Recombinant COVID-19 Vaccine for nasal use (CanSino Biotech)

This is a multicenter, parallel groups, partially randomized, open-label, blank-controlled adaptive platform study to evaluate the effectiveness of a second COVID-19 vaccine booster in Chinese adults who are charactered as the majority of whom with hybrid immunity of COVID-19 vaccination and COVID-19 breakthrough infection. Individuals aged 18 years and over, include the elderly over 60 years old or those with underlying diseases (history of underlying medical conditions diagnosed by a clinician, including hypertension, diabetes, heart disease, etc). The eligible participants with an interval ≥ 4 months after previous SARS-CoV-2 infection (or had never been infected) and ≥ 6 months from the first COVID-19 vaccine booster will be recruited. Participants who are not willing to receive the second booster but are consent to participate the surveillance for COVID-19, will be included as a blank control. Informed consent will be acquired from eligible participants. Other participants who are willing to receive the second booster and participate the surveillance for COVID-19, will be randomly allocated in a ratio of 1: k (k is the number of vaccine types) to the different investigational vaccines, stratified according to age and history of COVID-19 infection. The symptomatic COVID-19 cases will be reported and documented in both the investigational and control groups. The occurrence of serious adverse events within 6 months after vaccination will be observed. Moreover, blood and nasal mucosa samples will be collected on the day 0 before and day 14, month 3 and 6 after the booster vaccination in a subgroup for humoral, cellular and mucosal immunogenicity analysis. Moreover, oral specimens will be collected once for all participants on the day of enrollment.