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As Hong Kong enters the winter influenza season, Professor Francis KL Chan, Choh-Ming Li Professor of Medicine and Therapeutics; and Director of the Centre for Gut Microbiota Research at The Chinese University of Hong Kong (CUHK)’s Faculty of Medicine (CU Medicine), said: “In addition to vaccination, the public can strengthen their immunity through other means. Studies have shown that short-chain fatty acids (SCFAs) produced by probiotic bacteria in the gut can boost immunity against influenza and other viral infections.”

High-fibre diet and exercise can help develop a healthy gut microbiome. Probiotic bacteria in the gut can produce SCFAs, which was shown to reduce viral loads, enhance vaccine efficacy and reduce serious complications following viral infection.

A recent review by CU Medicine published in the Trends in Microbiology, a journal of Cell Press, summarises the importance of SCFAs.  The review highlights that SCFAs produced by probiotic bacteria in the gut can help combat different viral infections, including influenza, COVID-19, and other upper respiratory tract viral infections. Professor Tun Hein Min, Associate Professor of the Jockey Club School of Public Health and Primary Care at CU Medicine, who led the study, said: “SCFAs are beneficial metabolites of the gut microbiota with immune-modulating properties. Produced by gut microbes through the fermentation of dietary fibre, SCFAs enhance the ability of respiratory tract cells to resist viruses, reduce viral loads, enhance the efficacy of vaccines, and minimise serious complications. Studies also showed that influenza patients are deficient in SCFA-producing gut bacteria. In other words, gut microbiota plays an important role in strengthening the immune system against influenza.”

Natural SCFAs are different from synthetic SCFAs

Professor Francis KL Chan added: “The evidence for SCFAs against flu is mainly from gut microbiota research. The efficacy of synthetic SCFAs has yet to be elucidated. Two essential elements to produce natural SCFAs are: high-fibre diet and a healthy gut microbiota.”

CUHK’s synbiotic formula can increase SCFA-producing gut bacteria

A large-scale, double-blind, randomised controlled trial published in The Lancet Infectious Diseases last year evaluated the effect of SIM01, a synbiotic formula developed by CUHK, on improving gut microbiota. Co-first author of the study, Dr Raphaela Iris Lau, Honorary Postdoctoral Fellow of the Department of Medicine and Therapeutics at CU Medicine, said: “According to our metagenomic analyses, treatment with SIM01 led to a significant increase in the abundance of SCFA-producing gut bacteria in recovered COVID-19 patients. Remarkably, many of the increased probiotic bacteria are depleted in the gut of influenza patients.”

This study was supported by the InnoHK Programme of the Hong Kong Special Administrative Region Government and the Health Bureau’s Health and Medical Research Fund (HMRF).