Neat ideas! The Possums sound very deadly, but very helpful at the same time! It seems like this is a pretty infectious disease, so it'd be interesting to see how other players planned around it.
When you act with "each pair of revealed cards", I take that to mean you use the cards in every possible combination (e.g. if you have 3 cards, ABC, you would take actions for the pairs AB, AC, and BC)? With a maximum of 5 cards in hand, I assume that only using each card in a single pairing would be too limiting in actions.
I did find the board a little busy, partly because of the slight differences before and after finding the Cure. I wonder if it would make sense for the Action Glossary and the Action lists to be put on double-sided cards? They would start on the "Searching for Cure Actions" side and explain all the steps about Evidence. Then, when the Cure is found, both cards could get flipped to the "Cure if Found" side that explains how to develop and distribute the Cure. You could probably get rid of the Cure tracker too, since the cards would indicate the state of the game. Not sure if it's important to see all of the possibilities at all times, but just a suggestion.