Effectiveness of CoronaVac and BNT162b2 Vaccines Against Severe Acute Respiratory Syndrome Coronavirus 2 Omicron BA.2 Infections in Hong Kong

There is limited evidence on vaccine effectiveness against asymptomatic or mild Omicron infections. We estimated that recent third doses of messenger RNA or inactivated vaccines reduced the risk of self-reported infection by 52% (95% confidence interval, 17%-73%) among randomly sampled adults during the Omicron BA.2-dominated surge in Hong Kong. Using self-reported vaccination and testing results for coronavirus disease 2019 among a random adult population in Hong Kong, we estimated that third doses of messenger RNA or inactivated vaccines could provide moderate level of protection during the Omicron BA.2 surge.