Gut bacterium may boost COVID-19 vaccine efficacy

Bifidobacterium adolescentis, a unique gut bacterium, is correlated with the efficacy of the inactivated and mRNA coronavirus disease 2019 (COVID-19) vaccines available in Hong Kong, a collaborative study between the Chinese University of Hong Kong (CUHK) and the University of Hong Kong (HKU) has shown.

The researchers recruited 138 citizens 18–67 years of age (mean age, 47 years; female, 67.9 percent) between April and August 2021. The participants were asked to provide blood and faecal samples before vaccination and 1 month after receiving the second dose of the inactivated CZ02 vaccine (n=37) or mRNA-based BNT162b2 vaccine (n=101). The relationship between antibody level and gut microbiota was evaluated using metagenomics sequencing.

Results showed that individuals who lacked B. adolescentis had a suboptimal antibody response to CZ02 compared with those who had a high abundance of B. adolescentis (p=0.039). A close correlation between the level of B. adolescentis and a person's antibody response to CZ02 was found. Among BNT162b2 recipients, those who showed the lowest antibody response (ie, lower quartile) also lacked two bacteria, including B. adolescentis.

“CZ02 is known for fewer side effects but is also less protective in terms of antibody response. Over half of the individuals [57 percent] who received CZ02 had inadequate neutralizing antibody levels,” said Professor Siew-Chien Ng of the Centre for Gut Microbiota Research, CUHK. “Our results imply that B. adolescentis may offer a potential therapeutic option to enhance the efficacy of both CZ02 and BNT162b2.”

“This is the first human study to provide evidence that gut microbiota modulates vaccine response, with two possible mechanisms,” said Dr Hein Tun of the School of Public Health, HKU. “Firstly, some components of gut bacteria, such as flagellin, serve as natural adjuvant to enhance antibody production. Secondly, gut microbiota produces metabolites such as short chain fatty acids that can enhance immune cell metabolism to support energy demands for antibody production.”

“This new discovery is consistent with our earlier clinical finding that a microbiota-based regimen, which contained B. adolescentis, led to enhanced antibody response among COVID-19 patients,” added Professor Francis Chan of the Centre for Gut Microbiota Research, CUHK.

Although B. adolescentis is demonstrated to be the key to modulating the efficacy of COVID-19 vaccines, 85 percent of the Hong Kong population either had very low level (34.1 percent) or did not have (50.4 percent) B. adolescentis in the gut.

“B. adolescentis is present in a person’s gut since birth, but its quantity rapidly decreases with age, stress, modern diet, and the use of antibiotics. Diet alone is inadequate to restore adequate levels of this bacterium in the gut,” said Ng.

“Many health supplements in the market contain bifidobacterium. However, very few of them specifically contains B. adolescentis. As this bacterium is very sensitive to environmental conditions, including oxygen, high temperature and humidity, special technology is required to preserve this bacterium for dietary supplementation,” explained Ng.