This is a randomised, open-label and controlled clinical trial aimed to investigate the adjuvant treatment benefits of probiotic Streptococcus salivarius K12 in hospitalised mild-to-moderate patients with COVID-19 disease.

Boosting the immunity and maintaining a healthy and balanced microflora at oropharyngeal environment of people through probiotics supplementation has been proposed as a possible strategy to protect human host from respiratory tract infections. A slow-dissolved oropharyngeal probiotic formula containing S. salivarius K12 has been clinically demonstrated to improve the upper respiratory tract microbiota protecting the host from pathogenic bacteria, fungi, and viruses, thereby reducing the incidence of viral respiratory tract infections and bacterial co-infections. S. salivarius K12 has been proposed as a promising agent for prophylactic or probiotic treatments to protect individuals during the outbreak of seasonal or emerging respiratory infection diseases.

S. salivarius K12 strain, commonly known as BLIS K12, is a highly safe, and extensively-studied probiotic that resides in the oral cavity. BLIS K12 has a solid scienctific rationale for helping to prevent streptococcal pharyngitis and/or tonsillitis, ear infections (otitis media) and to help treat halitosis. It is a specific strain of Streptococcus Salivarius, which secretes powerful anti-microbial molecule called Bacteriocin-Like-Inhibitory Substances (BLIS). The ingredient is believed to support healthy bacteria in the mouth for long-term fresh breath and immune support.

It is proposed that the oral administration of the strain K12 to hospitalized COVID-19 patients (not already in ICU) receiving supplementary oxygen (not invasive oxygen theraphy) to exploit the "ventilation" and helping S. salivarius (K12) to move from the mouth (it is an oral colonizer) to the lungs, colonizing them. The idea is that the lung presence of K12 could strategically reduce the lung and immune capability to release pro-inflammatory cytokines, thus preventing excessive lung inflammation, and the need to proceed to ICU and death.

Inclusion Criteria:

• Age ≥ 18 years (both sexes)
• Hospitalized confirmed (RT-PCR) COVID-19 patients (not already in ICU) admitted for treatment of COVID-19 and not receiving mechanical ventilatory support
• Patients who have signed informed consent

Exclusion Criteria:

• Patients with proven hypersensitivity or allergic reaction to the tested formula
• Patients who decline to participate in the study