Mushrooms, particularly species like Lentinula edodes (shiitake), Ganoderma lucidum (reishi), and Coriolus versicolor (turkey tail), have gained scientific interest for their immunomodulatory and antiviral properties. Polysaccharides, such as beta-glucans found in these mushrooms, have been shown in laboratory studies to enhance the activity of immune cells like macrophages, natural killer cells, and T-lymphocytes. Some in vitro and animal studies demonstrate that mushroom extracts can inhibit replication of influenza viruses and may reduce severity of symptoms in infected mice.

However, direct clinical evidence in humans for the efficacy of mushrooms in preventing or treating influenza is limited. Most available human studies focus on general immune enhancement rather than specific antiviral activity against influenza. A few small clinical trials suggest that mushroom-derived supplements may reduce the duration or severity of upper respiratory tract infections, but these findings are not influenza-specific and often lack rigorous design or sufficient sample size.

In summary, there is some scientific rationale and preclinical evidence supporting the use of certain mushrooms for immune support and potential antiviral effects, including against influenza. However, robust clinical evidence in humans is lacking, and mushrooms should not be considered a primary or stand-alone treatment for influenza.