1 Probiotics and COVID-19 Domina Petric, MD ABSTRACT SARS-CoV-2 is an enveloped virus with a single-stranded positive sense RNA genome. Vaccine efficacy can be limited by mutations in RNA viruses and search for alternative/additional effective therapies must continue. Probiotics are generally considered safe. There is a good scientific evidence to support the ability of probiotics to boost human immunity. It is rationale to support the use of probiotics in prevention and treatment of viral infections, including COVID-19. In addition to that, the use of probiotics in COVID-19 can serve as protective factor against cytokine storm and consequential autoimmunity. INTRODUCTION SARS-CoV-2 is an enveloped virus with a single-stranded positive sense RNA genome 1 . Vaccine efficacy can be limited by mutations in RNA viruses, as observed for the influenza virus as a representative pathogenic virus 2, 3 . The gastrointestinal microbiota has the ability to interact with human cells, including specific immune cells. These interactions produce different health benefits in the host including regulating gastrointestinal motility; activating and destroying toxins, genotoxins, and mutagens; transforming bile acid and steroids; producing vitamins; absorbing minerals; metabolizing xenobiotic substances; influencing intestinal permeability and barrier functions; and modulating mucosal and systemic immunity; as well as beneficial effects on the skin and upper respiratory tract 4, 5 . PROBIOTICS AND COVID-19 Probiotics consist of single or mixed cultures of live microorganisms that can beneficially affect the host by maintaining the intestinal or lung microbiota that play a major role in human health. At present, good scientific evidence exists to support the ability of probiotics to boost human immunity, thereby preventing colonization by pathogens and reducing the incidence and severity of infections. Data from clinical studies of the use of probiotic supplementation to prevent or treat respiratory tract infections (reviewed by