iew ed Title: Sero-prevalence of SARS-CoV-2 in high-risk populations in Vietnam Authors: Tasnim Hasan1,2 MBBS Pham Ngoc Thach3 PhD Nguyen Thu Anh2 PhD pe er re v Le Thi Thu Hien2 MIPH Le Van Duyet3 PhD Dang Thi Thuy3 MD Van Dinh Trang3 PhD Pham Ngoc Yen2 MS Nguyen Viet Ha2 BPharm Tran Linh Giang2 BPharm Nguyen Thi Cam Van2 MD Truong Quang Viet4 MD tn Dao Huu Than4 MD ot Nguyen Trung Thanh2 BSPH Le Thanh Chung5 MD Truong Tan Nam5 MD rin Vo Trung Hoang6 MD Le Thanh Phuc7 MD ep Nguyen Thanh Thao8 MD Luu Van Vinh8 MPH Pr Nguyen Dai Vinh9 MD Brett Toelle1,2,10 PhD Guy B Marks2,11 PhD This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Greg J Fox1,2 PhD 1- Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia 2006 2- The Woolcock Institute of Medical Research, Glebe, NSW, Australia 2037 3- National Hospital of Tropical Diseases, Hanoi, Vietnam 4- Hanoi Center for Disease Control (CDC), Hanoi, Vietnam pe er re v 5- Centre for Disease Control Da Nang, Da Nang City, Vietnam 6- Centre for Disease Control Quang Nam, Quang Nam Province, Vietnam 7- Da Nang Lung Hospital, Da Nang City, Vietnam 8- Quang Nam Pham Ngoc Thach Hospital 9- Hoa Vang District Health Center, Da Nang City, Vietnam 10- Sydney Local Health District, NSW, Australia 11- South Western Sydney Clinical School, The University of New South Wales, Liverpool, NSW, tn Corresponding author: ot Australia Professor Greg Fox rin Room 5216, Level 2, Medical Foundation Building, K26 92-94 Parramatta Road ep The University of Sydney, NSW Australia 2006 Pr Email: greg.fox@sydney.edu.au This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Conflicts of interest: None declared Funding: This project was supported by a grant funded by the Australian Department of Foreign Research Council (APP1153346) Acknowledgements: pe er re v Affairs and Trade, awarded in conjunction with the Australian National Health and Medical We acknowledge the contributions to this study made by healthcare workers from National Hospital for Tropical Diseases, Quang Nam Pham Ngoc Thach Hospital, Da Nang Lung Hospital, Centre for Disease Control in Hanoi, Danang and Quang Nam Provinces and Me Linh, Thang Binh, Dien Ban and Hoa Vang District Health Centers in Vietnam We acknowledge the valuable contributions the research staff of the Woolcock Institute of tn Data sharing: ot Medical Research, Vietnam, and local partners to undertake the serology survey The data used for this research, including deidentified participant data and data dictionary, rin are available from the corresponding author on request ep Author contributions: Tasnim Hasan: manuscript preparation, writing – first draft, writing – editing, data analysis Pham Ngoc Thach: investigation, project administration, writing – review and editing Pr Nguyen Thu Anh: supervision, conceptualisation, data curation, writing - review and editing Le Thi Thu Hien: supervision, data curation, investigation, project administration, writing – review and editing This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Le Van Duyet: investigation, project administration, writing – review and editing Dang Thi Thuy: investigation, project administration, writing – review and editing Van Dinh Trang: investigation, project administration, writing – review and editing Pham Ngoc Yen: investigation, project administration, writing – review and editing Nguyen Viet Ha: data curation, investigation, project administration, writing – review and editing Tran Linh Giang: data curation, investigation, project administration, writing – review and editing pe er re v Nguyen Thi Cam Van: data curation, investigation, project administration, writing – review and editing Nguyen Trung Thanh: data curation, investigation, project administration, writing – review and editing Truong Quang Viet: investigation, project administration, writing – review and editing Dao Huu Than: investigation, project administration, writing – review and editing Le Thanh Chung: investigation, project administration, writing – review and editing Truong Tan Nam: investigation, project administration, writing – review and editing Vo Trung Hoang: investigation, project administration, writing – review and editing ot Le Thanh Phuc: investigation, project administration, writing – review and editing