Immunogenicity and Safety of a Single Dose of mRNA SARS-CoV-2 Vaccine in Chinese Adults With Hybrid Immunity

This is a multicentre post-marketing cohort study to evaluate the immunogenicity and safety of a single dose of mRNA SARS-CoV-2 vaccine SYS6006 in Chinese adults predominantly with hybrid immunity. A total of 2,052 adults aged 18 years and older who received one dose of SYS6006 were monitored for serious adverse events (SAEs) for 6 months. The first 60 participants comprised an immunogenicity subgroup, with blood samples collected before vaccination and at day 14, month 3, and month 6 post-vaccination to assess humoral and cellular immune responses.

Inclusion Criteria: 1. Adults aged 18 years and over, including the elderly over 60 years and those with general underlying diseases. 2. At least 4 months since the last SARS-CoV-2 infection (or never infected), and at least 6 months since the last COVID-19 vaccination. 3. Able and willing to comply with the study procedures and to provide written informed consent. Exclusion Criteria: 1. Suspected COVID-19 symptoms on the day of enrollment (e.g., dry/sore throat, cough). 2. Positive SARS-CoV-2 antigen rapid test at enrollment. 3. Prior receipt of the first COVID-19 booster dose . 4. History of severe adverse reactions or anaphylaxis related to vaccination, or known severe allergy to any vaccine component. 5. Pregnant or lactating women. 6. Any other condition that, in the investigator's judgment, makes the individual unsuitable for the study. \-