The smallpox vaccine used at the time of eradication had two main issues: 1) In some (fairly small) fraction of recipients it lead to severe side-effects, inc

The smallpox vaccine used at the time of eradication had two main issues: 1) In some (fairly small) fraction of recipients it lead to severe side-effects, including death. 2) It was a live-virus vaccine, which meant a vaccine recipient could actually infect those around them (with the vaccine, effectively). This was a serious problem if anyone near the recipient was immune-compromised; the risk of deleterious side-effects in immune-compromised individuals, who would not be vaccinated normally) was much higher. There is a modern (a few years old!) smallpox vaccine that is a dead-virus vaccine and would have a very different cost-benefit tradeoff in medical terms. I don't know what the economic tradeoff looks like (i.e. how expensive it is).