10%

According to the CDC, if you have eczema, you shouldn’t be vaccinated for smallpox or come into contact with people who have been vaccinated. They estimate that about 27 million Americans have eczema– roughly 10% of the population. I’m no epidemiologist, but it would seem that if you can’t vaccinate 10% of your population that you are likely to have difficulty controlling the spread of a contagious disease.