Study participants
MAY
Between May 14 and 27, 2022, 211 volunteers aged 18–80 years who had received three doses of inactivated vaccine (CoronaVac or Covilo) ≥ 6 months earlier were recruited and screened for eligibility for this phase 4 trial. A total of 201 participants, including 120 adults (18–59 years) and 81 older individuals (60–80 years), were sequentially enrolled and randomly assigned to groups. One individual withdrew consent after randomization. In all, 200 participants received either a fourth dose of Ad5-nCoV (treatment group, 