Abstract
We conducted a multicenter, partially randomized, platform trial to assess the effectiveness of a booster dose of an aerosolized or intramuscular adenovirus type 5 vectored COVID-19 vaccine (Ad5-nCoV) in Chinese adults (NCT05855408). Between May 23, 2023, and August 28, 2023, 4089 eligible participants were equally randomized to receive either a booster dose of aerosolized Ad5-nCoV via oral inhalation at 0.1 mL (IH Ad5-nCoV, n = 2039) or an intramuscular injection of Ad5-nCoV at 0.5 mL (IM Ad5-nCoV, n = 2050). Additionally, 2008 participants who declined the booster but consented to participate in COVID-19 surveillance were enrolled in the control group. All participants were monitored for symptomatic COVID-19 over a six-month surveillance period for the primary outcome. From 14 days after the vaccination, 14 (15/1000 person-years), 19 (20/1000 person-years), and 34 (37/1000 person-years) COVID-19 cases were confirmed in the IH Ad5-nCoV group, the IM Ad5-nCoV group, and the control group, respectively, which resulted in an adjusted effectiveness of 52.3% (95% CI 10.4 to 74.6) for IH Ad5-nCoV and 37.2% (95% CI -11.2 to 64.5) for IM Ad5-nCoV. The IH Ad5-nCoV booster was associated with a lower incidence of symptomatic COVID-19, but there is no solid evidence that IH Ad5-nCoV was more effective than IM Ad5-nCoV.