>>113731939he'd go into his fortress of solitude an find a vaccine.
Then he'll wonder if it would make humanity too dependant on him and so he thinks he should not use it.
While he's reflecting on it one of his villains will attack a laboratory that's working on the vaccine to steal it. He'll go fight them, t hen he'll somehow find out that Luthor had already developed the vaccine 10 years earlier because he had created the virus as an anti-Superman weapon, but a partner in crime had stolen it, then somehow Brainiac is involved and spread the deadly virus to all humans.
Then a fist fight happens and Luthor wants to use the vaccine himself but has to concede the vaccine to Superman who uses his superbreath to immunize all humans at once.
