Basically what I do is first of all upgrade fully the transmissions (usually only the air, insect, and water to full) Then, by that time, your disease will probably have been discovered, so while you wait for the rest of the world to get infected, you upgrade drug resistance, dna scrambling/whatever its called, that whole cluster thing and the hot and cold resistance. Then when everyones infected, upgrade the symptoms. Note that not
everything has to be fully upgraded as thats impossible.