This is an observer blind randomized controlled trial study to evaluate the humoral immunogenicity profile - neutralizing antibody - after 28 days following vaccination with Vaksin Merah Putih - UA SARS-CoV-2 (Vero Cell Inactivated) vaccine as heterologue booster compared with CoronaVac administered intramuscularly in healthy adults age 18 year and above.

Vaksin Merah Putih - UA SARS-CoV-2 (Vero Cell Inactivated) vaccine is an inactivated vaccine made of SARS-CoV-2 virus isolated from a patient in Surabaya, composed with aluminium hydroxy gel, tween 80, and L-histidine, and this will be the first booster study in human.

This is an observer blind randomized controlled trial. There will be 2 groups in the study. First group will receive CoronaVac vaccine, manwhile the other group will receive Vaksin Merah Putih - UA SARS-CoV-2 (Vero Cell Inactivated) vaccine. The inclusion and exclusion criteria for the subjects were listed below. All subjects will receive either one dose of CoronaVac or Vaksin Merah Putih - UA SARS-CoV-2 (Vero Cell Inactivated) vaccine and be followed for 6 months. The vaccine will be administered intramuscularly.

This study will have one interim and one full analysis reports. The main focus is immunogenicity and safety issues.

Data Safety Monitoring Board will be commissioned for this study to evaluate safety data over the study period and to review any events that meet a specific study pausing rule or any other safety issue that may arise. They will review the blinded 7 and 28 days safety data following the vaccine, and then the 3 and 6 months safety data. The immunogenicity data will be evaluated until 6 months.

Inclusion Criteria:

1. Healthy adults and elderly, males and females, 18 years of age and above. Healthy status will be determined by the investigator based on medical history, clinical laboratory results, vital sign measurements, and physical examination at screening.
2. Subjects already received 2 (two) doses of CoronaVac inactivated vaccines at least 6 months prior to this study.
3. Subjects have been informed properly regarding the study and signed the informed consent form
4. Subject will commit to comply with the instructions of the investigator and the schedule of the trial
5. Female subjects of childbearing potential must agree to consistently use any methods of contraception (except the periodic abstinence) from at least 21 days prior to enrollment and through 6 months after the vaccination.
6. Participants agree not to donate bone marrow, blood, and blood products from the vaccine administration until 3 months after receiving the vaccine.
7. Participants must be willing to provide verifiable identification, has means to be contacted and to contact the investigator during the study.

Exclusion Criteria:

1. Subjects concomitantly enrolled or scheduled to be enrolled in another vaccine trial
2. Evolving mild, moderate, and severe illness, especially infectious diseases or fever (axillary temperature 37.5oC or more) concurrent or within 7 days prior to study vaccination. This includes respiratory or constitutional symptms consistent with SARS-CoV-2 (cough, sore throat, difficulty in breathing, etc)
3. Known history of allergy to any component of the vaccines
4. History of uncontrolled coagulopathy or blood disorders contraindicating intramuscular injection
5. Any autoimmune or immunodeficiency disease/condition
6. Subjects who have received in the previous 4 weeks a treatment likely to alter the immune response (intravenous immunoglobulin, blood derived products, long term corticosteroid - more than 2 weeks, and so on), OR anticipation of the need for immunosuppressive treatment within 6 months after last vaccination. The use of topical or nasal steroid will be permitted. Inhaled glucocorticoids are prohibited.
7. Unstable chronic disease, inclusive of uncontrolled hypertension, congestive heart failure, chronic obstructive pulmonary disease, asthma, chronic urticaria, diabetes requiring use of medicine. The final decision regarding this condition will be decided by the attending field clinicians or investigator.
8. Any abnormality or chronic disease which according to the investigator might interfere with the assessment of the trial objectives
9. Individuals who previously receive any booster vaccine against Covid-19.
10. Individuals who have a previously ascertained Covid-19 in the period of 1 month (for mild, moderate, or asymptomatic people) or 3 months (for severe Covid-19) before the recruit of this study, or in a close contact in the last 14 days with confirmed case of Covid-19.
11. Positive test for SARS-CoV-2 (Antigen or PCR) at screening prior to the vaccination. Testing may be repeated during the screening period if exposure to positive confirmed case of SARS-CoV-2 is suspected, at the discretion of investigator.
12. History of alcohol or substance abuse
13. HIV patients.
14. Malignancy patients within 3 years prior to study vaccination.
15. Any neurological disease or history of significant neurological disorder such as meningitis, encephalitis, Guillain-Barre Syndrome, multiple sclerosis, etc
16. Vital sign abnormalities and clinical laboratory abnormalities as decided by the investigators. Vital sign measurements and clinical laboratory testing may be repeated before the final decision.
17. Women who are pregnant or who plan to become pregnant during the study.
18. Participant has major psychiatric problem or illness
19. Participant cannot communicate reliably with the investigator
20. Participant has contraindication to intramuscular injection and blood draws, such as bleeding disorders or phobia.
21. Participant had major surgery within 12 weeks before vaccination which will not be fully recovered, or has major surgery planned during the time participant is expected to participate in the study or within 6 months after the last dose of study vaccine administration.
22. Any condition that in the opinion of the investigators would pose a helath risk to the subject if enrolled or could interfere with the evaluation of the vaccine or interpretation of the study results
23. Study team members.
24. Subject planning to move from the study area before the end of study period.

This is an observer blind randomized controlled trial. There will be 2 groups in the trial. All subjects will have either CoronaVac or Vaksin Merah Putih - UA SARS-CoV-2 (Vero Cell Inactivated) vaccine as booster injection. There will be 350 subjects in the study.