by Brian C. Joondeph, M.D., American Thinker:

Natural immunity to disease is, or at least was, a well-known concept in medicine.

By disease, I mean viral infections. One can’t develop natural immunity to diseases like diabetes or heart failure. Many of us remember “chicken pox parties” where when one kid was infectious, he or she was invited over to play with your kids, so they all got infected and then they did not have to worry about getting chicken pox again, due to natural immunity.