To date, various manifestations of allergic reactions and diseases are registered in 15-35% of the population according to the World Health Organization, and in recent years there has been a constant tendency to increase [1]. The first sign of allergic pathology in children, as a rule, is a food allergy, which is mainly manifested by atopic dermatitis. According to official statistics, the rate of atopic dermatitis in Ukraine is known to range from 3 to 10 per 1000 children [2]. However, the results obtained in some regions of our country according to studies under the standardized international program ISAAC (International Study of Asthma and Allergies in Childhood), exceed the above figures by 5-10 times [3]. This situation can be explained by the presence of terminological differences in the interpretation of atopic dermatitis in children, different methodological approaches to statistical research, clinical and age-related polymorphism of the disease. The development of atopic march can begin with a food allergy, so all efforts of physicians should be directed to prevent the transformation of skin forms into respiratory ones and provide the patient and his/her parents with a full quality of life [4,5]. The “School of Atopy” operates under the auspices of the MNPE “Lviv City Children’s Clinical Hospital” and the Lviv City Children’s Allergological Center, where a model of a multidisciplinary approach to the management of patients with food allergies according to European standards was reproduced. Every patient treated for food allergies goes from diagnosis to treatment. Of course, great emphasis is placed on preventing and predicting the development of atopic march in children and improving the quality of life of patients and their parents. 

Acute respiratory tract infections (ARTI) place an enormous impact on patients and primary healthcare system due to their extraordinary incidence. In 2019, the world prevalence of ARTI reached 17.2 billion and accounted for 43.8% of all causes of the global disease burden [1]. Respiratory infections are the most common reason for seeking medical attention, with personal recurrence rates ranging from 2 to 6 times per year [2]. Although usually mild and self-limiting, ARTIs significantly affect work productivity and quality of life [3].

Emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing corona virus disease 2019 (COVID-19) brought a new challenge, being both common and severe, affecting upper and lower airways with considerable constitutional symptoms. As with other respiratory infections, the management of outpatients with mild COVID-19 without risk of progressing to severe disease, remains supportive and include close observation for early recognition of the life-threatening symptoms, reduction the risk of further SARS-CoV-2 transmission, advising on when to seek an in-person evaluation [4]. Absence of the effective specific measures in most COVID-19 cases serves a rationale for exploration of a new complementary approaches, one of which may be the use of probiotics.

Indirect evidence shows that patients with COVID-19 and diarrhea have more severe disease, increased concentration of inflammatory cytokines, markers of tissue damage, suggesting the intestinal cells can serve an additional entry and reservoir for SARS-CoV-2 [5, 6]. As with type II alveolar cells, intestinal and colonic enterocytes express angiotensin I converting enzyme 2 (ACE2), a receptor though which SARS-CoV-2 inoculates the body [7]. Bifidobacteria and lactobacilli adhering to enterocytes can hypothetically interfere with infection process and disease manifestation [8,9,10]. Interestingly that bacteria may potentially downregulate amide and peptide metabolism in the gut including angiotensin-converting enzyme 2 (ACE2) [11, 12]. It may explain the reason that cell cultures exposed to probiotics yielded lesser amount of transmissible gastroenteritis coronaviruses [13]. Additionally, the beneficial effects of probiotics in respiratory infections can be realized via several non-specific mechanisms discussed within the gut-lung axis paradigm [14], including enhancement of innate antiviral immune defense [15]. A recent systematic review of 23 randomized clinical trials involving a total of 6950 participants with ARTI, demonstrated fewer cases, shorter case duration, and reduced antibiotic prescription rates in patients taking probiotics [16].

The objective of this study was to assess the role of short-term ingestion of probiotics in mild symptomatic COVID-19, post-disease symptoms, and humoral immune response to SARS-CoV-2 in outpatients.