My only issue with the obvious, is....its obvious. When we think "chemical reactions" within the story so far the main two that come to mind are:

1- Saul and Tanya's antibiotic concoction.
2-Michaels homemade "knock you out" concoction.

while both could play a part...i kinda hope they don't. While we could get some questions answered based on that...i don't know, I guess Id like bigger answers. It really can't be as simple as "mix these two drugs you typically wouldn't, boom...immunity"...that doesn't really work for me..