its a cheaper than any WMD. Infect a moron here who was brainwashed and send him/her to a casino or a bar....have that person vomit all over the place. There you have it.
Get someone infected, have them travel to the US, keep them in isolation till they die. Get a half dozen or so fanatics to volunteer to spread the germs. Tell them you will vaccinate them so that they will be protected but only administer saline.
Then use the several “transmitters” to intentionally leave traces of body fluids on door knobs in bathrooms, theater exit doors, subway turn styles, ATM key pads, use the local prostitutes, etc, focusing on the top cities by population.
In a week, you would have the first wave of thousands. By the second week, you would have tens of thousands and your transmitters would likely be hospitalized. By the time the first wave of transmitters dies, hundreds of thousands would be infected.