# Seroprevalence of COVID-19 in healthcare workers in Hong Kong: a longitudinal cohort study

Canonical HTML URL: https://hcw.sph.hku.hk/

Languages: English and Traditional Chinese.

## Study status

The study was completed in June 2026. The site publishes the final report and study findings.

- [Download the final bilingual report (PDF)](https://hcw.sph.hku.hk/downloads/20260611_hcw_summary_final_bilingual.pdf)

## Study overview

The HKU School of Public Health established this prospective cohort study in 2020 among healthcare workers in Hong Kong. The study estimated SARS-CoV-2 antibody seroprevalence, evaluated COVID-19 vaccine immunogenicity and effectiveness, and assessed how long vaccination- and infection-induced protection lasted.

The cohort enrolled 1,752 participants and collected 16,875 blood samples. The study was led by Professor Benjamin Cowling and supported by the Health and Medical Research Fund of the Hong Kong Health Bureau.

## Participant information

The public page records the study's participant information, including eligibility for full-time healthcare workers in Hong Kong, regular health follow-up, blood-sample collection, vaccine sub-studies, participation steps, and data confidentiality. Participation was voluntary and the study team could be contacted at [hcwsero@hku.hk](mailto:hcwsero@hku.hk).

## Findings

### COVID-19 epidemiology in Hong Kong healthcare workers

Fewer than 1% of participating healthcare workers had been infected by December 2021. The study mapped SARS-CoV-2 epidemiology among healthcare workers across several phases of the pandemic.

### Vaccination and immune responses

Participants received up to eight COVID-19 vaccine doses during the six-year period. The study measured antibody responses to mRNA and inactivated vaccines and found strong responses to repeated booster doses.

### Antibody waning and hybrid immunity

Anti-SARS-CoV-2 antibodies declined over time, particularly within three to six months after CoronaVac vaccination. Natural breakthrough infection generally produced stronger and longer-lasting antibody responses.

### Ongoing analysis

The research team continues to analyze vaccine effectiveness after successive booster doses, hybrid immunity, reinfection rates, and antibody dynamics after infection and reinfection.

## Selected references

- [Seroprevalence of COVID-19 among healthcare workers in Hong Kong during the first 2 years of the COVID-19 pandemic](https://pubmed.ncbi.nlm.nih.gov/42152443/)
- [Comparative immunogenicity of mRNA and inactivated vaccines against COVID-19](https://pubmed.ncbi.nlm.nih.gov/34308395/)
- [Comparison of control and transmission of COVID-19 across epidemic waves in Hong Kong](https://pubmed.ncbi.nlm.nih.gov/38076326/)