Antibiotics May Reduce Efficacy of Flu Vaccines by Disrupting Gut Microbiome, Study Shows

New research out of Stanford University suggests that antibiotics can reduce the efficacy of flu vaccines due to their effects on microbes living in the gut.

The word “bacteria” connotes something bad to most people. But as scientists have shown, humans need a fine balance of these microorganisms in their gastrointestinal tract to support good health.

Flu Shot

Flu Shot

It is also known that antibiotics that are often taken to deal with harmful bacteria reduce microscopic organisms in the gut. Now, researchers are saying that this is capable of rendering vaccination against seasonal influenza virus less helpful.

It was reported in new study published in the journal Cell that oral antibiotics lowered immune responses to vaccine for the H1N1 influenza virus.

“To our knowledge, this is the first demonstration of the effects of broad-spectrum antibiotics on the immune response in human – in this case, our response to vaccination – directly induced through disturbance of our gut bacteria,” said Bali Pulendran, a senior study author.

The new research was funded by the National Institute of Allergy and Infectious Diseases (NIAID),one of the institutes that make up the National Institutes of Health (NIH).

Altering immune response

Stanford researchers had shown in a 2011 study that disrupted gut microbiome in mice resulted in poor immune responses. The current study investigated similar effects in humans.

Scientists in the current study evaluated two groups comprising 33 healthy adults in total. They examined the first group made up of 22 subjects during the 2014-15 influenza season. The second was evaluated during the 2015-16 flu season.

It was found that participants from the first cohort saw 10,000 fold reduction in the diversity of their gut bacteria. This was after receiving three broad-spectrum antibiotics for five days prior to getting the vaccine. The subjects had high immunity against the 2014-15 flu virus strains before having the drugs.

As for the 11 volunteers in the second group during the 2015-16 flu season, they already had low immunity to the prevailing flu virus strains before they were subjected to similar experiment as before.

Half of all the subjects received only normal flu vaccine.

In addition to radically reduced gut microbiome among those treated with antibiotics, analysis of stool and blood samples revealed that the drugs inhibited immune responses to a particular flu virus strain, an H1N1 A/California-specific virus.

This seems to suggest that individuals in the second cohort who showed notably lower antibody responses to the H1N1 virus after antibiotic treatment lacked prior exposure to the strain. As a result, they were not amply protected against the virus and were less protected than those who did not receive antibiotics.

Pro-inflammatory state link

It is natural for microbiomes to change – decline – in humans as a result of aging. This has a link to a pro-inflammatory state that is commonly seen in older individual. This state is also a typical sign of early stage of several diseases.

Researchers observed in the current study that disruption of gut microbiome by antibiotics encouraged a pro-inflammatory state via changes to immune systems. Reduction in gut bacteria diversity resulted in disturbance of a process by which bile acid metabolism is regulated, according to the researchers.

A condition similar to a pro-inflammatory state has been observed in elderly people after receiving flu vaccines.

The Stanford scientists suggested the need for further research to better understand why older persons tend to respond to flu vaccines differently. Such should also help explain why the elderly often have weaker immune systems on the whole.

 

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