Apparently, Dr. Allen has cancer, which would be the main reason he got into doing that research. Asthma is a bit more common, so perhaps he lucked out. Or, another option, enough time has passed, and the gas has dissipated or fallen harmlessly to earth.
There were some in Hazmat suits and sealed rooms at the CDC, where Dr. Allen spent Wednesday. I'm going to say one of two things, either Dr. Allen just said the CDC was coming to hopefully avoid being called on it, or he really did call them, and they are on their way.