccine rollout speed (slow or fast), and scale of border re-opening (mean of 2500 or 13 000 overseas arrivals per day). SETTING: Simulation population size, age structure, and age-based contact rates based on recent estimates for the Australian population. We assumed that 80% vaccination coverage of people aged 16 years or more was reached in mid-October 2021 (fast rollout) or early January 2022 (slow rollout). MAIN OUTCOME MEASURES: Numbers of people admitted to hospital with COVID-19, December 2021 - December 2022. RESULTS: In scenarios assuming a highly transmissible SARS-CoV-2 variant (R0  = 7.0), opening the international border on either scale was followed by surges in both infections and hospitalisations that would require public health measures beyond mask wearing and social distancing to avoid overwhelming the health system. Reducing the number of hospitalisations to manageable levels required several cycles of additional social and mobility restrictions. CONCLUSIONS: If highly transmissible SARS-CoV-2 variants are circulating locally or overseas, large and disruptive COVID-19 outbreaks will still be possible in Australia after 80% of people aged 16 years or more have been vaccinated. Continuing public health measures to restrict the spread of disease are likely to be necessary throughout 2022.


Subject(s)
COVID-19/epidemiology , Communicable Disease Control/statistics & numerical data , Communicable Diseases, Imported/epidemiology , Disease Outbreaks , Hospitalization/statistics & numerical data , Adolescent , Adult , Aged , Australia/epidemiology , COVID-19/prevention & control , COVID-19/virology , Communicable Disease Control/methods , Communicable Diseases, Imported/virology , Computer Simulation , Female , Humans , Male , Middle Aged , SARS-CoV-2 , Vaccination Coverage/statistics & numerical data , Young Adult
15.
J Travel Med ; 28(7)2021 10 11.
Article in English | MEDLINE | ID: covidwho-1462388

ABSTRACT

BACKGROUND: The COVID-19 pandemic has resulted in the closure or partial closure of international borders in almost all countries. Here, we investigate the efficacy of imported case detection considering quarantine length and different testing measures for travellers on arrival. METHODS: We examine eight broad border control strategies from utilizing quarantine alone, pre-testing, entry and exit testing, and testing during quarantine. In comparing the efficacy of these strategies, we calculate the probability of detecting travellers who have been infected up to 2 weeks pre-departure according to their estimated incubation and infectious period. We estimate the number of undetected infected travellers permitted entry for these strategies across a prevalence range of 0.1-2% per million travellers. RESULTS: At 14-day quarantine, on average 2.2% (range: 0.5-8.2%) of imported infections are missed across the strategies, leading to 22 (5-82) imported cases at 0.1% prevalence per million travellers, increasing up to 430 (106-1641) at 2%. The strategy utilizing exit testing results in 3.9% (3.1-4.9%) of imported cases being missed at 7-day quarantine, down to 0.4% (0.3-0.7%) at 21-day quarantine, and the introduction of daily testing, as the most risk averse strategy, reduces the proportion further to 2.5-4.2% at day 7 and 0.1-0.2% at day 21 dependent on the tests used. Rapid antigen testing every 3 days in quarantine leads to 3% being missed at 7 days and 0.7% at 14 days, which is comparable to PCR testing with a 24-hour turnaround. CONCLUSIONS: Mandatory testing, at a minimal of pre-testing and on arrival, is strongly recommended where the length of quarantining should then be determined by the destination country's level of risk averseness, pandemic preparedness and origin of travellers. Repeated testing during quarantining should also be utilized to mitigate case importation risk and reduce the quarantining duration required.


Subject(s)
COVID-19 , Communicable Diseases, Imported , Communicable Diseases, Imported/epidemiology , Humans , Pandemics , Quarantine , SARS-CoV-2
17.
J Med Virol ; 93(9): 5523-5526, 2021 09.
Article in English | MEDLINE | ID: covidwho-1363692

ABSTRACT

The appearance of new variants of SARS-CoV-2 has recently challenged public health authorities with respect to tracking transmission and mitigating the impact in the evolving pandemic across countries. B.1.525 is considered a variant under investigation since it carries specific genetic signatures present in P.1, B.1.1.7, and B.1.351. Here we report genomic evidence of the first likely imported case of the SARS-CoV-2 B.1.525 variant, isolated in a traveler returning from Nigeria.