Nguyen Thanh Thao: investigation, project administration, writing – review and editing tn Luu Van Vinh: investigation, project administration, writing – review and editing Nguyen Dai Vinh: investigation, project administration, writing – review and editing Brett Toelle: conceptualisation, supervision, data curation, writing – review and editing rin Guy B Marks: conceptualisation, supervision, writing – review and editing Pr ep Greg J Fox: conceptualisation, supervision, writing – review and editing This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Abstract: Background: As a response to the coronavirus disease 2019 (COVID-19) pandemic, Vietnam enforced strict quarantine, contact tracing and physical distancing policies By December 2020, this strategy resulted in one of the lowest numbers of individuals infected with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) cases globally This risk populations in Vietnam pe er re v study aimed to determine the prevalence of SARS-CoV-2 antibody positivity among high- Methods: A prevalence survey was undertaken within four communities in northern and central Vietnam, where at least two COVID-19 cases had been confirmed Participants were classified according to the location of exposure: household contacts, close contacts, community members, and healthcare workers (HCWs) responsible for treating COVID-19 cases Participants completed a baseline questionnaire that evaluated exposure history SARS-CoV-2 IgG antibodies were quantified using a commercially available assay Results: 3049 community members and 149 health care workers provided consent to ot participate Among enrolled community members, 27 (0·9%) were household contacts and 53 (1·7%) were close contacts Serology was performed in 3034 individuals Among 13 tn individuals who were seropositive (0·4%), five household contacts (5/27, 18·5%), one close contact (1/53, 1·9%), and seven community members (7/2954, 0·2%) had detectable SARS- rin CoV-2 antibodies All HCWs were negative for SARS-CoV-2 antibodies Participants were tested a median of 15·1 (interquartile range 14·9 to 15·2) weeks after exposure ep Conclusion: The presence of SARS-CoV-2 antibodies in high-risk communities and healthcare workers was low in communities in Vietnam with known COVID-19 cases The public health response to the COVID-19 pandemic in Vietnam has been effective in limiting Pr community transmission of SARS-CoV-2 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Research in context Evidence before this study Vietnam is one of the few countries which has effectively controlled the COVID-19 pandemic with very low reported case numbers, mortality However, there is speculation as to whether official figures may underestimate the epidemiological extent of infection in pe er re v Vietnam Sero-prevalence studies is a method which can provide a surrogate measure of the extent of SARS-CoV-2 infection in the general population Although there are several studies looking at the prevalence of SARS-CoV-2 antibodies in populations around the world, no sero-prevelance studies have been performed in the Vietnamese community A limited number of studies which specifically look at prevalence of antibodies in high-risk contacts including household contacts, close contacts and community members The determination of sero-prevalence in high-risk populations in Vietnam can provide an insight into understanding if the strict physical distancing and quarantine policies have been effective in ot controlling community transmission of COVID-19 in Vietnam tn Added value of this study The overall prevalence of SARS-CoV-2 antibodies in high-risk communities was low – just rin 0·4% As expected, household contacts of confirmed COVID-19 cases, had a higher prevalence of antibodies (18·5%), while the prevalence was lower in close contacts (1·9%) ep and members of the general community (0·2%) The absence of sero-positivity among health care workers is unique, with only one other study, also in Vietnam, being able to demonstrate the lack of SARS-CoV-2 antibodies in health care workers who are directly involved in the Pr care of COVID-19 patients The low seroprevalence of SARS-CoV-2 antibodies in high-risk This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Vietnamese