香港醫護人員2019冠狀病毒病的血清陽性率：前瞻性追蹤隊列研究 Seroprevalence of COVID-19 in healthcare workers in Hong Kong:
a longitudinal cohort study (HCW study)

最新消息(2026-06)：本研究現已完成，感謝閣下過去六年參與本研究的跟進，我們衷心感謝閣下的支持！

簡介

2019冠狀病毒病疫情已對世界造成很大的影響。 世界各地的醫護人員因為在提供醫療服務時可能有機會接觸新型冠狀病毒比其他人群承受更大的影響。

我們在進行一項香港醫護人員中新型冠狀病毒抗體血清陽性率的縱向研究，以估算從2019冠狀病毒病剛開始在香港肆虐時至四年後(2020年5月至2024年2月)在港醫護人員中新型冠狀病毒抗體血清陽性率。 此研究的目的是讓我們更深入了解2019冠狀病毒病對醫護人員的影響及評估醫護人員感染新型冠狀病毒的危險因素。除此之外，由於新冠疫苗已可供接種，我們亦需要了解影響香港醫護人員對新冠疫苗和流感疫苗免疫反應的因素。

誰負責本研究及資金來源

這項研究由香港大學李嘉誠醫學院公共衛生學院高本恩教授領導，並獲食物及衛生局醫療衛生研究基金的COVID-19研究資助。

本研究已獲香港大學／醫院管理局港島西醫院聯網研究倫理委員會批准。

本人是否合資格參與此研究？

年滿18歲以上及在香港任職六個月以上的全職醫護人員，包括在醫院或診所裡的醫生、護士、支援及管理人員以及在救護車工作的輔助醫療人員等均可參與本研究。如果您不再任職於香港的醫院或診所或不再從事救護工作，將毋須繼續參與本研究。

您的參與純屬自願。 您可隨時電郵研究團隊：hcwsero@hku.hk 退出研究。

本人參與此研究以後將會有什麼安排？

  • 如果您符合本研究的參與資格及同意參與我們的研究，我們會在研究期間定期聯絡您以查詢您的健康狀況。
  • 我們的研究人員也會經您同意每半年向您採集血液樣本，用作進行新型冠狀病毒的免疫測試。為答謝您參與本研究所花耗的時間及對本研究的支持，在每次研究跟進期內提供血液樣本後，我們會給予您港幣50元超級市場禮券。
  • 我們也會在每個月通過電郵、電話或WhatsApp 短訊跟進您有否出現急性呼吸道感染。

本研究亦為計劃接種或已接種新冠肺炎疫苗/流感疫苗人士開設子研究

除了上述隨訪程序外，如果您將會接受由香港政府為醫護人員推出的新型冠肺炎疫苗接種計劃，我們將邀請您在接種任何一劑疫苗後21至35天進行額外的隨訪（除復必泰第一劑後的隨訪可安排於接種後的14至35天）。

另外，我們亦邀請計劃接種或已接種流感疫苗的醫護人員進行額外的隨訪。隨訪期的跟進時間為接種流感疫苗後的21至35天。

隨訪期間您將會接受研究人員的採訪，並會被抽取約10毫升血液樣本作為此研究子項目的用途。為答謝您額外花耗時間及對子研究項目的支持，在每次子研究的隨訪中提供接種疫苗後的血液樣本後，我們會給予您面額港幣100元超級市場禮券。

本人如何參與此研究？

  1. 請您回答以下幾個問題，並提供您的聯繫方式，讓我們評估您是否符合此研究的參與資格。
  2. 我們將通過您選擇的聯繫方式提供有關此研究的詳細資料，並在獲得您的同意後提供一個線上基本資料問卷的連結並邀請您完成此問卷。
  3. 我們以上提供的鏈接是一個只屬於您的鏈接，而您將來也會運用此鏈接來回答我門在這研究接下來的問卷。
  4. 我們的研究人員會在您完成第一份問卷後再聯絡您預約採集血液樣本的時間和地點。

資料保密

我們將會依照香港大學的私隱政策聲明將您的個人資料,包括您的聯繫方式、個人資料、或任何實驗結果絕對保密。

Update (2026-06): This study has now been completed. Thank you for your participation over the past 6 years! We truly appreciate your support!

Introduction

The coronavirus disease 2019 (COVID-19) pandemic has caused great public health impact worldwide. In many countries, health care workers are disproportionately affected as they can be exposed to the SARS-CoV-2 virus when providing services and care to patients who may have the disease.

