{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,27]],"date-time":"2026-08-27T02:15:12Z","timestamp":1787796912113,"version":"build-2784847793"},"reference-count":38,"publisher":"BMJ","issue":"5","license":[{"start":{"date-parts":[[2026,5,15]],"date-time":"2026-05-15T00:00:00Z","timestamp":1778803200000},"content-version":"unspecified","delay-in-days":14,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"name":"Health and Medical Research Fund, Food and Health Bureau, Government of the Hong Kong Special Administrative Region","award":["COVID190119"],"award-info":[{"award-number":["COVID190119"]}]},{"name":"Research Grants Council of the Hong Kong Special Administrative Region, China","award":["T11-705\/21-N"],"award-info":[{"award-number":["T11-705\/21-N"]}]}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Open"],"accepted":{"date-parts":[[2026,4,21]]},"published-print":{"date-parts":[[2026,5]]},"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>In the first 2 years of the COVID-19 pandemic, Hong Kong adopted strict public health and social measures to stop community transmission of SARS-CoV-2. These include border screening and control, isolation of cases and quarantine of their contacts and universal masking. During this period, attack rates in Hong Kong were among the lowest globally.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Objectives<\/jats:title>\n                    <jats:p>To estimate the seroprevalence of COVID-19 among healthcare workers (HCWs) in Hong Kong in 2020 and 2021.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>We reviewed contact tracing data from the Hong Kong Department of Health to identify COVID-19 cases reported among HCWs. Between June 2020 and December 2021, we conducted a longitudinal cohort study to estimate the seroprevalence of COVID-19 among HCWs working in hospitals and clinics in Hong Kong during the first 2 years of the COVID-19 pandemic.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Overall seropositivity of COVID-19 by plaque reduction neutralisation test during the first (May\u2013October 2020) and second round (November 2020\u2013April 2021) of the study was 0% (95% CI 0.00% to 0.49%) and 0.52% (95% CI 0.14% to 1.33%). After COVID-19 vaccines were offered to HCWs in February 2021, seroprevalence by surrogate virus neutralisation assay among cohort participants who provided biannual blood samples rose to 68.7% (95% CI 65.9%, 71.3%) and 80.2% (95% CI 76.8%, 83.2%) in round 3 (May\u2013October 2021) and the first 2\u2009months of round 4 (November\u2013December 2021).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>Seroprevalence in Hong Kong HCWs in our study was low despite considerable exposure to confirmed COVID-19 cases in some study participants. However, the low rate of community transmission may have also contributed to the observed low seroprevalence among HCWs in our cohort.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjopen-2025-110192","type":"journal-article","created":{"date-parts":[[2026,5,16]],"date-time":"2026-05-16T07:55:31Z","timestamp":1778918131000},"page":"e110192","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":1,"title":["Seroprevalence of COVID-19 among healthcare workers in Hong Kong during the first 2 years of the COVID-19 pandemic (2020\u20132021): a longitudinal cohort study"],"prefix":"10.1136","volume":"16","author":[{"given":"Wey Wen","family":"Lim","sequence":"first","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Loretta","family":"Mak","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Faith","family":"Ho","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tiffany W Y","family":"Ng","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Emily Mun","family":"Yau","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ronald L W","family":"Ko","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dongxuan","family":"Chen","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jingyi","family":"Xiao","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wing Hong","family":"Seto","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Samuel M S","family":"Cheng","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ranawaka A P M","family":"Perera","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dennis K M","family":"Ip","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Malik","family":"Peiris","sequence":"additional","affiliation":[{"name":"Division of Public Health Laboratory Sciences, The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6297-7154","authenticated-orcid":false,"given":"Benjamin J","family":"Cowling","sequence":"additional","affiliation":[{"name":"The University of Hong Kong, Hong Kong, Hong Kong"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,5,15]]},"reference":[{"key":"2026051600551466000_16.5.e110192.1","doi-asserted-by":"publisher","DOI":"10.7326\/0003-4819-141-9-200411020-00006"},{"key":"2026051600551466000_16.5.e110192.2","unstructured":"Department of Health of the Government of the Hong Kong SAR . 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