People who worked with livestock didn't get the disease. Some other people figured out that cowpox made them immune. This was a very lucky thing, as smallpox was around for a long, long time. Anyway, this is a matter of a vaccine from a lesser form of the disease. Some vaccines use partially live virus, such as for the vaccine for shingles.
"Poliomyelitis, or infantile paralysis, was the most dreaded disease in the United States for much of the 20th century. Salk’s vaccine used inactivated, or “killed,” poliovirus to trigger an immune response against the disease. On April 12, 1955, officials announced the vaccine’s success and launched a nationwide immunization campaign. Within a generation, new cases of polio nearly disappeared."
Someone who wanted some fruit for those long sea voyages? A simple matter of diet.
Is this like the Lupus patients, either, who didn't get it?
Trump was a total fuck-up, from start to finish. Anything for a buck.