Both smallpox and the vaccine that prevents it are scary. Which is worse?
Highly contagious, smallpox historically has killed 30 percent of its victims. Victims develop an extensive rash and high fever, vomiting and headache.
Sores begin in the mouth and throat, then a rash appears on the skin, beginning on the face and spreading to the arms and legs and then to the hands and feet. The rash then becomes raised bumps that are filled with a thick opaque fluid. The bumps become pustules, which then turn into scabs.
People who survive smallpox are often left with disfiguring scars.
No one knows the likelihood that smallpox will reappear, or that any particular person will become infected.
Most people do not have serious reactions, but based on studies from the 1960s, experts estimate that 15 out of every million people vaccinated for the first time will face life-threatening complications, and one or two will die. Reactions are less common for those revaccinated.
Typical reactions include sore arms, fever and swollen glands. About one in 10 people will experience extreme discomfort, with fatigue, loss of appetite and other flu-like symptoms that last a day or two.
Deadly reactions include encephalitis, which can cause paralysis or permanent neurological damage, and progressive vaccinia, where the vaccination site does not heal and the virus spreads, eating away at flesh, bone and gut.
Certain people are at particular risk of complications and should not be vaccinated absent a known threat. Among them: people with weak immune systems -- those with HIV, cancer and transplanted organs -- and pregnant women. People with eczema risk a serious, permanent rash.