Flu Vaccine Effectiveness Influenced By Oral Antibiotics

A new research paper found that oral antibiotics, which can kill gut microorganisms, can alter the human immune response to seasonal influenza vaccination.

This paper’s finding is important since antibiotics and vaccines represent widely used medical interventions and have important implications for clinical practice and public health policy.

The work was published on September 5, 2019, led by scientists at Stanford University and funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.

Alan Embry, Ph.D., Chief of the Respiratory Diseases Branch in NIAID’s Division of Microbiology and Infectious Diseases, wrote the following press release, excerpts are integrated below.

All study participants received a seasonal influenza vaccine. Half the participants in each group also received a 5-day course of a broad-spectrum antibiotic regimen, consisting of neomycin, vancomycin, and metronidazole, by mouth before receiving the flu vaccine. 

By analyzing stool and blood serum samples taken at various times up to 1-year after vaccination, the researchers tracked the participants’ immune response to the influenza vaccines, as well as the diversity and abundance of the organisms in their gut microbiomes.

As expected, most participants who received antibiotics experienced reduced levels of gut bacteria. 

In addition, among the 2015-2016 participants who had little prior immunity to the seasonal influenza virus vaccine strains, a course of antibiotics hindered their immune responses to one of the 3 influenza virus strains in the vaccine, an H1N1 A/California-specific virus. 

This likely indicates that should they be exposed to this H1N1 virus after vaccination, these participants would be less protected against infection with that strain than people who had not received antibiotics, according to the authors.

The researchers also found that people who took antibiotics experienced changes to their immune systems that promoted a pro-inflammatory state, similar to a condition seen in older adults who have received influenza vaccines. 

The investigators believe this pro-inflammatory state is related to the process by which the microbiome regulates the metabolism of bile acid—with fewer microorganisms, this process is disrupted. 

Human microbiomes change naturally as they age, and the researchers suggest that further research on these pathways could provide insights into why older adults respond differently to influenza vaccination and why they have weaker immune systems overall.

NIAID conducts and supports research—at NIH, throughout the United States, and worldwide—to study the causes of infectious and immune-mediated diseases and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets, and other NIAID-related materials are available on the NIAID website.

Published by Precision Vaccinations