Efficacy and Safety of Oral Lactobacillus Plantarum GUANKE (CGMCC NO.21720) in Enhancement of Antibody Level After SARS-CoV-2 Vaccination (Trial 2)

Inclusion Criteria: 1. 18 ≤age ≤59 years; 2. Vaccinated with two doses of SARS-CoV-2 vaccine (manufactured by Sino Biopharmaceutical Limited or SINOVAC BIOTECH CO., LTD.) (≥6 months from the time of vaccination). 3. Plan to vaccinate third dose vaccination (manufactured by Sino Biopharmaceutical Limited or SINOVAC BIOTECH CO., LTD.); 4. Voluntarily participate in the study with signed informed consent form. Exclusion criteria: 1. Pregnancy or lactation period; 2. Infected with human immunodeficiency virus (HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV); 3. History of autoimmune diseases (e.g. rheumatoid arthritis, systemic lupus erythematosus, dry syndrome, etc.); 4. Previously infected with SARS-CoV-2 or close contact of SARS-CoV-2 infected individual; 5. Other SARS-CoV-2 vaccination history (not manufactured by Sino Biopharmaceutical Limited or SINOVAC BIOTECH CO., LTD.); 6. End-stage cancer or other terminal diseases with life expectancy \<6 month; 7. History of severe cardiovascular and cerebrovascular diseases, such as heart failure, uncontrolled coronary heart disease, cardiomyopathy, uncontrolled arrhythmia, or history of myocardial or cerebral infarction within past six months; 8. Participating in other clinical trials.