Introduction:
COVID-19 pandemic caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is increasingly affecting people worldwide. To date, there is no established prevention or treatment protocol for this new virus. Millions of people suffer from COVID 19 despite social distancing, hand hygiene, healthy diet, and life style and mask wearing. Although several brands of vaccines with different efficacy have been approved and vaccination started in some countries, , It won’t be available for all people especially indeveloping countries. It necessary to work on other effective preventive measures that are able to reduce the risk of SARS-Cov2 infection with negligible side effects. This can be used in community or at least in high risk groups such as health care providers [1].
One of the potential strategies can be probiotics with the ability to boost human immunity[2]. Recent studies revealed that gastrointestinal microbiota have an important role in balance and proper function of immune system [3, 4]. Probiotics have been used in different immune-mediated and inflammatory disorders [5-9]. Probiotics can improve immune system functions via different mechanisms. One of them is increasing IgA secreting plasma cell numbers in lamina propria of intestine, lung and mammary gland [10-12]. This immunoglobulin has a major role in mucosal immune system[13]. Besides humoral immunity, healthy commensal microbiota of intestine can increase CD4+ T cells and regulatory T cells of GI lamina propria.
Bradley et al. in 2019 showed that the intestinal microbiota influence the IFN-α/β receptor surface expression in respiratory epithelial cells, which in case of a respiratory virus infection are able to respond more efficiently to type I IFNs stimulation with enhanced interferon-stimulated genes (ISGs) levels and impedes early virus replication[14]. A high-fiber diet (Prebiotic) increased the production of acetate by the intestinal microbiota and modulated the activity of respiratory IFN-β and increased the expression of ISGs in the lung[15]. Furthermore, gut microbial components and metabolites (postbiotic) including short-chain fatty acids (SCFA), are involved in gut-lung communication.
To date several studies revealed that probiotics could reduce upper respiratory infections incidence, duration and disease severity[16, 17]. A Cochrane review concluded that probiotics were better than placebo in reducing the number of episodes of acute upper respiratory infection (URTI), the mean duration of an episode of acute URTI, antibiotic use and school absence[18]. A recent systematic review and meta-analysis in 2020 concluded that synbiotic interventions reduced the incidence rate of respiratory tract infections (RTIs) by 16% and the proportion of participants experiencing RTIs by 16%[19]. Sly et al. showed that when using Immunostimulant OM-85 in infants, the cumulative frequency of severe lower respiratory tract infection and the number of days with symptoms were significantly lower compared to placebo, suggesting a reduction in the overall inflammatory burden in the lower airways [20].
The immunomodulatory effects of probiotics are strain-dependent[21]. Many trials using Lactobacillus Rhamnosus GG, Lactobacillus Plantarum, Lactobacillus Casei and Paracasei and some strains of Bifidobacterium could have preventive effects against respiratory infections. These scientific evidences have opened the possibility of exploring particular strains of beneficial probiotic with immunomodulatory capacities (immunobiotics) in order to increase antiviral defenses in the respiratory tract, especially the combination of probiotic and prebiotics which is called synbiotic[14, 19].
David Baud and colleagues provided a list of probiotic products with documentation in human studies that may have relevance to reducing the burden of the coronavirus pandemic [1].We recently showed that synbiotic Lactocare® intervention can reduce the episodes of viral respiratory infections in asthmatic children[22]. Interestingly, some probiotic strains in Synbiotic Lactocare® are similar to Strains suggested by David Baud. After COVID-19 pandemic, we proposed that Synbiotic Lactocare® may also reduce SARS-Cov2 infection in high risk medical staff working in COVID-19 hospital wards.