populations confirms the effectiveness of rapidly enforced strict policies implemented by the Vietnamese government in controlling the COVID-19 pandemic Implications of all the available evidence This study provides a strong message of the importance of government policies to limit the spread of the COVID-19 pandemic Furthermore, it affirms that control of COVID-19 is Pr ep rin tn ot pe er re v possible, even in a densely populated, moderately-resourced setting This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Introduction Vietnam is a populous southeast Asian country, bordering China By December 2020, the country had reported among the lowest number of cases of infection with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) globally.1 Prompt border closures, quarantine of returning travellers, and strict isolation of proven cases as well as their first- pe er re v and second-generation contacts contributed to the rapid containment of the virus.2 As of 1st December 2020, 1,351 microbiologically confirmed cases of coronavirus disease of 2019 (COVID-19) had been reported, 51% of whom were returned travellers in quarantine.3 By this date there had been 35 deaths recorded as being due to COVID-19.1 However, it is possible that the number of reported cases may be an under-estimate the true incidence of disease This is because some people with the infection may not have been tested as they did not have symptoms, did not seek care, or were not able to access a virus-detection test Serological tests measure the antibody response to the virus, with a response evident from 1014 days after the onset of infection.4,5 Surveys in potentially exposed populations can be used ot to evaluate the true cumulative incidence of infection with SARS-CoV-2 and, by comparison tn with the reported incidence rate, to estimate the case detection rate.6 The prevalence of SARS-CoV-2 antibodies varies substantially between settings,5,7 reflecting rin the substantial variation in countries’ experience of the pandemic Countries implementing successful public health measures to reduce transmission – including physical distancing, ep effective quarantining of high-risk individuals and strict border controls – have reported a low prevalence of SARS-CoV-2 antibodies (seroprevalence) in the population For example, Pr sero-prevalence rates of less than 1% in the general population were reported in Greece, Malaysia, and in Sydney in mid-2020.8–10 In these settings, the number of confirmed cases may be similar to the number of infections In contrast, in high transmission settings, This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed including northern Europe and North America, the seroprevalence of infection in sampled populations has been reported to be as high as 12·5%.11–13 In Switzerland, due to low levels of confirmatory testing, for every confirmed SARS-CoV-2 case in the community, antibody testing revealed that a further 11·6 cases of SARS-CoV-2 infection had been undiagnosed.12 Health care workers (HCW) exposed to patients with COVID-19 are often reported to be at pe er re v the highest risk of infection, with antibody sero-prevalence reported between 6·4-24·4%.14–16 Vietnam shares a 1,300km northern border with China The first case of COVID-19 was diagnosed in Vietnam on the 23rd January 2020, in a returned traveller from Wuhan, China Within eight weeks, Vietnam had closed its national borders, introduced quarantine procedures, closed all schools and businesses, implemented physical distancing policies, and utilised comprehensive public health messaging to the population.17 All suspected and confirmed cases were required to enter mandatory quarantine at public facilities following ot risk assessment The presence of undetected transmission in Vietnam is unknown This study aimed to tn measure the prevalence of serological response to SARS-CoV-2 in communities where cases of COVID-19 were reported and among household contacts and healthcare workers exposed rin to patients known to have COVID-19 ep Methods Study design and setting Pr A cross-sectional study was performed in three provinces of Vietnam in which community transmission of SARS-CoV-2 had been detected Vietnam is a middle-income country in