Introduction
death, illness, coronavirus disease 2019
CORONAVIRUS DISEASE 2019
On 30 January 2020, the World Health Organization declared that the coronavirus disease 2019 (COVID-19) outbreak constituted a public health emergency of international concern (Studies in Canada, Singapore, and other countries have shown that a second booster immunization provides additional protection against COVID-19 and reduces severe illness and death (On 7 December 2022, the Chinese government issued the “New ten measures” as an adjustment to its “Twenty measures” COVID-19 prevention and control policy released on 11 November 2022 (This parallel-controlled prospective cohort study aimed to investigate antibody levels and breakthrough infection after a fourth immunization dose of Ad5-nCoV or inactivated SARS-CoV-2 vaccine.