Safety and Immunogenicity of Inactivated Heterologous Booster Vaccination

Inclusion Criteria:

1. Participants of either gender aged 18 years and older at screening
2. Participants who have received two doses of an inactivated Covid vaccine and no booster. Primary series with an inactivated vaccine had to be completed at least 6 months prior to enrollment.
3. Participants must have read, understood, and signed the informed consent form (ICF)

4. Medically stable such that, according to the judgment of the investigator, hospitalization within the study period is not anticipated and the participant appears likely to be able to remain on study through the end of protocol-specified follow-up.

   a. A stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 3 months prior to the expected day of booster vaccination.

5. Participant has a Body Mass Index (BMI) of 18.0-30.0 kg/m2, inclusive, at screening (Visit 0).
6. Must be able to attend all visits of the study and comply with all study procedures, including daily completion of the e-diary for 7 days following each vaccination.

7. Women of childbearing potential (WOCBP), who are sexually active with a man, must be able and willing to use at least 1 highly effective method of contraception (i.e. implant contraceptive, intra-uterine device (IUD) containing either copper or levonorgestrel, male sterilization [vasectomy], female sterilization, injectable contraceptive, oral contraceptive pill, vaginal contraceptive ring, barrier type of birth control measure) from study start until a minimum of 3 months after receiving the booster vaccine.

   1. A female participant is considered to be a WOCBP after menarche and until she is in a postmenopausal state for 12 consecutive months (without an alternative medical cause) or otherwise permanently sterile.
   2. Note: Participants not of childbearing potential are not required to use any other forms of contraception during the study. Non-childbearing potential is defined as participant confirmed:
   3. Surgical sterilization for ≥3 months prior to Visit 1 (e.g., bilateral oophorectomy, bilateral salpingectomy, bilateral occlusion by cautery, hysterectomy, or tubal ligation).
   4. Postmenopausal (defined as permanent cessation of menstruation for at least 12 consecutive months prior to screening).
8. WOCBPs must have a negative pregnancy test prior to the booster vaccination.
9. Has received a second dose of licensed inactivated COVID-19 vaccine 6 to 15 months before study vaccination.

Exclusion Criteria:

1. Known history of natural SARS-CoV-2 infection (based on medical history and/or confirmed either by PCR or rapid antigen test) less than four months prior to the planned booster vaccination..
2. Participant is pregnant or planning to become pregnant within 3 months after booster administration.
3. History of allergy to any component of the vaccine.
4. Participant had close contact to persons with confirmed SARS-CoV-2 infection within 30 days prior to screening (Visit 0).
5. Participant has participated in a clinical study involving an investigational SARS-CoV-2 vaccine or has received or plans to receive a licensed SARS-CoV-2 vaccine during the duration of the study.
6. Significant infection or other acute illness, including fever > 100 °F (> 37.8 °C) within 48 hours before vaccination.
7. Positive SARS-CoV-2 rapid Antigen test result during screening (Visit 0) or Visit 1.

8. Participant has a known or suspected defect of the immune system, such as participants with congenital or acquired immunodeficiency, including infection with HIV, status post organ transplantation or immuno-suppressive therapy within 4 weeks prior to the expected day of vaccination (Visit 1).

   • Immuno-suppressive therapy is defined as administration of chronic (longer than 14 days) prednisone or equivalent ≥ 0.05 mg/kg/day within 4 weeks prior to the expected day of first vaccination (visit 1), radiation therapy or immunosuppressive cytotoxic drugs/ monoclonal antibodies in the previous 3 years; topical and inhaled steroids are allowed.
   • Participants with chronic HIV unless: HIV disease with documented viral load <50 copies/ml and CD4 count >200 cells/mm3 for at least 6 months before first vaccination, and stable antiretroviral therapy for the last 6 months.
9. Participant has a history of malignancy in the past 5 years other than squamous cell or basal cell skin cancer. If there has been surgical excision or treatment more than 5 years ago that is considered to have achieved a cure, the participant may be enrolled. A history of hematologic malignancy is a permanent exclusion. Participants with a history of skin cancer must not be vaccinated at the previous tumor site.
10. History of drug dependency or current use of drug of abuse or alcohol abuse at screening.
11. Significant blood loss (> 450 mL) or has donated 1 or more units of blood or plasma within 6 weeks prior to the expected day of first vaccination (Visit 1).
12. History of clinically significant bleeding disorder (e.g., factor deficiency, coagulopathy, or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venipuncture.
13. Severe and uncontrolled ongoing autoimmune or inflammatory disease, History of Guillain-Barre syndrome or any other demyelinating condition.
14. Any other significant disease, disorder or finding which in the opinion of the investigator may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study.