An international research team from the University of Hong Kong, the Laboratory of Data Discovery for Health, and the Centre for Immunology & Infection collaborated with the Hong Kong Red Cross Blood Transfusion Service to estimate vaccine effectiveness against Omicron infections. They found that three doses of Comirnaty or CoronaVac were 48% or 30% effective in preventing Omicron infection shortly after vaccination, improving after a fourth dose. However, vaccine effectiveness waned rapidly over 100 days. The researchers also estimated that over 45% of the Hong Kong population was infected between 1 January and 31 July 2022.