Within three to four days, a red, raised and itchy spot develops at the vaccination site. This is a sign of “a take,” which means the vaccine is doing its job. This spot soon turns into a pus-filled blister that gradually gets a little bigger by day 10. Then, it slowly starts to dry out. As the blister heals, a scab develops. This is a normal part of your skin’s healing process. By 14 to 21 days after vaccination, the scab falls off. In its place, a small, pitted scar remains. my.clevelandclinic.org/…/smallpox-vaccine-scar