A GP in Hong Kong is attempting to study this across 1000 people, which is only marginally fewer than the number of cases in Hong Kong as of today (1013 confirmed cases): https://www.otandp.com/blog/estimating-the-longitudinal-sero...

Hong Kong government is also measuring the real time effective reproduction number: https://chp-dashboard.geodata.gov.hk/covid-19/en.html (click on the arrows at the bottom to scroll left and right through various dashboards)