Heterologous Prime-boost Immunization with an Aerosolised Adenovirus Type-5 Vector-based COVID-19 Vaccine (Ad5-nCoV) After Priming with an Inactivated SARS-CoV-2 Vaccine

This is a randomized, open-label, parallel-controlled study to evaluate the safety and immunogenicity of heterologous prime-boost immunization with an aerosolised adenovirus type-5 vector-based COVID-19 vaccine (Ad5-nCoV) after priming with an inactivated SARS-CoV-2 vaccine in adults at 18 years of age or above. 420 healthy subjects aged over or equal to 18 years whom have received two doses of inactivated SARS-CoV-2 vaccines within the last 3\~9 months, will be recruited in this study. Eligible participants will be randomized at a 1:1:1 ratio to receive a booster dose of inactive SARS-CoV-2 vaccine or a low dose of aerosolized Ad5-nCoV or a high dose of aerosolized Ad5-nCoV. The occurrence of adverse events within 28 days and serious adverse events within 6 months after vaccination will be observed. In addition, blood samples will be collected on the day 0 before and day 7, 14, 28 and month 3, 6, and 12 after the booster vaccination. Each subject will remain in this study for approximately 13 months.