Taking probiotic or prebiotic supplements before receiving specific influenza vaccines can improve the protective effects of the vaccines in adults

Lei. Effect of probiotics and prebiotics on immune response to influenza vaccination in adults: A systematic review and meta-analysis of randomized controlled trials Nutrients. 2017;9: pii: E1175.

Review question

How does consuming probiotic or prebiotic supplements effect how the immune system responds to influenza vaccination in adults?

Background

Influenza is a respiratory infection caused by different viruses. Globally, three to five million cases of serious illness and approximately 250,000-500,000 deaths occur as a result of seasonal influenza each year. Probiotics are live bacteria and prebiotics are substances that encourage the growth and digestion of intestinal bacteria; both have been shown to protect against influenza in clinical trials, and positively affect the functioning of the immune system. The impact of probiotics and prebiotics on immune system responses that are triggered by the influenza vaccine has also been assessed by randomized controlled trials (RCT), but to date their effect on influenza-related outcomes among adults has not been evaluated in a systematic review.

How the review was done

This is a systematic review of 20 RCTs published between 2002 and 2017, including a total of 1979 participants. Nine of the RCTs were included in a meta-analysis.

• Participants were adults classified as either: healthy young to middle-aged adults, healthy older adults, or frail or hospitalized older adults. The average age was 58.1 years old.   
• Study participants either took probiotic supplements, supplements containing prebiotics mixed with different combinations of other substances such as vitamins, minerals, oils, fermented milk etc., or supplements that combined both probiotics and prebiotics for 2-28 weeks. All participants received one of the following influenza vaccines alone or in combination with a pneumonia vaccine: a vaccine that contained live but weakened influenza viruses or a vaccine that contained inactive influenza viruses and protected against three different strains of influenza. The strains of influenza included in the vaccines were H1N1, H3N2, and influenza B.
• Researchers measured seroconversion and seroprotection rates. Seroconversion rate is the percentage of participants who experienced a four-fold increase or more in the amount of antibodies in their blood following influenza vaccination. Seroprotection rate is the percentage of participants that had an amount of antibodies in their blood that is associated with the ability to prevent influenza infection.
• Results were compared to people in control groups who received a placebo. 

What the researchers found

Overall, the consumption of probiotics or prebiotic supplements before influenza vaccination increased the effectiveness of influenza vaccines in adults, compared to those receiving placebo. Different effects were seen for seroconversion and seroprotection rates based on the influenza strain, supplements consumed, participants’ health status, and duration of supplement consumption:

• Probiotic use increased the seroconversion rate for the H3N2 and B strains but not the H1N1 strain, while prebiotics had no effect on seroconversion for any strain.
• Probiotic use increased the seroprotection rate for the H3N2 strain but not the H1N1 or B strains, while prebiotics increased seroprotection for the H1N1 and H3N2 strain, but not the B strain.
• Prebiotics or probiotics appear particularly effective in healthy older adults and when taken for longer durations.

Most of the included studies had a low risk of bias. However, larger studies with better reporting of data are needed to confirm the findings, and identify the most effective duration and dose of supplementation.

Conclusion

The consumption of probiotics or prebiotics before influenza vaccination can increase the effectiveness of influenza vaccines in adults, and specifically for the H1N1, H3N2, and B strains. Healthy older adults may benefit most from supplementation, as well as those taking supplementation for a longer amount of time.