This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Southeast Asia with a population of 96 million Within each of its 63 provinces, healthcare is delivered by the provincial government’s Department of Health with support from the national Ministry of Health Each province is further sub-divided into districts, communes, and sub-communes Sub-communes usually have a population of between 500 and 2000 people pe er re v The first outbreak of COVID-19 occurred in northern Vietnam in January 2020 Approximately 70% of confirmed cases had acquired the virus overseas.17 Following 99 days with no detected community transmission of COVID-19, on 25 July 2020, Vietnam reported a new case of COVID-19 in a patient presenting with an acute respiratory illness to Da Nang Provincial Hospital This outbreak in central Vietnam quickly spread into the local community and 13 other provinces Despite an increase in community transmission, the outbreak was effectively controlled within a 40-day period, with a co-ordinated public health ot response Supplement shows the number of cases detected in affected provinces over time Site selection tn Sub-communes were eligible for inclusion in this study if they had at least two cases of COVID-19 confirmed based upon real time reverse transcriptase polymerase chain reaction rin (rRT-PCR) testing of nasal/ throat swabs Sites were selected to reflect both urban and rural settings and to include sub-communes with the highest cases numbers (Supplement 2) ep Finally, four sub-communes were selected These were in northern Vietnam: (i) Hoi subcommune in Ha Loi commune, Me Linh district, Hanoi Capital (where five cases of known COVID-19 were diagnosed in April 2020); and central Vietnam: (i) Giao Ai sub-commune in Pr Dien Hong commune, Dien Ban, Quang Nam Province (three cases of known COVID-19 in August 2020); (ii) Luu Minh sub-commune in Ha Lam Town, Quang Nam (seven cases of 10 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed References John Hopkins University COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University [Internet] John Hopkin’s University 2020 [updated 2020 Dec 31, cited 2020 Dec 31] Available from: https://coronavirus.jhu.edu/map.html Thanh HN, Van TN, Thu HNT, Van BN, Thanh BD, Thu HPT, et al Outbreak pe er re v investigation for COVID-19 in northern Vietnam Lancet Infect Dis 2020 Mar;20:535–6 Vietnam Ministry of Health Bo Y Te: Trang tin ve dich benh viem duong ho hap cap COVID-19 [Internet] Vietnam Ministry of Health 2020 [cited 2020 Dec 1] Available from: https://ncov.moh.gov.vn/ Van Elslande J, Houben E, Depypere M, Brackenier A, Desmet S, André E, et al Diagnostic performance of seven rapid IgG/IgM antibody tests and the Euroimmun IgA/IgG ELISA in COVID-19 patients Clin Microbiol Infect 2020 Aug;26(8):1082–7 Hanson K, Caliendo A, Arias C, Englund J, Hayden M, Lee M Infectious Diseases ot Society of America guidelines on the diagnosis of COVID-19: Serological testing [Internet] tn Infectious Diseases Society; 2020 [updated 2020 Aug 18, cited 2020 Dec 1] Available from: https://www.idsociety.org/practice-guideline/covid-19-guideline-serology/ Pouwels KB, House T, Robotham J V, Birrell P, Gelman AB, Bowers N, et al rin Community prevalence of SARS-CoV-2 in England: Results from the ONS Coronavirus ep Infection Survey Pilot Lancet 2020 Dec;6(1):e30-38 Ng OT, Marimuthu K, Koh V, Pang J, Linn KZ, Sun J, et al SARS-CoV-2 seroprevalence and transmission risk factors among high-risk close contacts: a retrospective Pr cohort study Lancet Infect Dis 2020 Nov; DOI:https://doi.org/10.1016/S14733099(20)30833-1 21 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Bogogiannidou Z, Vontas A, Dadouli K, Kyritsi MA, Soteriades S, Nikoulis DJ, et al iew ed Repeated leftover serosurvey of SARS-CoV-2 IgG antibodies, Greece, March and April 2020 Euro Surveill 2020 Aug;25(31):pii 2001369 Sam I-C, Chong YM, Tan CW, Chan YF Low postpandemic wave SARS-CoV-2 seroprevalence in Kuala Lumpur and Selangor, Malaysia J Med Virol 2021 Feb; 93(2):6478 Gidding H, Machalek D, Hendry A, Quinn H, Vette K, Beard F, et al Seroprevalence pe er re v 10 of SARS-CoV-2-specific antibodies in Sydney, Australia following the first epidemic wave in 2020 Med J Aust 2020; https://www.mja.com.au/system/files/2020- 