The Flu and the Microbiome: One Reason Those Over 60 Are More At Risk

Back in 2017, I told you about research out of Georgia State University which looked at the effect of probiotics (specifically, Lactobacillus casei) on influenza infection, in an animal model.  The research demonstrated that the probiotic was effective at warding off severe influenza and this is not the only study to have demonstrated this.  Research done earlier had already shown that in mice, B. subtilis worked as well as Tamiflu.  h

New research has just been published in the eminent journal, The Lancet, this time on humans.[i]  Stool samples were collected from 397 participants in the Netherlands during the flu season of 2014-15.  The group contained  an equal number of men and women and all were aged 60 or older. Past research has shown that the influenza vaccine is markedly less effective in those over 60 (estimates range from 17% – 53%, but even at best, that’s only a little more than 50% effective!)…and of course, the older you are, the more at-risk you are of serious complications from the flu.  In comparison, the flu vaccine is estimated to be 70-90% effective for younger populations.  Thus, finding a means of protecting those over 60 becomes that much more important.  According to this article, those over 60 have a 90X higher rate of mortality from infections like influenza than do those who are younger.

The participants filled out questionnaires to determine whether or not they had any influenza-type illness (ILI) during the period of the study.  In the group, 213 had indeed experienced an ILI while 184 did not.  192 of those who had an ILI submitted fecal samples after they had recovered as well.

In those who had experienced a flu-like illness, the scientists found higher levels of Ruminococcus torques.  Prior research had already associated this species with intestinal barrier dysfunction as well as increased blood triglyceride levels:  “R. Torques was associated with pro-inflammatory profiles, both locally in faeces and systemically in blood.”  Higher levels of the pathogenic Escherichia/Shigella was also found. During the actual period of illness, microbiome profiles were altered.  For example, Bacteroidetes tended to be at much higher abundance in the ILI group than the non-sick controls, as were Proteobacteria, while there was a relative decrease in the abundance of Firmicutes.  Overall, there was a decrease in butyrate-producing bacteria which, as you know from many previous posts, can lead to compromised epithelial barrier health.

They conclude that changes in microbiota composition that occurs when sick in those over 60 leads to a generalized pro-inflammatory state that, “…could result in more severe disease outcomes and increased susceptibility to frequent bacterial or fungal superinfections in this population.”  (How much does this sound like what is happening with COVID?!)

They authors suggest that the abundance of certain bacteria or lack thereof may be used as biomarkers for ascertaining the susceptibility of older people to respiratory infections.   And of course, “…better understanding of host–microbe interactions in the gut–lung axis is key for the design of potential therapeutic strategies.” With the annual flu vaccine’s lack of established efficacy in this population, the importance of finding ways to prevent and treat the flu cannot be overstated.  In the meantime, I have my parents on a daily high-potency probiotic.


[i] Fuentes, S., den Hartog, G., Nanlohy, N.M., et al. (2021). Associations of faecal microbiota with influenza-like illness in participants aged 60 years of older: an observational study. The Lancet 2(1), E13-E23. Doi: 10.1016/S2666-7568(20)30034-9

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