We are conducting a research study to estimate the seroprevalence of antibodies to the SARS-CoV-2 virus among health care workers in Hong Kong for up to four years since the detection of the first COVID-19 cases in Hong Kong (May 2020 to February 2024). The purpose of this study is to help us better understand the impact of COVID-19 among health care workers and more importantly, the risk factors of infections among health care workers. Moreover, with COVID-19 vaccines are now available as well as influenza vaccines, it is also important for us to identify factors associated with immune responses to COVID-19 vaccines and influenza vaccines.

Who is conducting this study and how is it funded?

This study is led by Professor Benjamin Cowling from the School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong and funded by the Food and Health Bureau through the Health and Medical Research Emergency Fund for COVID-19 research.

This research has been approved by the Institutional Review Board of the University of Hong Kong / Hospital Authority Hong Kong West Cluster.

Am I eligible to participate in this study?

You will be eligible to participate in this study if you are above 18 years old, and have been working as a full time health care worker for at least 6 months in Hong Kong. This includes doctors, nursing staff, allied health professionals, supporting and management staff working in different departments of the hospital or clinics as well as paramedics and first aiders who provide ambulance services. You will be withdrawn from this study if you are no longer working in a hospital or clinic or as a paramedic in Hong Kong.

Your decision to participate in our study is voluntary, and you can withdraw your participation at any time by emailing the research team at hcwsero@hku.hk.

What will I expect if I participate?

  • If you are eligible and consent to take part in this study, we will contact you during the selected periods to collect information about your health.
  • Our healthcare personnel will collect blood specimens from you for a serological test to detect anti-SARS-CoV-2 virus antibodies twice a year. To appreciate your time spent and support for our study, you will receive $50 supermarket coupon for each blood draw visit.
  • We will contact you monthly via your preferred contact method (email, telephone calls, or WhatsApp messages) to ask you about any acute respiratory illness.

Sub-research project is available for participants who have received their COVID-19 vaccines and influenza vaccines

In addition to the above follow-up visits, if you receive COVID-19 vaccination which is offered by Hong Kong Government for health care workers, we would like to invite you for additional follow-up visits. The follow-up visits will be scheduled within 21 to 35 days after each dose of subsequent COVID-19 vaccination. (For those who receive BioNtech as their first dose, their first follow up visit will be scheduled within 14 to 35 days.)

Moreover, we would also like to invite you for another additional follow-up visit if you receive seasonal influenza vaccination. The follow-up visit will be scheduled within 21 to 35 days after injection.

During these visits, you will be interviewed and we will collect up to 10ml of blood for the purpose of this research sub-study. In addition, to thank you for your extra time and support for our sub-research project, you will receive supermarket coupon valued at HK$100 for each post-vaccination visit for blood draws.

How do I participate in this study?

  1. Please answer a few questions below and provide your contact information for us to assess your eligibility for the study.
  2. We will contact you by your preferred contact method to provide detailed information about the study, obtain your informed consent to participate in the study, and provide you with a unique link to answer an online questionnaire.
  3. You will use this unique link in the future to answer monthly follow-up questionnaires.
  4. After completing the first questionnaire, we will contact you to make an appointment to visit our study site for the collection of a blood sample.

Data confidentiality and privacy policy

We will keep your information, including your contact details, your personal information, or any laboratory testing results strictly confidential in accordance with the University of Hong Kong Privacy Policy Statement.

研究結果 Study findings

研究結果 Findings

研究結果 Findings

下載報告（PDF） Download report (PDF)

Seroprevalence of COVID-19 in healthcare workers in Hong Kong:
a longitudinal cohort study (HCW study)

The Hong Kong healthcare worker cohort (2020 - 2026)

The HCW study was established in 2020 as a prospective cohort study among healthcare workers in Hong Kong to estimate the seroprevalence of SARS-CoV-2 antibodies, evaluate vaccine immunogenicity and effectiveness, and assess the durability of SARS-CoV-2 protection induced by vaccination and infection.1,2 Supported by two grants from the Health and Medical Research Fund of the Health Bureau, we enrolled 1,752 participants and collected 16,875 blood samples over the course of the study. With your support, we have been able to map SARS-CoV-2 epidemiology in healthcare workers, measure the performance of mRNA and inactivated COVID-19 vaccines, and understand the durability of immunity against infections and re-infections across distinct phases of the pandemic.

COVID-19 epidemiology in Hong Kong

In 2020 and 2021, Hong Kong experienced several waves of SARS-CoV-2 infections, which were effectively contained through stringent public health interventions.3 Our analyses showed that fewer than 1% of participating healthcare workers had been infected by December 2021.1 Vaccines were available since early 2021, and most participants had received two doses by August 2021 and a third dose by May 2022 (see Figure 1, panel B below).

Figure 1. Panel A: Confirmed SARS-CoV-2 cases in Hong Kong. Panel B: Cases reported in the cohort and changes in vaccination uptake over time.
Figure 1. Panel A: Confirmed SARS-CoV-2 cases in Hong Kong. Panel B: Cases reported in the cohort and changes in vaccination uptake over time.

