This 2021 review subject was effects of the 100-year-old tuberculosis vaccine:
“Bacillus Calmette-Guerin (BCG) vaccine is one of the most widely used vaccines. It protects against many non-mycobacterial infections secondary to its nonspecific immune effects.
The mechanism for these effects includes modification of innate and adaptive immunity. BCG vaccine is known to not only boost immune responses to many vaccines when they are co-administered, but also decreases severity of these infections when used alone.
Alteration in innate immunity is through histone modifications and epigenetic reprogramming of monocytes to develop an inflammatory phenotype, a process called trained immunity. Memory T cells of adaptive immunity are also responsible for resistance against secondary infections after administration of BCG vaccine, a process called heterologous immunity.
The PI3K/AKT pathway, another pathway for mediating immunity, was upregulated. This was supported by recent studies demonstrating its involvement in induction of trained immunity by both BCG and β-glucan.
BCG vaccine can modify both innate and adaptive immunity, and provide immunity not only against Mycobacterium tuberculosis but also other pathogens. Heterologous immunity and trained immunity contribute to pathophysiologic mechanisms which explain how a vaccine protects against unrelated pathogens.”
https://www.amjmedsci.org/article/S0002-9629(21)00092-6/fulltext “Bacillus Calmette-Guerin Vaccine and Nonspecific Immunity”
As inferred by “induction of trained immunity by both BCG and β-glucan” many of these findings also apply to yeast cell wall β-glucan treatments. See Choosing your future with β-glucan for a representative study.