Q: What is smallpox and why is it so worrisome?
A: Smallpox is a highly contagious virus that is spread from person to person, historically killing 30 percent of its victims. People can prevent infection if vaccinated within four days of exposure, before symptoms even appear; afterward, it's too late, and there is no known treatment. The last case of smallpox in the United States was in 1949, and routine vaccinations ended in 1972. That means that some 45 percent of the public is totally unprotected. People vaccinated decades ago may have some residual protection, but health officials aren't sure.
Bioterrorism experts paint frightening scenarios like this: A dozen people on a suicide mission infect themselves with smallpox and, when they are at their most contagious, walk around airports, infecting hundreds of others who then carry the virus across the country.
Q: Wasn't smallpox wiped out?
A: In 1980, the disease was declared eradicated worldwide, and all samples of the virus were to have been destroyed -- except those held by special labs in Atlanta and Moscow. Experts fear some of the Russian sample could have escaped to hostile nations, fears that are amplified as the United States contemplates war with Iraq.
Q: Why not just vaccinate everyone right now?
A: The smallpox vaccine is very effective, so the Bush administration is planning to offer it widely. But many are urging caution because the vaccine itself, made with a live virus called vaccinia, carries rare but serious risks.
Q: How many people could be hurt by taking the vaccine?
A: 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. If a smallpox attack never comes, that would be a heavy toll to pay. Reactions are less common for those revaccinated.
For the approximately 130 million Americans never vaccinated, experts would expect nearly 2,000 to face life-threatening complications and 125-250 of them to die.
For about 158 million people being revaccinated, experts expect nearly 800 life-threatening complications and about 40 deaths.
Q: What sort of reactions and complications?
A: Typical reactions include sore arms, fever and swollen glands.
The most common serious reaction comes when vaccinia escapes from the inoculation site, often because people touch the site and then themselves or someone else. For instance, the virus transferred to the eye can cause blindness.
More deadly is encephalitis, which can cause paralysis or permanent neurologic damage. Also fatal though very rare: progressive vaccinia, where the vaccination site does not heal and the virus spreads, eating away at flesh, bone and gut.
Q: Who's at greatest risk of complications?
A: People with weak immune systems -- those with HIV, cancer and transplanted organs -- face much greater risk, as do pregnant women. People with eczema risk a serious, permanent rash. Officials administering the vaccine will ask detailed questions to try to screen out such people.
Q: If the vaccine is effective four days after exposure, why not just vaccinate after an attack?
A: Delivering mass vaccinations within days is incredibly complicated, and an attack would be much less deadly if there is more vaccination now. However, planning is also under way for post-attack vaccinations.
Q: Is there enough smallpox vaccine for everyone?
A. Yes. Studies have shown that the already available vaccine can be diluted, meaning there is enough for everyone in the United States. New vaccine should arrive by the end of the year.
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