Abstract
Studies of myocarditis/pericarditis following mRNA COVID-19 vaccines in Hong Kong have been published. Data are consistent with data from other active surveillance or healthcare databases. The mRNA COVID-19 vaccines have been shown to rarely increase risk of myocarditis, with the highest risk among males aged 12-17 after the second dose. An increased risk of pericarditis has also been shown after the second dose, though less common than myocarditis and more evenly distributed among different sex and age groups. Because of the increased risk of post-vaccine myocarditis, Hong Kong implemented a single dose mRNA COVID-19 vaccine policy on September 15, 2021 for adolescents (age 12-17 years). Post-policy, there were no cases of carditis. 40,167 first dose patients did not receive a second dose. This policy was highly successful in the reduction of carditis, but the trade-off is the potential risk of disease and cost to population-level immunity. This commentary brings forward some important global policy considerations.