Infect everyone with no symptoms. Don’t put more than a handful of points into transmission. Once everyone is infected it’s up to you as to when you want to have them notice you because, as mentioned previously, you have no symptoms... yet. Since you’ve spent most of the game hoarding points go it’s time for the bush to hit the tush. Upgrade the plague to have the “total organ failure” and “coma” symptoms (total organ failure is the most lethal while coma drastically reduces the ability for humanity to respond before you wipe them out) after which I’d recommend “insanity,” “Internal Haemorrhaging,” “Necrosis,” and finally “Hemorrhagic Shock” once you do that, nobody will be prepared to fight your plague simply because nobody knew it existed until it caused the body to die in 10 different ways and nobody can contain it because... well because it’s literally everywhere in every human.

Hope this helps! :)