At the end of 2019, a new type of coronavirus was discovered in Wuhan, China, and spread rapidly, causing a pandemic of new coronary pneumonia around the world. In February 2020, the World Health Organization(WHO) named this disease is COVID-19. At present, no effective drug has been found to treatment for COVID-19, and only vaccine research and development are continuing. Now only a few vaccines have been reported in the third phase of human trials and have been emergency use authorized by the World Health Organization to implement preventive vaccines in countries around the world. So far, supportive therapy is still the main method of treatment, mainly to reduce the occurrence of severe illness. Although it is not clear whether probiotics can prevent or improve COVID-19-related symptoms, a study in Zhejiang, China shows that COVID-19 patients suffer from intestinal microbial disorders, especially in the decrease in the number of lactobacilli and bifidobacteria. In the same study, probiotics were used as adjuvant(assistant) therapy to adjust the balance of the intestinal microbiota and effectively reduce the risk of secondary infections in these patients, indicating that probiotics may have the opportunity to play a secondary role in the treatment of COVID-19.
 
In fact, the gut-lung axis theory can reflect the possible effects of probiotics in the COVID-19, because the immune response of many respiratory diseases is mediated by the distal intestine. There have been many studies on the intervention of intestinal probiotics to alleviate respiratory diseases. For example, Lactobacillus plantarum and Lactobacillus paracasei help to improve influenza infection.
 
Besides, in addition to the theoretical possible benefits of probiotics against pneumonia on the gut-lung axis, the anti-viral and anti-inflammatory ability of probiotics should also be one of the possible benefits of alleviating the symptoms of COVID-19. Studies have shown that certain lactic acid bacteria can directly stimulate plasma cell dendritic cells (pDC) via Toll-like receptor 9 (TLR 9), causing interferon production to control virus replication and spread. A new peptide-P18 produced by probiotics has been isolated and showed complete inhibition of influenza virus in vitro tests; its anti-viral effect on mice is equivalent to that of Tamiflu. In human clinical trials, a randomized, double-blind, placebo-controlled trial showed that taking probiotics during preterm infants can significantly reduce the incidence of viral respiratory infections.
 
It is currently understood that patients with COVID-19 have an increased inflammation index and are in an inflamed state. Reducing inflammation and the immune storm is another important benefit of probiotics. Many studies have shown that probiotics can reduce T cell auto-reactivity and pro-inflammatory cytokines (peroxidase activity, iNOS, COX-2, TNFα, IL-6) production, increase anti-inflammatory factors (such as IL-10 and nitric oxide). A clinical study on the effects of probiotics on respiratory diseases showed that ventilator use rate was significantly reduced in pneumonia patients who administrate probiotics. It can be speculated that probiotics can alleviate the severe proportion of pneumonia.
 
Based on some of the important benefits of probiotics for respiratory diseases, many countries have conducted some studies on probiotics to alleviate COVID-19 symptoms. For example, a research team in Belgium is exploring the potential of specific Lactobacillus strains in the nasopharynx and oropharynx by enhancing the barrier and anti-inflammatory effects to reduce the activity of the SARS-CoV-2 and reduce the risk of secondary bacterial infections from COVID-19; In the United States, a multicenter, randomized, double-blind, phase 2 trial was conducted using Lactobacillus rhamnosus GG and placebo to observe its ability to reduce the incidence of COVID-19 and improve its symptoms.
 
In general, probiotics that regulate the intestinal microbiota may have the opportunity to relieve the symptoms and complications of COVID-19, but the utility of probiotics as an additional therapy may require further research in bed trials to determine their effectiveness and safety.
 
 
References:
 
A. Akour. (2020) Probiotics and COVID-19: is there any link? Letters in Applied Microbiology 71, 229--234
Xu, K., Cai, H., Shen, Y., Ni, Q., Chen, Y., Hu, S., Li, J., Wang, H. et al. (2020) Management of corona virus disease-19 (COVID-19): the Zhejiang experience. Zhejiang Da XueXueBao Yi Xue Ban 49, 147–157.
Kanauchi, O., Andoh, A., Abubakar, S. and Yamamoto, N.(2018) Probiotics and paraprobiotics in viral infection: clinical application and effects on the innate and acquired immune systems. Curr Pharm Des 24, 710–717.
Starosila, D., Rybalko, S., Varbanetz, L., Ivanskaya, N. andSorokulova, I. (2017) Anti-influenza activity of a Bacillussubtilis probiotic strain. Antimicrob Agents Chemother 61,https://doi.org/10.1128/AAC.00539-17
Zeng, J., Wang, C.T., Zhang, F.S., Qi, F., Wang, S.F., Ma, S., Wu, T.J., Tian, H. et al. (2016) Effect of probiotics on the incidence of ventilator-associated pneumonia in critically ill patients: a randomized controlled multicenter trial.Intensive Care Med 42, 1018–1028.