key: cord-0853762-kwb2v7z8 authors: Hasan, Tasnim; Thach, Pham Ngoc; Anh, Nguyen Thu; Hien, Le Thi Thu; An, Nguyen Thi Mai; Thuy, Dang Thi; Van Duyet, Le; Dung, Nguyen Thi; Diep, Tran Thi; Van Huynh, Hoang; Toelle, Brett; Marks, Guy B.; Fox, Greg J. title: The prevalence of SARS-CoV-2 antibodies in quarantine workers and high-risk communities in Vietnam date: 2021-12-11 journal: IJID Regions DOI: 10.1016/j.ijregi.2021.12.001 sha: 51b058dd3aae99e4cfd7ca567c4b8b38cad75619 doc_id: 853762 cord_uid: kwb2v7z8 Objective We determined the sero-prevalence of severe acute respiratory syndrome – coronavirus – 2 (SARS-CoV-2) antibodies in high-risk communities and quarantine workers in Vietnam. Methods We measured the prevalence of SARS-CoV-2 antibodies in household contacts, close contacts, community members, and migrant workers from two sub-communes in which COVID-19 outbreaks occurred in early 2021: Bac Ma 1 and Tien. We evaluated the prevalence of SARS-CoV-2 antibodies among quarantine workers at two facilities responsible for quarantine of contacts of COVID-19 cases. Results Among 2,069 participants, six individuals (0.3%) had detectable SARS-CoV-2 antibodies despite no history of COVID-19. This included one Vietnamese migrant worker, two community members, two household contacts and one close contact of known COVID-19 cases. Among 50 workers at two COVID-19 quarantine facilities, including 15 health care workers (HCW), one of the HCW tested positive for SARS-CoV-2 antibodies (1/50, 2.0%) despite no known disease. Conclusion The prevalence of SARS-CoV-2 antibodies was low in Vietnamese ‘hotspots’, suggesting limited community transmission. Vietnam, a populous nation in Southeast Asia, had detected a small number of cases of COVID-19 compared to many other global settings prior to April 2021. Community transmission was prevented using strict public health strategies including mandatory quarantine for returned travellers, isolation of all community members in domestic epidemic areas and isolation of contacts of confirmed COVID-19 cases (Nguyen et al 2020) . Quarantine for all close contacts of people with confirmed COVID-19 was delivered by staff who worked and lived in the facilities, to minimise community exposure. These staff were provided with accommodation and personal protective equipment (PPE). Furthermore, staff were required to undergo mandatory two-week quarantine and negative polymerase chain reaction (PCR) testing for severe acute respiratory syndromecoronavirus -2 (SARS-CoV-2) before returning to the community. These interventions were associated with a low case notification rate. However, notifications may underestimate the true community incidence of COVID-19. This seroprevalence study aimed to measure the prevalence of unrecognised infection in the general community and among quarantine workers at high-risk of exposure to SARS-CoV-2. A cross-sectional survey was undertaken to measure the prevalence of SARS-CoV-2 antibodies in two northern provinces. Vietnam is a middle-income country with a population of 96 million. Each of its 63 provinces can be subdivided into districts, communes, and subcommunes. Sub-communes usually have a population of between 500 and 2000 people. Between January 1 and February 28, 2021, Bac Mac 1 sub-commune in Quang Ninh province and Tien sub-commune in Hai Duong province reported 7 and 18 cases of COVID-19, respectively. These two sub-communes, both in North Vietnam, had the highest number of cases during Vietnam's third epidemic wave. We invited all household and close contacts of COVID-19 cases and all community members, residing in the two selected sub-communes, to participate in the study. A list of community members for each sub-commune were obtained from local authorities. An invitation letter and information sheet were sent to each household with details of the study. Community members were invited to a study location. For those who did not attend, the study team visited the house to further extend an invitation to participate voluntarily in the study. Individuals in Bac Mac 1 sub-commune were interviewed over a one-week period 12 weeks after the local outbreak and individuals from Tien sub-commune were interviewed 9 weeks after the local outbreak (Table 1 ). Secondly, we tested clinical and non-clinical quarantine workers at two isolation facilities in Quang Ninh province, which housed contacts of COVID-19 cases and had the highest number of COVID-19 diagnosed among contacts. Only two facilities were included due to time and funding limitations. Participants completed a baseline demographic survey and gave blood for SARS-CoV-2 antibody testing using the validated cobas platform (Roche Diagnostics), with an estimated sensitivity and specificity of 96.8% and 99.8%, respectively, for samples taken at least 14 days after symptom onset (The National SARS-CoV-2 Serology Assay Evaluation Group, 2020). The current study was completed prior to the delivery of vaccination against SARS- Ethical approval was obtained from the University of Sydney (HREC 2020/415) and the National Hospital for Tropical Diseases (No. 10/HDDD-NDTU, No. 18/HDDD-NDTU, No. 02/HDDD-NDTU). Data and consent records were electronically stored using a REDCap Database. Participants received a small reimbursement to compensate for their time. A total of 897 unvaccinated individuals in Bac Ma 1 sub-commune and 1172 individuals in Tien sub-commune (including 212 Vietnamese migrant workers) were enrolled in this study ( Table 1 ). The participation rate was approximately 80% and 31% for community residents and migrant workers respectively. In the community, six individuals (6/2069, 0.3%), had detectable SARS-CoV-2 antibodies including one migrant worker (1/212, 0.5%), two community members (2/1796, 0.1%), two household contacts (2/29, 6.9%) and one close contact (1/32, 3.1%) of known COVID-19 cases. The age of individuals with positive serology ranged from 9 to 67 years, three were female (50.0%). In the quarantine facilities, 50 quarantine workers were screened (participation rate 50/53, 94.3%). Of these, one of 15 health care workers (HCW) (1/50, 2.0%) had detectable SARS-CoV-2 antibodies ( Table 2 ). All seven cases were diagnosed incidentally during the study period and did not report symptoms during the outbreak period or while working at quarantine facilities. None of the positive cases required treatment, admission or support for COVID-19 during the study period. This population-wide survey in COVID-19 hotspots during Vietnam's third wave demonstrates a low prevalence of SARS-CoV-2 antibodies among members of the general community and quarantine workers. This is among the first studies of seroprevalence of SARS-CoV-2 in workers at dedicated quarantine facilities. The finding of one HCW with detectable SARS-CoV-2 antibodies is comparable to studies in In conclusion, the prevalence of SARS-CoV-2 antibodies in quarantine workers and in communities was low during a community outbreak of COVID-19. Given the low rates of prevalent immunity to the virus, COVID-19 vaccination will be critical to long-term community protection community amidst future outbreaks in Vietnam. This project was supported by a grant funded by the Australian Department of Foreign Affairs and Trade, awarded in conjunction with the Australian National Health and Medical Research Council (APP1153346). Ethical approval was obtained from the University of Sydney (HREC 2020/415) and the National Hospital for Tropical Diseases (No. 10/HDDD-NDTU, No. 18/HDDD-NDTU, No. Database. Participants received a small reimbursement to compensate for their time. We acknowledge the contributions to this study made by healthcare workers from National The data used for this research, including deidentified participant data and data dictionary, are available from the corresponding author on request. Absence of SARS-CoV-2 antibodies in health care workers of a tertiary referral hospital for COVID-19 in southern Vietnam Sero-Prevalence of SARS-CoV-2 Antibodies in High-Risk Populations in Vietnam High seroprevalence of SARS-CoV-2 in elderly care employees in Sweden SARS-CoV-2 and work-related transmission: results of a prospective cohort of airport workers Experience in responding to COVID-19 outbreaks from Vietnam. Lancet Reg Health West Pac The National SARS-CoV-2 Serology Assay Evaluation Group. Performance characteristics of five immunoassays for SARS-CoV-2: a head-to-head benchmark comparison The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.