This game is great with updated rules and I realy enjoy it. Anyway after several plays I realized that there is one random element which can ruin your strategy/game/chance to win. If you draw same Tunnel Card(s) both or one turn after turn. Yes, it happens to me all the time no matter how much I shuffle cards. So I suggest the option in solo play to set aside the Tunnel Card you just played for the next turn.
I'd suggest you don't do that as you may require the same card again the next turn depending on the situation mid-game. Your idea would completely block that option if that situation presented itself. I've tried it and it happened to me.
My advice is to play solitaire but with two characters or more to mitigate that. It works really well, but bear in mind with more characters the virus can mutate more often. Its a balancing act!