Researchers find gut microbes can affect COVID vaccine response

Researchers from Karolinska Institutet in Sweden have discovered that the gut microbiome can influence how well people respond to mRNA COVID vaccines. The study, published in the journal npj Biofilms and Microbiomes, suggests that certain bacteria in the gut can enhance the immune response to the vaccine, whereas other bacteria may weaken it.

The gut microbiome is the collection of microorganisms that live in our digestive tract. It plays an important role in many aspects of our health, such as digestion, metabolism, and immunity. The researchers wanted to find out if the gut microbiome also affects the response to mRNA COVID vaccines. To do this, they collected stool samples from 68 people living with HIV and 75 healthy individuals before their first mRNA COVID vaccine dose.

The researchers analyzed the microbiome composition using a technique called 16S rRNA sequencing, which identifies the types and relative abundance of bacteria in the samples. They also measured the levels of antibodies and immune cells that were produced after the vaccination.

"We correlated the microbial composition with immune responses and patient characteristics. This comprehensive analysis included age, gender, body mass index and clinical factors for people living with HIV, aiming to understand the complex relationship between gut microbes and vaccine efficacy," says principal investigator Piotr Nowak, senior physician and associate professor at Karolinska Institutet's Department of Medicine, Huddinge.

The results showed that the initial makeup of the gut microbiome could predict the immune response to the vaccine in both groups. They found that a less diverse gut microbiome was associated with a stronger vaccine response, marked by higher levels of spike protein antibodies and spike specific CD4 T-cells. These are key components of the immune system that help to neutralize the virus and prevent severe infection.

The researchers also identified specific bacteria that were linked with better or worse vaccine responses. For example, they found that Lactobacillus, Bacteroides, and Lachnospira were associated with higher antibody and immune cell levels, while Cloacibacillus was associated with lower antibody levels. They also found that Bifidobacterium and Faecalibacterium were microbial markers of individuals with higher antibody levels.

According to the researchers, the study highlights the significant role of the gut microbiome in the effectiveness of mRNA COVID vaccines. The findings could lead to developing microbiota-focused treatments to enhance vaccine responses, especially in groups that may have weaker responses, such as the elderly or immunocompromised individuals. The potential strategies could include changing the diet or taking probiotics to improve the gut microbiome and immunity, the researchers suggest.