Frankly, smallpox really wasn't needed to do the job. Chickenpox, measles, mumps,... the ordinary diseases were deadly to the American Indians.
Then, think of the guys handing out the blankets? Wouldn't they get smallpox as well? Most folks who had been vaccinated still didn't mess with smallpox. There were sub-varieties of it that didn't necessarily succumb to the anti-bodies produced in response to innoculation.
Most of the big die-offs were done with by the winter of 1648. Over the next two centuries small groups of isolated individuals would catch up to the plague. Some of this was observed by Lewis and Clark.
My grandfather grew up on an Oklahoma Cherokee Reservation. His father was an Indian Agent.In the 60s and 70s, the facts of history were still readily available, and taught in US schools.Now, the truth is as obscured as the Jewish hollocaust deniers wish their version could be accepted.
I could wish the tribal/reservation Indians had as powerfull an ethnic presense to force the truth to remain obvious.But the "indians" are mostly dead now.I will not play a research game with you to prove the truth.You appear not to be a serious history expert. You may claim whatever you wish.Repetition does not make it fact.