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Antibiotics interfere with influenza vaccine



One study shows that a decrease in the number of intestinal bacteria following antibiotic treatment compromises the immune response to influenza vaccine.

A virus with a thousand faces

Unlike vaccines developed against various viruses (such as polio, measles and HPV) that protect against these lifelong infections, influenza requires the production of a new vaccine and a new immunization for each season of influenza activity. This phenomenon is due to the property of the influenza virus to constantly modify its structure to create new ways that escape the immune system. Health authorities should therefore be constantly on the alert to identify the influenza strain or strains most likely to infect the population to achieve timely production of the corresponding vaccine. These predictions are generally quite accurate and annual vaccines can activate the immune response to circulating strains and reduce the risk of virus contraction.

But even when annual vaccines match the active strains of the virus, their effectiveness often falls short of expectations. For example, one study showed that inactivated trivalent vaccines have an average efficacy of 60%, while the vaccine developed in 2009 to combat dangerous H1N1 provided only 70% protection. (1). It appears that other factors, regardless of vaccine specificity, play a role in the immune response against influenza.

The Influence Of The Microbiome

According to a recent study, one of these factors could be the gut microbiome, ie the hundreds of billions of bacteria present in our digestive system. (2). It has been known for some years that these bacteria greatly influence the activity of the immune system and that disturbances in microbiome composition can promote the development of various immune disorders, such as allergies and autoimmune diseases. But it seems that this immunological action is much broader than we thought and would also participate in the response to vaccines: for example, a team of American researchers recently showed that when rats are kept from birth in a totally sterile environment (and therefore devoid of intestinal bacteria), they generate far fewer antibodies after vaccination than animals that have a normal microbiome.

To determine if a similar phenomenon is found in humans, the same research team recruited 22 adults aged 18 to 45 and divided them into two groups – 11 people who were simply immunized with the trivalent influenza vaccine (control group), while the remaining 11 were treated with antibiotic therapy with a cocktail of antibiotics (neomycin, vancomycin and metronidazole) to eliminate a wide range of intestinal bacteria prior to vaccination, producing a reduced microbiome.

Stool analysis of antibiotic patients obviously showed a very strong response to antibiotics, with a decrease of about 10,000 times the bacterial population. The results were spectacular: antibiotic treatment completely abolished the production of the major subtype of antibodies responsible for neutralizing the virus. This is a very interesting result that emphasizes once again the important link between the microbiome and the immune system.

In another experiment with people who already had antibodies against the influenza vaccine strains, antibiotic treatment had no impact on the immune response. Both groups had similar levels of influenza antibodies 30 days after vaccination, suggesting that previous exposure to viral strains of the vaccine may reactivate this immune memory, regardless of microbiome.

The disappearance of the intestinal microbiome therefore prevents the immune system from responding well to a new infectious agent, for example those present in the annual influenza vaccine. Further studies need to be done to confirm this association, but these results strongly suggest that people on antibiotic therapy should wait to complete their treatment and regenerate their intestinal flora before being vaccinated against influenza.

On the other hand, the study also shows that our immunity remains very resistant, because even in the complete absence of intestinal bacteria, it is still effective if it has been in contact with the virus in the past. It is therefore important to be vaccinated each year against the flu to expose our immune system to as many strains as possible and to be able to fight effectively when the time comes, even if our microbiome's health is not optimal. at the time of exposure to the virus.


(1) Osterholm MT et al. Effectiveness and efficacy of influenza vaccines: a systematic review and meta-analysis. Lancet Infect Dis. 2012; 12: 36-44.

(2) Hagan T et al. Disruption of the gut microbiome caused by antibiotics alters immunity to vaccines in humans. cell 2019; 178: 1313-1328.


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