The effects of Agaricus bisporus strain MES01706 on influenza vaccination responses: a double-blind, randomized, placebo-controlled intervention study in men and women aged 60 years or older.

To combat the gradual decline in immune function in older adults, nutritional interventions can be used to enhance this compromised immune response. Our previous in vitro and in vivo murine studies showed that the specific Agaricus bisporus strain MES01706 had clear immunomodulatory properties. Since effects in humans are unknown, we investigated the impact of daily supplementation with 5.0 g of Agaricus bisporus powder for 8 weeks on the vaccination response to an influenza vaccine in people aged 60 years or older during the 2023/2024 influenza season. A double-blind, randomized, placebo-controlled parallel trial was performed. Participants consumed capsules containing Agaricus bisporus powder (5 g d-1; n = 42) or placebo (n = 43) for approximately 4 weeks prior to vaccination until 4 weeks post-vaccination. Differences between groups in antibody titres, serum metabolic risk markers, and haematological and immunological parameters were statistically evaluated using linear mixed models. Compliance was excellent, demonstrated by a significant increase in ergothioneine (group × time, p < 0.01) in the intervention group compared with control. Median IgM antibody titres increased by 73% more in the Agaricus bisporus group compared to control (p = 0.09). IgG concentrations were not significantly different between the control and Agaricus bisporus group (p = 0.65). Moreover, no between-group differences were observed in changes in total or differential leukocytes counts, other metabolic parameters, quality of life, or influenza-like illness during the influenza season 2023/2024. Daily consumption of 5.0 grams Agaricus bisporus powder for 8 weeks did not significantly affect vaccination responses following the annual influenza vaccination in elderly men and women aged 60 years or older.