This is a study trial to assess the effectiveness of the immune response stimulated by the genetically engineered Bacillus subtilis spore extract which contain Spike protein of the SARS-COV2 on the spore coat.

COVID-19 immunization reduces the risk of COVID-19 and potentially serious complications. In clinical trials, all COVID-19 vaccines currently authorized for use in the United States are beneficial in protecting adults and children 5 years and older against COVID-19, including severe illness. So far, studies looking at how COVID-19 vaccines work in real-world conditions (vaccine effectiveness studies) have shown that they work well. However, it has been reported that most of the antibodies in people who received the second dose of COVID-19 vaccine had been dramatically decreased.

Bacillus subtilis (B. subtilis) is a generally regarded as safe organism and it is a common food source. The investigators have used an engineered Bacillus subtilis spore which express and display the spike protein receptor binding domain (sRBD) of the SARS-CoV-2 on the surface. The investigators have proved that it successfully increased the neutralizing antibody against sRBD in unvaccinated mice and human individuals after oral administration.

On this basis, the investigators designed and developed an oral antibody booster by extracting the spore surface of B. subtilis. This supplement has the advantage of being stable and effective, free of recombinant plasmid, and can be served as a potential antibody booster to existing vaccines.

Mice toxicity and efficacy test was conducted and the experiment proved that the B. subtilis spores extract was effective in inducing immune response, and it was safe and did not cause any significant adverse effect.

The B. subtilis spore extract will be further studied in a human trials through oral administration to test its safety and the immune effect resulted in human body.

Inclusion Criteria:

• healthy
• age over 12 years
• the outcome of the following examinations should be clinically insignificant: medical and surgical history (hypo-, hypertension, allergy, other diseases, major surgery, micturition, defecation, sleep, illness within the last 4 weeks prior to the start of the trial);
• participant vaccinated with COVID-19 over 6 months
• anti-SARS CoV 2 neutralizing antibody is negative in serum.

Exclusion Criteria:

• pregnant women
• history of COVID-19 infection or showing COVID-19 infection symptoms
• having had contact to people with known COVID-19 infection in the last 14 days
• having fever (> 37.4oC in the last 24 hours), dry cough or feeling tired and having aches and pains, nasal congestion, runny nose, sore throat and diarrhea.
• positive real time RT-PCR COVID-19 test.
• persons with autoimmune diseases
• allergic diathesis or any clinically significant allergic disease (i.e. asthma)
• any condition that might impair the immune response
• recent or current immunosuppressive medication
• any other vaccine application 5 months before the first dose