1. Aged between 18 and 60 years, 2. Able to understand the content of informed consent and willing to sign the informed consent, 3. Able and willing to complete all the secluded study process during the whole follow-up period of 6 months. 4. Negative in HIV diagnostic test, 5. Negative in serum antibodies (IgG and IgM) screening of COVID-19. 6. Normal in lung CT images (no imaging features of COVID-19), 7. Axillary temperature <=37.0 degree C, 8. The BMI index 18.5-30.0, 9. Negative in Nasopharyngeal swabs / sputum and anal swabs through RTPCR, 10. Laboratory tests such as hematological examination and clinical biochemistry examination are in the normal range or without meaning judged by clinical doctor, 11. General good health as established by medical history and physical examination.

1. Aged between 18 and 60 years, 2. Able to understand the content of informed consent and willing to sign the informed consent, 3. Able and willing to complete all the secluded study process during the whole follow-up period of 6 months. 4. Negative in HIV diagnostic test, 5. Negative in serum antibodies (IgG and IgM) screening of COVID-19. 6. Normal in lung CT images (no imaging features of COVID-19), 7. Axillary temperature <=37.0 degree C, 8. The BMI index 18.5-30.0, 9. Negative in Nasopharyngeal swabs / sputum and anal swabs through RTPCR, 10. Laboratory tests such as hematological examination and clinical biochemistry examination are in the normal range or without meaning judged by clinical doctor, 11. General good health as established by medical history and physical examination.