So I was thinking how could American Indians be spared from the ravages of old world diseases like smallpox and measels. The only logical way I could come up with is European science defeating these illnesses before Columbus sets sail. Is this possible or ASB?
This will not prevent the spread of the diseases to the New World. It would not be possible at that time to eradicate the diseases 'in the wild'.
OTOH, Edward Jenner did all that innoculation with cowpox vaccine in the 18th Century, and while he didn't eradicate smallpox 'in the wild' he certainly reduced the number of deaths.