Safety and Immunogenicity of Recombinant COVID-19 Vaccine (Sf9 Cell) as a Booster

A phase Ⅱ, observer-blind, randomized, controlled, investigator-initiated clinical trial to evaluate the safety and immunogenicity of a booster vaccination with Recombinant COVID-19 vaccine (Sf9 Cell) in a population aged 18 years and above who have completed homologous primary vaccination with either Inactivated or mRNA or Viral Vector COVID-19 vaccines at least 6 months prior to enrolment. The study uses a non-inferiority design to compare between schedules with Recombinant COVID-19 Vaccine (Sf9 Cell) versus COVID-19 Vaccine (Vero Cell), Inactivated as the booster dose. Participants, laboratory and analysing statisticians will remain blind to treatment allocation. A total of 450 participants will be enrolled (participants aged ≥ 60 years account for approximately 10%), consisting of 3 cohorts: 150 participants who received 2 doses of Inactivated COVID-19 vaccines with the second dose at least 6 months (≥180 days) prior to enrolment. 150 participants who received 2 doses of mRNA COVID-19 vaccines with the second dose at least 6 months (≥180 days) prior to enrolment. 150 participants who received 2 doses of Viral Vector COVID-19 vaccines with the second dose at least 6 months (≥180 days) prior to enrolment. Each of 3 cohorts of 150 participants will be randomized 1:1 to receive a single dose of Recombinant COVID-19 vaccine (Sf9 Cell) (test group) or the COVID-19 Vaccine (Vero Cell), Inactivated (control group).