Initial Two Doses of COVID-19 Vaccine mRNA-1273 for an Individual Previously Vaccinated with Two Doses of an Inactivated Vaccine CoronaVac That Has Not Been Approved in Japan

The inactivated coronavirus disease 2019 vaccine CoronaVac has not been approved in Japan. Little information is available on cases in Japan in which an approved mRNA vaccine was administered as the initial (first or second) dose after two doses of CoronaVac. Furthermore, the safety and efficacy of this combination are not established. We here evaluated the safety and efficacy in a patient who showed an antibody response to an approved vaccine, mRNA-1273, after a previous vaccination with CoronaVac. The adverse events consisted of only mild local and systemic common reactions and were transient. In addition, a strong and persistent antibody response was observed.