11/Gidding%20mja20.01971%20-%2011%20November%202020_0.pdf 11 Rosenberg ES, Tesoriero JM, Rosenthal EM, Chung R, Barranco MA, Styer LM, et al Cumulative incidence and diagnosis of SARS-CoV-2 infection in New York Ann Epidemiol 2020 Aug;48:23-29.e4 12 Stringhini S, Wisniak A, Piumatti G, Azman AS, Lauer SA, Baysson H, et al ot Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoVPOP): a population-based study Lancet 2020 Aug;396(10247):313–9 Pollán M, Pérez-Gómez B, Pastor-Barriuso R, Oteo J, Hernán MA, Pérez-Olmeda M, tn 13 et al Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based 14 rin seroepidemiological study Lancet 2020 Aug;396(10250):535–44 Galanis P, Vraka I, Fragkou D, Bilali A, Kaitelidou D Seroprevalence of SARS- ep CoV-2 antibodies and associated factors in health care workers: a systematic review and meta-analysis J Hosp Infect 2021 Feb;108:120-134 15 Moncunill G, Mayor A, Santano R, Jiménez A, Vidal M, Tortajada M, et al SARS- Pr CoV-2 seroprevalence and antibody kinetics among health care workers in a Spanish hospital after three months of follow-up J Infect Dis 2021 Jan;223(1):62-71 22 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Shields A, Faustini SE, Perez-Toledo M, Jossi S, Aldera E, Allen JD, et al SARS- iew ed 16 CoV-2 seroprevalence and asymptomatic viral carriage in healthcare workers: a crosssectional study Thorax 2020 Dec;75(12):1089–94 17 Thai PQ, Rabaa MA, Duong HL, Dang QT, Tran DQ, Quach H-L, et al The first 100 days of SARS-CoV-2 control in Vietnam Clin Infect Dis 2020 Aug; ciaa1130 doi: 10.1093/cid/ciaa1130 The National SARS-CoV-2 Serology Assay Evaluation Group Performance pe er re v 18 characteristics of five immunoassays for SARS-CoV-2: a head-to-head benchmark comparison Lancet Infect Dis 2020 Dec;20(12):1390–400 19 Vietnam Ministry of Health Temporary guideline for monitoring and prevention of COVID-19: Decision 3468/QD-BYT dated 7/8/2020 [Internet] 2020 [cited 2020 Dec 1] Available from: https://thuvienphapluat.vn/van-ban/The-thao-Y-te/Quyet-dinh-3468-QDBYT-2020-Huong-dan-tam-thoi-giam-sat-va-phong-chong-COVID-19-449407.aspx 20 Lewis N, Chu V, Ye D, Conners E, Gharpure R, Laws R, et al Household ot transmission of SARS-CoV-2 in the United States Clin Infect Dis 2020 Aug 16; ciaa1166 doi: 10.1093/cid/ciaa1166 Luo L, Liu D, Liao X, Wu X, Jing Q, Zheng J, et al Contact settings and risk for tn 21 transmission in 3410 close contacts of patients with COVID-19 in Guangzhou, China : A 22 rin prospective cohort study Ann Intern Med 2020 Dec;173(11):879–87 Vos ERA, den Hartog G, Schepp RM, Kaaijk P, van Vliet J, Helm K, et al ep Nationwide seroprevalence of SARS-CoV-2 and identification of risk factors in the general population of the Netherlands during the first epidemic wave J Epidemiol Community Pr Health 2020 Nov; doi: 10.1136/jech-2020-215678 23 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Chau NVV, Toan LM, Man DNH, Thao HP, Lan NPH, Ty DTB, et al Absence of iew ed 23 SARS-CoV-2 antibodies in health care workers of a tertiary referral hospital for COVID-19 in southern Vietnam J Infect 2021 Jan; 82(1):e36-37 24 Rosser JI, Röltgen K, Dymock M, Shepard J, Martin A, Hogan CA, et al SARS-CoV- Seroprevalence in healthcare personnel in Northern California early in the COVID-19 pandemic Infect Control Hosp Epidemiol 2020 Dec;1–7 Eyre DW, Lumley SF, O’Donnell D, Campbell M, Sims E, Lawson E, et al pe er re v 25 Differential occupational risks to healthcare workers from SARS-CoV-2 observed during a prospective observational study Elife 2020 Aug;9:e60675 26 Lai C-C, Wang J-H, Hsueh P-R Population-based seroprevalence surveys of anti- SARS-CoV-2 antibody: An up-to-date review Int J Infect Dis 2020 Dec;101:314–22 27 Stubblefield WB, Talbot HK, Feldstein L, Tenforde MW, Rasheed MAU, Mills L, et al Seroprevalence of SARS-CoV-2 among frontline healthcare personnel during the first month of caring for COVID-19 patients - Nashville, Tennessee Clin Infect Dis 2020 28 ot Jul;ciaa936 Chen Y, Tong X, Wang J, Huang W, Yin S, Huang R, et al High SARS-CoV-2 tn antibody prevalence among healthcare workers exposed to COVID-19 patients J Infect 2020 Sep;81(3):420–6 Long Q-X, Tang X-J, Shi Q-L, Li Q, Deng H-J, Yuan J, et al Clinical and rin 29 immunological assessment of asymptomatic SARS-CoV-2 