Tracking immunity through successive boosters

While our early work focused on the primary series,2 the multi-year timeline of this study allowed us to examine the antibody responses beyond the third dose. As visualized in Figure 2 panel A, participants in our cohort received up to 8 doses of COVID-19 vaccines over the six-year period to maintain protection. Our laboratory analysis of these samples, highlighted in Figure 2 panel B, provided insights into how immune systems responded to emerging variants:

  • Broadening Protection: We tracked neutralizing and binding antibodies not only against the ancestral strain but against highly mutated variants like BA.5 and JN.1.
  • The Booster Effect: Antibody levels reached very high peaks following the fourth, fifth, and sixth doses, indicating that the immune system remained highly responsive to repeated boosting.
  • Vaccine Performance: While CoronaVac stimulated lower antibody levels than BNT162b2, separate studies have shown that it still provided robust effectiveness against severe disease.

Antibody waning and hybrid immunity

Figure 2C maps out a critical reality of COVID-19 immunity: anti-SARS-CoV-2 antibodies wane over time. This decline is noticeable within 3 to 6 months, particularly following CoronaVac vaccination. However, the data also revealed that natural breakthrough infections provided a generally stronger and longer-lasting antibody response. By sharing these insights with health authorities, this cohort directly accelerated the government's November 2021 recommendation for third doses of COVID-19 vaccines to be administered, directly protecting the wider Hong Kong community.

Figure 2. Vaccination history (panel A), vaccine immunogenicity (panel B), and waning of anti-SARS-CoV-2 antibody after COVID-19 vaccination (panel C) among cohort participants.
Figure 2. Vaccination history (panel A), vaccine immunogenicity (panel B), and waning of anti-SARS-CoV-2 antibody after COVID-19 vaccination (panel C) among cohort participants.

What we are working on next

The blood samples you provided will continue to be an invaluable scientific resource. We are continuing to analyze samples and data collected in this study, with publications in preparation on the vaccine effectiveness of successive booster doses, the impact of hybrid immunity, reinfection rates after different vaccination or infection histories, and patterns in antibody dynamics after infections and re-infections.

Thank you for your participation in this study over the past 6 years! We truly appreciate your support!

References

  1. Lim WW, Mak L, Ho F, et al. Seroprevalence of COVID-19 among healthcare workers in Hong Kong during the first 2 years of the COVID-19 pandemic (2020–2021): a longitudinal cohort study. BMJ Open 2026; 16: e110192. [link]
  2. Lim WW, Mak L, Leung GM, Cowling BJ, Peiris M. Comparative immunogenicity of mRNA and inactivated vaccines against COVID-19. Lancet Microbe 2021; 2: e423. [link]
  3. Yang B, Lin Y, Xiong W, et al. Comparison of control and transmission of COVID-19 across epidemic waves in Hong Kong: an observational study. Lancet Reg Health West Pac 2024; 43: 100969. [link]
  4. Leung NHL, Cheng SMS, Cohen CA, et al. Comparative antibody and cell-mediated immune responses, reactogenicity, and efficacy of homologous and heterologous boosting with CoronaVac and BNT162b2 (Cobovax): an open-label, randomised trial. Lancet Microbe 2023; 4: e670–82. [link]
  5. McMenamin ME, Nealon J, Lin Y, et al. Vaccine effectiveness of one, two, and three doses of BNT162b2 and CoronaVac against COVID-19 in Hong Kong: a population-based observational study. Lancet Infect Dis 2022; 22: 1435–43. [link]

香港醫護人員2019冠狀病毒病的血清陽性率：前瞻性追蹤隊列研究

香港醫護人員前瞻性隊列研究(2020 - 2026)

「HCW研究」是一項由2020年起展開、以香港醫護人員為對象的前瞻性隊列研究。本研究旨在估算醫護人員中新型冠狀病毒（SARS-CoV-2）抗體的血清陽性率、評估新冠疫苗的免疫原性與有效性，並探討接種新冠疫苗及感染新冠病毒後所產生保護的持久性。1,2 在醫務衞生局轄下的「醫療衞生研究基金」所提供的兩項資助下，我們成功招募了1,752名參加者，並在研究期間收集了16,875份血液樣本。感謝閣下的卓越支持，使我們能夠了解香港醫護人員群組中，新冠病毒的流行病學特性、兩種新冠疫苗（信使核糖核酸疫苗與滅活疫苗）的免疫原性表現，以及於新冠病毒病大流行的不同階段下，針對初次感染與再次感染的免疫保護持久性。