Subject(s)
COVID-19/virology , Communicable Diseases, Imported/virology , SARS-CoV-2/genetics , SARS-CoV-2/isolation & purification , Aged , Brazil/epidemiology , COVID-19/diagnosis , COVID-19/epidemiology , Communicable Diseases, Imported/diagnosis , Communicable Diseases, Imported/epidemiology , Female , Genome, Viral/genetics , Humans , Mutation , Nigeria/epidemiology , Travel-Related Illness
18.
Proc Natl Acad Sci U S A ; 118(31)2021 08 03.
Article in English | MEDLINE | ID: covidwho-1319070

ABSTRACT

Since its outbreak in December 2019, the novel coronavirus 2019 (COVID-19) has spread to 191 countries and caused millions of deaths. Many countries have experienced multiple epidemic waves and faced containment pressures from both domestic and international transmission. In this study, we conduct a multiscale geographic analysis of the spread of COVID-19 in a policy-influenced dynamic network to quantify COVID-19 importation risk under different policy scenarios using evidence from China. Our spatial dynamic panel data (SDPD) model explicitly distinguishes the effects of travel flows from the effects of transmissibility within cities, across cities, and across national borders. We find that within-city transmission was the dominant transmission mechanism in China at the beginning of the outbreak and that all domestic transmission mechanisms were muted or significantly weakened before importation posed a threat. We identify effective containment policies by matching the change points of domestic and importation transmissibility parameters to the timing of various interventions. Our simulations suggest that importation risk is limited when domestic transmission is under control, but that cumulative cases would have been almost 13 times higher if domestic transmissibility had resurged to its precontainment level after importation and 32 times higher if domestic transmissibility had remained at its precontainment level since the outbreak. Our findings provide practical insights into infectious disease containment and call for collaborative and coordinated global suppression efforts.


Subject(s)
COVID-19/transmission , Communicable Diseases, Imported/transmission , COVID-19/epidemiology , COVID-19/prevention & control , China/epidemiology , Cities , Communicable Disease Control/legislation & jurisprudence , Communicable Diseases, Imported/epidemiology , Communicable Diseases, Imported/prevention & control , Humans , Models, Statistical , Risk , SARS-CoV-2 , Spatio-Temporal Analysis , Travel
19.
Travel Med Infect Dis ; 44: 102137, 2021.
Article in English | MEDLINE | ID: covidwho-1305318
20.
Lancet Glob Health ; 9(7): e916-e924, 2021 07.
Article in English | MEDLINE | ID: covidwho-1294376

ABSTRACT

BACKGROUND: Vietnam has emerged as one of the world's leading success stories in responding to COVID-19. After a prolonged period of little to no transmission, there was an outbreak of unknown source in July, 2020, in the Da Nang region, but the outbreak was quickly suppressed. We aimed to use epidemiological, behavioural, demographic, and policy data from the COVID-19 outbreak in Da Nang to calibrate an agent-based model of COVID-19 transmission for Vietnam, and to estimate the risk of future outbreaks associated with reopening of international borders in the country. METHODS: For this modelling study, we used comprehensive data from June 15 to Oct 15, 2020, on testing, COVID-19 cases, and quarantine breaches within an agent-based model of SARS-CoV-2 transmission to model a COVID-19 outbreak in Da Nang in July, 2020. We applied this model to quantify the risk of future outbreaks in Vietnam in the 3 months after the reopening of international borders, under different behavioural scenarios, policy responses (ie, closure of workplaces and schools), and ongoing testing. FINDINGS: We estimated that the outbreak in Da Nang between July and August, 2020, resulted in substantial community transmission, and that higher levels of symptomatic testing could have mitigated this transmission. We estimated that the outbreak peaked on Aug 2, 2020, with an estimated 1060 active infections (95% projection interval 890-1280). If the population of Vietnam remains highly compliant with mask-wearing policies, our projections indicate that the epidemic would remain under control even if a small but steady flow of imported infections escaped quarantine into the community. However, if complacency increases and testing rates are relatively low (10% of symptomatic individuals are tested), the epidemic could rebound again, resulting in an estimated 2100 infections (95% projected interval 1050-3610) in 3 months. These outcomes could be mitigated if the behaviour of the general population responds dynamically to increases in locally acquired cases that exceed specific thresholds, but only if testing of symptomatic individuals is also increased. INTERPRETATION: The successful response to COVID-19 in Vietnam could be improved even further with higher levels of symptomatic testing. If the previous approaches are used in response to new COVID-19 outbreaks, epidemic control is possible even in the presence of low levels of imported cases. FUNDING: Ministry of Science and Technology (Vietnam). TRANSLATION: For the Vietnamese translation of the abstract see Supplementary Materials section.


Subject(s)
COVID-19/epidemiology , Communicable Diseases, Imported/epidemiology , Epidemics , Travel/legislation & jurisprudence , Humans , Internationality , Models, Theoretical , Risk Assessment , Vietnam/epidemiology
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