The risk of household spread of SARS-CoV-2 hinges on both the transmission dynamics of the virus circulating in the community as well as the seroprotection pattern of constituent members, which can be attributed to vaccination and previous infections. This study is conceptualised to assess the dynamicity of SARS-CoV-2 risk at the household level, through monitoring the pattern of seroprotection, in conjunction with the vaccination coverage, history of infection and exposure risk in the setting of Hong Kong.

The aim of this study is to assess the SARS-CoV-2 risk at the household level, with the objectives of (a) determining the coverage of vaccination and its changes over time; (b) monitoring pattern of exposure and history of infection; and (c) evaluating the level of seroprotection and its longitudinal trend.

A cohort of households comprising 900 persons would be recruited. Invited participants would be attend the Research Centre for blood sampling and the completion of a simple questionnaire at 3 different timepoints at 12-18 months apart. A questionnaire would be administered to capture the following characteristics: (a) Socio-demographics; (b) History of SARS-CoV-2 infection; (c) adoption of precautionary measures; (d) SARS-CoV-2 testing history and (e) SARS-CoV-2 vaccination uptake.

Participants would be tested for SARS-CoV-2 serology. The main markers for measurement are nucleocapsid antibody for inferring past infection, spike antibody for the immunological responses, and seroprotection by SARS-CoV-2 surrogate virus neutralisation test.

Inclusion Criteria:

• adults of age 18 or above, or children under the age of 18 with informed consent of the legal guardian
• normally residing in Hong Kong
• could communicate in spoken and written Chinese and/or English

Exclusion Criteria:

• individuals with mental illness
• prisoners

Adults of households enrolling in a population cohort covering residents from all 18 districts in Hong Kong.