The first randomized, controlled clinical trial testing a probiotic for the treatment of COVID-19 in mild to moderate patients.

Scientific Evidence

4x blinded, single-center, randomized, placebo-controlled study. 300 patients with mild to moderate COVID-19 symptoms 

Patients were randomized to take orally once a day probiotic AB21 or placebo, for 30 days

Remission of symptoms was achieved in 53.1% of patients in the probiotic group, compared to 28.1% of patients in the placebo group (p<0.0001)

A pioneering and innovative publication that contributes to microbiome science and increases the evidence behind the gut-lung axis

Parallel arms

Mild to moderate COVID-19

18 to 60 year-old (median age of 37)

Criteria -

  1. At least 1 COVID-19 symptom (cough, headache, fever, muscular pain, shortness of breath)

  2. Positive RT-qPCR

  3. Symptom onset less than 7 days before recruitment

  4. No need of oxygen therapy

Almost half of subjects with known
metabolic risk factors (diabetes, obesity)




randomized, placebo-controlled clinical trial

4x blinded

(patient, caregiver, investigator and outcomes assessors)

300 patients,

one dose daily


Study Start

Study End

and random

Placebo group

1 capsule a day, 20 minutes before breakfast

AB21 group



AB21 shortened median symptoms duration by 5 days


-5 days

The probiotic group had a median symptoms duration of 13 days, while in the placebo group it was 18 days.