"And vaccines work because they teach immune systems to recognize — and so more effectively resist — pathogens before the actual bug is encountered." Is a bold claim that has yet to be proven empirically.
Isn't that just the definition of a vaccine?
"A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease." ... "The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future."