From what I understand, Primers are made up of the cup, compound and anvil and are coated with a very thin moisture barrier. They are almost impervious to water and humidity. I found primers that were hidden in the back of my reloading bench drawer that I had for years, put them in some ammo just for range shooting and didn't have any misfires.
Oil is the biggest culprit for primers. Be it gun oil, skin oil or any other type.
As for CCIs, thats all I use and haven't had a problem in over 20 yrs.