infections Nat Med Pr ep 2020;26(8):1200–4 24 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 908 622 68·5 40 (19-54) 602 546 90·7 40 (23-58) to 13 Sep 13 to 23 Nov to 24 Nov 21 to 23 Nov to 23 Apr 25 to 31 Jul 24 Jul to Aug 19 to 20 weeks 16 to 17 weeks 2…4 Jul to Aug 16 to 17 weeks 1624 (53·3) 309 (53·7) 336 (54·0) 298 (54·6) 681 (52·1) 27 (0·9) (1·4) (0·6) (0·9) 10 (0·8) 53 (1·7) 2969 (97·4) 26 (4·5) 541 (94·1) 10 (1·6) 608 (97·7) 12 (2·2) 529 (96·9) (0·4) 1291 (98·9) 812 (26·6) 547 (17·9) 438 (14·4) 304 (10·0) 201 (6·6) 108 (3·5) 53 (1·7) 50 (1·6) 158 (27·5) 189 (32·9) 71 (12·3) 43 (7·5) (1·6) 14 (2·4) (0·5) (0·5) 153 (24·6) 69 (11·1) 126 (20·3) 48 (7·7) 72 (11·6) 41 (6·6) 10 (1·6) (1·1) 126 (23·1) 175 (32·1) 60 (11·0) 70 (12·8) 17 (3·1) 25 (4·6) (1·6) (1·3) 375 (28·7) 114 (8·7) 181 (13·9) 143 (10·9) 103 (7·9) 28 (2·1) 31 (2·4) 33 (2·5) (0·2) (0·0) 11 (1·8) (0·0) (0·2) (0·2) (0·2) (0·1) (0·0) (0·0) (0·2) (0·0) (0·0) (0·0) 518 (17·0) (0·0) 84 (14·6) (0·0) 84 (13·5) (0·0) 55 (10·1) (0·0) 295 (22·6) 429 (14·1) 212 (7·0) 85 (2·8) 61 (2·0) 43 (1·4) 89 (15·5) 41 (7·1) 17 (3·0) 18 (3·1) (1·2) 91 (14·6) 50 (8·0) 13 (2·1) (1·3) (1·3) 92 (16·8) 43 (7·9) 18 (3·3) 16 (2·9) 14 (2·6) 157 (12·0) 78 (6·0) 37 (2·8) 19 (1·5) 14 (1·1) 30 (1·0) (0·7) (1·1) (0·7) 15 (1·1) (0·2) (0·9) (0·0) (0·2) (0·1) (0·0) (0·0) (0·0) (0·0) (0·1) 3747 3049 81·4 37 (19-53) 15 (0·5) (0·1) ep Pr Luu Minh Commune Giao Ai Commune pe er re v 719 575 80·0 36 (18-55) Le Son Nam Commune 1518 1306 86·0 33 (17-49) rin N Number enrolled Participation rate (%) Age, years (median, interquartile range) Period of serological testing Period of local outbreak Time from end of outbreak to testing Female gender, n (%) Category of exposure Household contacts, n (%) Close contacts (%) Community members (%) Occupation (%) Student* Farmer Self-employed Factory worker Office worker Retired Unemployed Service workers Health care worker Tourist Overseas students, returning home People returning home Other Comorbidities (%) Smoker Hypertension Heart disease Diabetes Renal disease Pulmonary disease Immunological disease Travel history since January 2020 (%) Outside Vietnam Hoi Commune ot Total tn Characteristics iew ed Table 1: Demographic profile and characteristics of all sub-communes 15 to 16 weeks 25 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 33 (5·7) (1·0) (1·6) (1·2) (0·3) (1·6) (0·0) (1·0) (1·0) (1·0) (0·2) (0·5) (0·2) (0·0) (0·0) (1·2) 43 (6·9) (1·0) 15 (2·4) 13 (2·1) 10 (1·6) (1·3) (0·5) (0·8) (0·3) (0·2) (0·6) (0·0) (0·2) (0·0) (0·0) (0·3) 64 (11·7) 18 (3·3) 10 (1·8) 10 (1·8) 22 (4·0) (0·7) 16 (2·9) (0·9) (0·7) (0·4) (0·5) (0·4) (0·2) (0·0) (0·0) (0·2) 22 (1.7) (0·5) (0·2) (0·5) (0·2) (0·2) (0·2) (0·1) (0·1) (0·2) (0·1) (0·0) (0·0) (0·1) (0·0) (0·2) 58 (35·8) 44 (27·2) 10 (30·2) (21·2) 20 (46·5) 10 (23·3) 22 (34·4) 22 (34·4) (27·3) (22·7) 25 (15·4) 23 (14·2) 15 (9·3) (6·1) 10 (30·3) (3·0) 11 (25·6) (9·3) (9·3) 11 (17·2) (9·4) (6·3) (4·5) (13·6) (27·3) (1·9) (1·9) (1·2) 23 (14·2) (0·0) (3·0) (6·1) (0·0) (21·2) (0·0) (2·3) (0·0) (2·3) (11·6) (0·0) (1·6) (1·6) (0·0) (9·4) (0·0) (0·0) (0·0) (4·5) (22·7) (0·0) Pr ep tn 162 (5·3) 36 (1·2) 37 (1·2) 36 (1·2) 36 (1·2) 24 (0·8) 22 (0·7) 17 (0·6) 13 (0·4) 12 (0·4) (0·3) (0·2) (0·1) (0·0) (0·0) 13 (0·4) rin Symptoms since January 2020 (%) Total Fatigue Nasal discharge Sore throat Headache Cough Myalgia Sputum Breathlessness Diarrhoea Fever Conjunctivitis Anosmia Chills Haemoptysis Other Actions taken by those who were symptomatic Take pharmacy medications Wait Take medications at home Visit clinic Self-isolate Already in hospital Visit doctor Get COVID test Other No action Reported frequency of actions taken by community (%) Hand washing pe er re v Central Vietnam* - Plane - Bus - Train - Private vehicle - Other Other local areas - Plane - Bus - Train - Private vehicle - Other Hoi Luu Minh Giao Ai Le Son Nam Commune Commune Commune Commune 180 (5·9) (0·0) 46 (7·4) 92 (16·8) 42 (3·2) (0·0) (0·2) (0·0) (0·3) (0·4) (0·3) (0·0) (0·0) (0·0) 44 (7·1) 92 (16·8) 39 (3·0) (0·3) (0·2) (0·1) 591 (19·4) 104 (18·1) 151 (24·2) 174 (31·9) 162 (12·4) 33 (5·7) 15 (2·4) (0·7) 47 (3·6) 26 (6·3) 22 (3·5) 13 (2·4) 45 (3·4) (0·2) (0·0) (0·0) (0·5) 58 (10·1) 107 (17·2) 147 (26·9) 87 (6·7) (0·3) (0·8) (1·3) (0·2) iew ed Total