It's recently been proven that a lot of our immunity stems from the gut and the bacteria within it. Vaccines, on the other hand, circumvent that system because it's injected directly into muscle tissue.
Gut bacteria essential for immune cell development - Medical News Today
Gut bacteria instrumental to development of innate immune cells
In this latest study, published in the journal Cell Host & Microbe, they describe how they discovered that beneficial gut bacteria played a key role in the development of innate immune cells - specifically macrophages, monocytes and neutrophils - special white blood cells that provide a first line of defense against invading pathogens.
These white blood cells do not only circulate in the blood, they are also stored in the spleen and in bone marrow. When the team compared counts of white blood cells in these areas in mice born without gut bacteria - known as "germ-free" mice - and healthy mice with a normal gut bacteria population, they found the germ-free mice had fewer of them.
The germ-free mice also had fewer stemlike cells that can differentiate into some types of immune cells. Plus, their spleens contained defective innate immune cells whose populations never reached the size found in healthy mice with microbes in their gut.