Endgame Texts/Final Loss
You have lost your only chance to recover the information needed to create a vaccine for the alien infection. Your researchers try their best regardless, but what they manage to do is too little too late. The infection spreads steadily across the entire globe until humanity is reduced to a handful of terrified individuals, always on the run until they are hunted down like animals and given their injection.
When the aliens are done, Earth is left a barren wasteland, and humanity as a free-thinking species is extinct.