ot Characteristics 26 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Hoi Luu Minh Giao Ai Le Son Nam Commune Commune Commune Commune 2379 (78·0) 507 (88·2) 470 (75·6) 388 (71·1) 1014 (77·6) 576 (18·9) 62 (10·8) 108 (17·4) 116 (21·2) 290 (22·2) 100 (3·3) (1·0) 45 (7·2) 45 (8·2) (0·3) - Very often - Sometimes - Not at all Wearing a mask - Very often - Sometimes - Not at all Attending social gatherings - Very often - Sometimes - Not at all iew ed Total 2627 (86·2) 373 (12·2) 58 (1·7) 523 (91·0) 47 (8·2) (0·9) 523 (84·1) 78 (12·5) 22 (3·5) 442 (81·0) 85 (15·6) 25 (4·6) 1139 (87·2) 163 (12·5) (0·5) 526 (17·3) 650 (21·3) 1886 (61·9) 74 (12·9) 136 (23·7) 365 (63·5) 107 (17·2) 127 (20·4) 387 (62·2) 302 (55·3) 172 (31·5) 75 (13·7) 43 (3·3) 215 (16·5) 1049 (80·3) Pr ep rin tn ot *includes school and university students pe er re v Characteristics 27 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Table 2: Characteristics of exposure to COVID-19 cases by household and close contacts Luu Minh Commune Cluster Giao Ai Le Son Nam Commune Commune 10 4·3 2·6 2·5 27 2·3 1·0 1·1 13·5 5·3 3·8 4·0 53 1·3 26 1·1 10 1·7 1·3 3·7 1·5 2·2 5·2 7·3 5·8 5·5 12 1·5 1·2 2·3 1·6 0·9 1·2 pe er re v Household exposure Average number of COVID-19 contacts Average number of encounters* Average number of hours per exposure Close contact Average number of contacts Average number of encounters* Average number of hours per exposure Hoi Commune iew ed Total Pr ep rin tn ot *A single encounter is considered significant if >2 hours in duration or within 2meters distance for 15 minutes 28 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 n 148 148 69 (46%) 32 (23-62) 24 to 30 Nov 30 Jan to 26 Nov 9·4 (5·4 – 14·8) 100 (67·6) 59 (39·9%) 89 (60·1%) Pr ep rin tn ot pe er re v Characteristic Total number of participants Number who had serology performed Number who had PCR performed* Age years (median, IQR) Timing of serology Timing of exposure Number of weeks between exposure and serology (median, IQR) Female, n (%) Healthcare facility Danang Lung Hospital Hoa Vang District Hospital Exposure history Number of days between first exposure and serology (median, IQR) Number of days between last exposure and serology (median, IQR) Number of days of contact (median, IQR) Number of hours of contact per day (median, IQR) Occupation (%) Nurse Doctor Allied Health Healthcare assistant Laboratory technician Number of individuals with any infective symptoms since January 1, 2020 (%) Headache Fever Sore throat Rhinorrhoea Dry cough Fatigue Chills Sputum Myalgia Breathlessness Haemoptysis Anosmia/dysgeusia Diarrhea Conjunctival symptoms Other Comorbidities among those with symptoms Hypertension Diabetes Pulmonary disease Renal disease Heart disease Immunological disease iew ed Table 3: Characteristics of health care workers participating in the study 117 (115 – 119) 44 (36-50) 40 (30-48·5) (2-8) 81 (54·4) 35 (23·5) 14 (9·4) 10 (6·7) (6·0) 12 (8·1) (6·0) (6·0) (5·4) (4·0) (4·0) (2·0) (2·0) (1·3) (0·7) (0·0) (0·0) (0·0) (0·0) (0·0) (4·7) (0·7) (2·0) (0·7) (0·7) (0·0) 29 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 IQR interquartile range, PCR nucleic acid testing Pr ep rin tn ot pe er re v iew ed *All health care workers had RT-PCR testing as part of standard workplace requirements between August and November 2020 For ther purposes of this study, RT-PCR was performed in symptomatic individuals only 30 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Overall Hoi Commune Luu Minh Commune 13 / 3034 (0·4%; / 570 (1·05%; / 616 (0·2%; 95%CI 0·3-0·7%) 95%CI 0·5-2·3%) 95%CI 0·0-0·9%) / 27 (18·5%; / (50·0%; 95%CI / (0%) 95%CI 8·2-36·7%) 21·5-78·5%) / 53 (1·9%; 95%CI / 26 (3·9%; 95%CI 0·3-9·9%) 0·7-18·9%) / 2954 (0·2%; / 536 (0·2%; / 602 (0·2%, 95%CI 0·1-0·5%) 95%CI 0·0-1·1%) 95%CI 0·0-0·9%) 95%CI 0·1-0·9%) 31·7; 95%CI 10·9- 78·9; 95%CI 9·5- 13·4; 95%CI 0·6- 17·2; 95%CI 2·1- 92·0 656·0 316·2 138·3 Overall Household contacts Close contact Community Relative risk of infection for contacts versus community members Giao Ai Commune Le Son Nam Commune / 545 (0%) / 1303 (0·5%; 95%CI 0·2-1·0%) / (0%) / 10 (0%) / 12 (0%) / 528 (0%) / (0%) / 1288 (0·4%; Pr ep rin tn ot CI Confidence interval /10 (10%; 95%CI 1·8-40·4%) pe er re v Population iew ed Table 4: Prevalence