No need to devolve symptoms. Use them to infect your start country, ignoring transmissions thus keeping mutation down in the beginning:
Rash, Sweating, Skin Lesions, Coughing, Sneezing
Now add some abilities (still keeping mutation down)
Drug1, Cold1, Heat1, Cold2, Heat2
Around this point you will be detected and you will get your first mutation. You only need to devolve if you mutate Necrosis.
Now transmissions
Air1, Water1, Air2, Water2, Ex Bio
And more abilities
Drug2, Env hardening, Gen hardening 1 + 2
Quickly infect the world by evolving all the level1 and 2 symptoms. You will get lots of DNA due to high severity. Now hang back for a short while, let the virus mutate. Only devolve if you get a highly lethal symptom.
When all countries are fairly infected use your 150-200 saved DNA and mutate some more symptoms. Hold back the very lethal ones until everyone is infected.
You will get another hundred DNA as people die. Use them at the very last moment for Genetic ReShuffle.
Humanity done in about a year.
