[CPOSharky]

The article does not discuss natural immunity except in passing. What percentage of the population is naturally immune?

I know I am, of the many smallpox immunizations I had none had any effect. The next day the immunization site was indistinguishable from normal skin.

[FormerLurker]

What percentage of the population is naturally immune?

I'm not really sure. I've seen estimates ranging from 0-90%. So, who knows. I'll see what I can find in the way of information on that if I can...