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Does Your Gut Health Play A Role In How Well The Flu Vaccine Works For You?

Laura Kunces, PhD, RD

We know the flu vaccine works differently across different demographics. And each year, the news reports how the elderly, children, and those with a compromised immune system are at the biggest risk for the serious, life-threatening effects. So research to identify the factors that can support our best possible health and most effective response to the flu vaccine is welcome.

As with most health research, the earliest findings of the connection between gut health and immune function were in animal models.1 Fortunately for us, there is now human clinical research to back up some of the animal studies. For example, we can now say we’ve established a strong link between gut health and the immune system – more specifically regarding the effectiveness of flu vaccines in human adults.

Emerging Flu Vaccine Research

Recently published research in Cell examined adults who had not had the flu shot or came down with the flu in the past three years.2 Study participants received a flu shot, or a 5-day course of broad-spectrum oral antibiotics then a flu shot. Researchers followed these two groups for about a year – taking blood and stool samples throughout the year. And what they found was remarkable! 

Those who had the antibiotics before receiving a flu vaccine produced fewer antibodies once given the shot, and therefore, produced a weaker response to the vaccination compared to those who did not take antibiotics. Similarly, those treated with the antibiotics also presented with gut dysbiosis, an increased inflammatory response, and a significant decrease in bile acid secretion in the blood.

What is it about antibiotics that influence the vaccine response? Antibiotics are not necessarily specific to certain bacteria. And in this case, the course of a broad-spectrum antibiotic kills any and all bacteria within its path – the good, the bad, and the plenty. This change in the gut is known as dysbiosis or an imbalance of pathogenic to beneficial bacteria. And it's gut dysbiosis that then further influences a variety of immune functions, creating cascading effects throughout the body.

It’s not that antibiotics are bad. In fact, they are good when used judiciously for bacterial infections. If you do take antibiotics, however, you should consider how you can maintain or restore the good, essential bacteria in your system.

Previous Flu Vaccine Research

Historically, research with the flu vaccine has proven our immune system is complex, dynamic, and systemically connected to our whole body. Almost a decade ago, researchers made a breakthrough in understanding the mechanisms behind the flu vaccine. Scientists found those who received the vaccine presented with increased activity of the gene that encodes (or specifies) a receptor in the innate immune system. This gene is the one that recognizes the bacterial protein flagellin, the core part of flagella that many microbes use to move. What does this all mean exactly? This research started to paint the picture of how genes and the microbiome (which is in integral part of the innate immune system) talk to each other. The flu vaccine activates a response that “speaks” to both through the bacteria present in your system, which ultimately can influence how you respond to the vaccine. 

Another group of scientists followed up this initial work by studying the flu vaccine and specific cellular receptors for bacterial flagella in mice models.3 They bred a group of mice to have the special cellular receptors for a type of the flu vaccine and a group without the receptors. In this study, they purposefully depleted their microbiomes with antibiotics and then gave the flu vaccine. While they found the receptors to play an important role, it also turns out all of the mice had a reduced response to the vaccine, which means the gut does indeed impact the response to the vaccine in these rodents. 

And once this model was established in animals, the scientists were able to show it in humans too. These findings are shaping the public health measures we take this flu season and should make you think about your gut health status before getting your yearly influenza shot. 

Gut microbiome diversity is a key metric for assessing your gut health. Check your status of gut bacteria and diversity level with Gutbio™ from Onegevity, which measures your number and compares you to others. We also provide a full download of every microorganism found in your sample to keep you informed of the good, bad, and plenty of bacteria.

1.     Pulendran B, Maddur MS. Innate immune sensing and response to influenza. Curr Top Microbiol Immunol. 2015;386:23-71.

2.     Hagan T, Cortese M, Rouphael N, et al. Antibiotics-Driven Gut Microbiome Perturbation Alters Immunity to Vaccines in Humans. Cell. 2019;178(6):1313-1328.e13.

3.     Oh JZ, Ravindran R, Chassaing B, et al. TLR5-mediated sensing of gut microbiota is necessary for antibody responses to seasonal influenza vaccination. Immunity. 2014;41(3):478-492.