There is evidence that some types of probiotics play a role in alleviation of symptoms of acute respiratory tract infections and bursting immune response to respiratory and enteric viruses. Available data serves a rationale for the study exploring a role of nutritional support with probiotics in adult outpatients with COVID-19. Hypothesis of the study is that a proposed mixture of lactobacilli and bifidobacteria facilitate faster recovery from COVID-19 and enhance specific immune response to SARS-CoV-2 antigens.

One hundred adults with confirmed (PCR or antigen test) symptomatic COVID-19 lasting upto 5 days will be screened for the study. When the subject meets enrollment criteria, he/she will be randomized to take an investigational product (probiotic, test dietary supplement, TDS), a mixture of lactobacilli and bifidobacteria or placebo 1 time a day before breakfast for 28 days after enrollment. During observation, the patient will keep Respiratory Illness Diary. Blood serum will be collected at baseline, day 0-5 (Nurse Visit 1), after 28-35 days (Nurse visit 2), and 6 months (Nurse visit 3) for evaluation of anti-SARS-CoV-2 antibodies to nucleocapsid and spike antigents. In 3 months, investigator/family physician will collect Post-COVID-19 Questionnaire

Inclusion Criteria:

1. Age ≥ 18 - ≤ 65 years;
2. Male or non-pregnant female;
3. Informed virtual pre-consent and paper signed consent forms;
4. Confirmed symptomatic COVID-19 lasting 0-5 days;
5. Subject understands and agrees to comply with study procedures including triple blood analysis for anti-SARS-CoV-2 IgG;

Exclusion Criteria:

1. Risk for the complicated course of COVID-19 due to:

   1.1. Hypertension; 1.2. Diabetes mellitus; 1.3. Immunosuppressive conditions; 1.4. Chronic pathology of the respiratory system ; 1.5. Chronic pathology of the cardiovascular system ; 1.6. Malignant tumor ; 1.7. Systemic inflammatory connective tissue disease ; 1.8. Cerebrovascular disease ; 1.9. Chronic hepatitis. Hepatic cirrhosis; 1.10. Inflammatory bowel diseases ; 1.11. Chronic kidney disease ;

2. Drug or alcohol abuse as suspected by investigator;

3. History of persistent diarrhea of any cause;

4. Use of pre- or probiotics during the last 2 weeks before enrollment;

5. Allergy to any components of the TDS;

6. Technical difficulties to perform virtual study visits.

7. Inability to perform a blood test for antibodies after 6 months

8. Inability to swallow capsules, or choking / coughing while eating

Not applicable as not decided yet