It doesn't affect natural immunity. It's not a vaccine because the immune system learns nothing. Egg yolk antibodies bind to pathogens like human antibodies. But the other side of the antibody, that informs the immune system that a pathogen was found, is different and gets ignored by the human immune system. These antibodies are used for super food that, for example, fights bacteria that hurt the stomach. There is nothing new about it. This study used spike proteins because everything around SARS works like a magnet for funding and attention.