香港「2019冠狀病毒病（COVID-19）」的流行病學

香港於2020至2021年間經歷了數波新冠疫情，然而透過嚴格的公共衞生干預措施，疫情均獲得有效控制。3 根據本研究分析顯示，截至2021年12月，僅有不到1%的參與研究醫護人員曾感染COVID-19。1自2021年初新冠疫苗開始供應後，大多數參加者已於2021年8月前完成接種兩劑新冠疫苗，並在2022年5月前接種了第三劑疫苗。（見圖 1B）。

圖1. 【A】香港確診新冠病毒病個案趨勢。【B】本研究中參加者通報的確診個案及疫苗接種率隨時間變化趨勢。
圖1. 【A】香港確診新冠病毒病個案趨勢。【B】本研究中參加者通報的確診個案及疫苗接種率隨時間變化趨勢。

追蹤後續加強劑的免疫表現

雖然我們早期的工作集中於基礎免疫劑次，2 但本研究跨越多年的時間線使我們能夠深入探討第三劑以後的抗體反應。正如圖 2A的疫苗接種史所示，本隊列的參加者在六年期間接種了多達 8 劑新冠疫苗以維持保護力。我們對這些樣本進行的實驗室分析（如圖 2B 所示）為免疫系統如何應對新興變異株提供了關鍵見解：

  • 開拓更廣泛的保護力： 我們不僅追蹤了針對原始株的探討，更針對具高度突變的變異株（如 BA.5 和 JN.1）進行了中和及結合抗體的分析。
  • 加強劑效應：抗體水平在接種後續加強劑（特別是第四、第五和第六劑）後達到了極高值，證明免疫系統對重複接種加強劑仍能保持高度反應。
  • 疫苗效能表現： 儘管科興疫苗（CoronaVac）引發較低的絕對抗體水平低於復必泰（BNT162b2），但獨立數據證實其在預防感染及重症方面仍維持高度有效性。

抗體減弱趨勢與混合免疫成效

圖 2C 描繪了新冠病毒免疫力的一項關鍵現實：抗SARS-CoV-2抗體會隨時間呈一定程度的下降，這在接種科興疫苗後的 3 至 6 個月內尤為明顯。然而，數據亦顯示了由自然突破性感染所產生的抗體反應，通常更強、結構更多元，且具更長久的保護效益。透過與衞生當局分享本研究的發現，本隊列研究直接促成了政府於2021年尾建議接種第三劑新冠疫苗的決策，從而直接保護更廣泛的香港社區。

圖2. 本研究隊列參加者的【A】疫苗接種史；【B】疫苗免疫原性；及【C】接種 COVID-19 疫苗後抗SARS-CoV-2抗體隨時間減弱的趨勢
圖2. 本研究隊列參加者的【A】疫苗接種史；【B】疫苗免疫原性；及 【C】接種 COVID-19 疫苗後抗SARS-CoV-2抗體隨時間減弱的趨勢

未來研究方向

閣下所提供的血液樣本，將持續作為一份極具價值的科學資源。我們正在分析本研究所收集的樣本及數據，並正準備發表以下相關論文：接續加強劑後的疫苗有效性，混合免疫（疫苗及自然感染）效應，不同疫苗接種與感染史下的再次感染率，及首次感染與再次感染後抗體動態變化的模式 。

感謝閣下過去六年參與本研究的跟進，我們衷心感謝 閣下的支持！

參考文獻

  1. Lim WW, Mak L, Ho F, et al. Seroprevalence of COVID-19 among healthcare workers in Hong Kong during the first 2 years of the COVID-19 pandemic (2020–2021): a longitudinal cohort study. BMJ Open 2026; 16: e110192. [鏈接]
  2. Lim WW, Mak L, Leung GM, Cowling BJ, Peiris M. Comparative immunogenicity of mRNA and inactivated vaccines against COVID-19. Lancet Microbe 2021; 2: e423. [鏈接]
  3. Yang B, Lin Y, Xiong W, et al. Comparison of control and transmission of COVID-19 across epidemic waves in Hong Kong: an observational study. Lancet Reg Health West Pac 2024; 43: 100969. [鏈接]
  4. Leung NHL, Cheng SMS, Cohen CA, et al. Comparative antibody and cell-mediated immune responses, reactogenicity, and efficacy of homologous and heterologous boosting with CoronaVac and BNT162b2 (Cobovax): an open-label, randomised trial. Lancet Microbe 2023; 4: e670–82. [鏈接]
  5. McMenamin ME, Nealon J, Lin Y, et al. Vaccine effectiveness of one, two, and three doses of BNT162b2 and CoronaVac against COVID-19 in Hong Kong: a population-based observational study. Lancet Infect Dis 2022; 22: 1435–43. [鏈接]