Subjects who fall into any of the following criteria are excluded from participating in the study:1. Obese subjects (BMI >= 30 kg/m2)2. Subjects who have strong dyspnea, chest pain, or bloody sputum3. Subjects with history of COVID-194. Subjects who are being treated or will be treated by neutralizing antibody preparations5. Subjects who are being treated by immunosuppressive agents, antirheumatic agents, corticosteroids, or immunoglobulin preparations at giving their consent6. Subjects who are administered intestinal regulators orally7. Subjects who are taking one or more beverage or foods that contain Lactococcus lactis strain Plasma or yogurt (that contain lactic acid bacteria or Lactobacillus bulgaricus) everyday8. Subjects who are pregnant, possibly pregnant, or breastfeeding9. Subjects who are participating in other clinical trials at giving their consent10. Subjects who need legal representative for giving consent11. Subjects with other conditions that the responsible investigator or subinvestigators think inappropriate to participate in the study

Subjects who fall into any of the following criteria are excluded from participating in the study:1. Obese subjects (BMI >= 30 kg/m2)2. Subjects who have strong dyspnea, chest pain, or bloody sputum3. Subjects with history of COVID-194. Subjects who are being treated or will be treated by neutralizing antibody preparations5. Subjects who are being treated by immunosuppressive agents, antirheumatic agents, corticosteroids, or immunoglobulin preparations at giving their consent6. Subjects who are administered intestinal regulators orally7. Subjects who are taking one or more beverage or foods that contain Lactococcus lactis strain Plasma or yogurt (that contain lactic acid bacteria or Lactobacillus bulgaricus) everyday8. Subjects who are pregnant, possibly pregnant, or breastfeeding9. Subjects who are participating in other clinical trials at giving their consent10. Subjects who need legal representative for giving consent11. Subjects with other conditions that the responsible investigator or subinvestigators think inappropriate to participate in the study