of seropositivity within high-risk populations, grouped by cluster 31 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Number (%) 35 (22-49) (38·5%) (7·7%) (53·8%) (30·8) (23·1) (15·4) (15·4) (7·7) tn ot pe er re v Characteristic Age, years (median, IQR) Household contacts Close contacts Community members Occupation (%) Student Self-employed Factory worker Farmer Retired Comorbidities (%) Smoker Heart disease Hypertension Diabetes Renal Disease Pulmonary disease Immunological disease Reported frequency of actions taken (%) Hand washing - Very often - Sometimes - Not at all Mask - Very often - Sometimes - Not at all Attending social gatherings - Very often - Sometimes - Not at all iew ed Table 5: Characteristics of individuals positive for SARS-CoV-2 (7·7) (7·7) (7·7) (0·0) (0·0) (0·0) (0·0) 11 (84·6) (15·4) (0·0) 12 (92·3) (0·0) (7·7) (7·7) (7·7) 11 (84.6) Pr ep rin IQR interquartile range 32 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 12 10 ot tn rin 3/09/2020 3/10/2020 15/03/2020 6/08/2020 28/07/2020 30/07/2020 31/07/2020 8/01/2020 8/02/2020 8/03/2020 8/04/2020 8/05/2020 8/06/2020 8/07/2020 8/08/2020 8/09/2020 8/10/2020 8/11/2020 13/08/2020 14/08/2020 15/08/2020 17/08/2020 18/08/2020 19/08/2020 20/08/2020 10/02/2020 25/10/2020 11/10/2020 ep Pr Imported cases Figure 1b: Daily new cases of COVID-19 in Da Nang between March and November 2020 50 40 30 20 10 Imported cases Imported cases 25/11/2020 10 11/11/2020 15 31/10/2020 20 28/08/2020 25 25/08/2020 23/08/2020 21/08/2020 19/08/2020 17/08/2020 15/08/2020 13/08/2020 8/11/2020 8/09/2020 Figure 1a: Daily new cases of COVID-19 in Hanoi between May and November 2020 iew ed 3/05/2020 3/08/2020 13/03/2020 15/03/2020 17/03/2020 19/03/2020 21/03/2020 23/03/2020 25/03/2020 27/03/2020 29/03/2020 31/03/2020 4/02/2020 4/06/2020 4/08/2020 4/10/2020 4/12/2020 14/04/2020 18/05/2020 29/07/2020 31/07/2020 8/06/2020 8/08/2020 8/12/2020 17/08/2020 28/08/2020 9/08/2020 28/09/2020 11/04/2020 23/11/2020 pe er re v 8/07/2020 8/05/2020 8/03/2020 8/01/2020 30/07/2020 28/07/2020 26/07/2020 25/03/2020 18/03/2020 3/08/2020 Supplement 1: COVID-19 case numbers over time in selected provinces in Vietnam Local cases Local cases Figure 1c: Daily new cases of COVID-19 in Quang Nam between September and October 2020 Local cases 33 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 Supplement 2: Confirmed COVID-19 case numbers in communes in Da Nang and Quang Nam iew ed Table 1a: Confirmed COVID-19 case numbers by commune in Da Nang No of clusters which had cases cases 2 rin cases cases 1 1 pe er re v cases cases 1 1 1 1 1 ot 1 1 1 1 1 1 Pr ep cases tn Commune Setting Hòa Xuân Urban Khuê Trung Urban Hòa An Urban Hịa Phát Urban Bình Thuận Urban Hải Châu Urban Hịa Cường Urban Nam Hịa Thuận Urban Đơng Nam Dương Urban Phước Ninh Urban Hòa Thuận Urban Tây Hòa Phong Rural Hòa Phước Rural Hòa Tiến* Rural Hòa Khánh Urban Bắc Hòa Minh Urban An Hải Bắc Urban An Hải Đông Urban Nại Hiên Urban Đông Phước Mỹ Urban Thọ Quang Urban An Khê Urban Chính Gián Urban Hịa Khê Urban Tam Thuận Urban Tân Chính Urban Thạch Khê Urban Đông Thạch Khê Urban Tây Mỹ An Urban * selected commune 34 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 iew ed Table 1b: Confirmed COVID-19 case numbers by commune in Quang Nam No of clusters which had cases cases cases cases cases cases cases 1 1 pe er re v 1 Pr ep rin tn ot Commune Setting Minh An Urban Cẩm An Urban Hà Lam* Urban Duy Trung Rural Điện Hồng* Rural Điện Thọ Rural Điện Trung Rural * selected commune 35 This preprint research paper has not been peer reviewed Electronic copy available at: https://ssrn.com/abstract=3781699 ... community members The determination of sero- prevalence in high- risk populations in Vietnam can provide an insight into understanding if the strict physical distancing and quarantine policies have... writing – review and editing Truong Tan Nam: investigation, project administration, writing – review and editing Vo Trung Hoang: investigation, project administration, writing – review and editing... https://ssrn.com/abstract=3781699 iew ed Le Van Duyet: investigation, project administration, writing – review and editing Dang Thi Thuy: investigation, project administration, writing – review and editing Van Dinh Trang: investigation,