Study design and participants
anaphylaxis, fever, laboratory-confirmed SARS-CoV-2 infection, neurologic illness, hypertension, diabetes
ADVERSE REACTIONS, RESPIRATORY DISEASE, ANAPHYLAXIS, CARDIOVASCULAR DISEASE, CORONAVIRUS, HYPERTENSION, DISEASE, DIABETES
We performed a single-center, randomized, double-blind, parallel-controlled trial of a fourth vaccine dose with heterologous booster (Ad5-nCoV) or homologous booster (inactivated SARS-CoV-2 vaccine) in a population that had completed a three-dose inactivated SARS-CoV-2 vaccine regime in Hangzhou, Zhejiang Province, China. Healthy participants aged 18–80 years with stable medical conditions were recruited from the community and divided into groups of younger adults (aged 18–59 years) and older adults (aged 60–80 years) at a 2:1 ratio. All participants had received three doses of inactivated vaccine (the third dose was CoronaVac or Covilo) 6 months before the screening visit.The exclusion criteria included a history of laboratory-confirmed SARS-CoV-2 infection (based on the epidemic information system in China); pregnant or lactating women; new onset of fever; an immunosuppressive condition; previous vaccination with any other authorized vaccine within 28 days before screening (or the intention to receive such a vaccine within 14 days after the booster dose); history of severe adverse reactions (e.g., anaphylaxis) to adenovirus-vectored vaccines or coronavirus vaccines; administration of (or the intention to receive) any blood, plasma, or immunoglobulin products within 90 days before screening; participants with severe and/or uncontrolled cardiovascular disease, respiratory disease, hypertension (systolic pressure ≥180 mmHg/ diastolic pressure ≥110 mmHg), diabetes, or neurologic illness; and any special circumstances that researchers considered may increase the risk of individuals participating in the study or interfere with the evaluation of the initial objectives of the study.All participants signed the informed consent form before enrollment. The trial protocol was reviewed and approved by the Research Ethics Committee of the Zhejiang Provincial Center of Disease Control and Prevention, and no changes were made after the initiation of the study (ethics code number: 2022-021-01). The trial was prospectively registered with 