A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

How long does a smallpox vaccination protect you?

November 9, 2001

Dear Cecil:

During the current anthrax scare, a report on the radio about various bioterrorism agents said the smallpox virus was a particularly nasty pathogen. I looked down at the smallpox vaccination scar on my arm and thought, "Well, that's one thing I don't have to worry about." But now I read that smallpox vaccinations only provide protection for seven to ten years! My vaccination was over 30 years ago, back in the 60s. Did my parents literally scar me for life for a measly seven to ten years of protection? I thought you only had to be vaccinated for smallpox once. If not, how come you see lots of old photos of folks with a single smallpox vaccination scar, but I can't remember ever seeing anybody with multiples? Certainly my parents only had one apiece. So what's the deal, Cecil? Are smallpox vaccinations only good for seven to ten years, or is that just being overly conservative?

Cecil replies:

I don't mean to raise undue alarm, but these are perilous times. Here are some things you should know about smallpox:

(1) Smallpox vaccination is effective for about ten years and provides diminishing protection thereafter. Booster shots normally weren't administered unless there was a danger of exposure, e.g., traveling overseas. In the U.S. routine vaccination ended in 1971, booster shots for international travel were discontinued in 1982, and public distribution of the vaccine ceased in 1983 (military personnel were vaccinated until 1990). This means that while there may be hope for Eric Clapton and B.B. King, it's curtains for Britney Spears.

(2) Nasty doesn't begin to do justice to this disease. Here's a description by medical journalist Richard Preston ("Demon in the Freezer," New Yorker, July 12, 1999):

Smallpox is explosively contagious, and it travels through the air. Virus particles in the mouth become airborne when the host talks. If you inhale a single particle of smallpox, you can come down with the disease. After you've been infected, there is a typical incubation period of ten days. During that time, you feel normal. Then the illness hits with a spike of fever, a backache, and vomiting, and a bit later tiny red spots appear all over the body. The spots turn into blisters, called pustules, and the pustules enlarge, filling with pressurized opalescent pus. The eruption of pustules is sometimes called the splitting of the dermis. The skin doesn't break, but splits horizontally, tearing away from its underlayers. The pustules become hard, bloated sacs the size of peas, encasing the body with pus, and the skin resembles a cobbled stone street. The pain of the splitting is extraordinary. People lose the ability to speak, and their eyes can squeeze shut with pustules, but they remain alert. Death comes with a breathing arrest or a heart attack or shock or an immune-system storm. (Full text at cryptome.org/smallpox-wmd.htm; icky photos at www.bt.cdc.gov/Agent/Sma llpox/SmallpoxImages.asp.)

Typically 25 to 50 percent of victims die; survivors are permanently scarred and sometimes blind. Humans are the only known carriers of smallpox; you can't get it from animals or insects.

(3) The last smallpox epidemic occurred in Bangladesh in 1975 but was contained within the year. The last known cases of smallpox, from accidental lab exposure, occurred in England in 1978. The World Health Organization declared — somewhat precipitously, you may think — that smallpox had been eradicated from the globe in 1980. Officially, the last vials of the smallpox virus are held in government labs in the United States and Russia.

(4) However, antiterrorism experts suspect that other nations have gotten their rubber-glove-clad hands on the stuff, possibly including China, Iran, Iraq, Israel, North Korea, Serbia, and Pakistan. Some believe that Osama bin Laden's organization and the Aum Shinrikyo cult in Japan also have some stashed.

(5) Richard Preston interviewed a former Russian bioweapons researcher who claimed that Russia had secretly manufactured and stored 20 tons of live smallpox virus, and who knows where it all is now?

(6) Manufacture of smallpox vaccine for general use halted in 1982. The U.S. currently has 15 million doses of vaccine on hand, a substantial portion of which has deteriorated and may no longer be effective. Preparations are underway to make another 54 million doses by next summer, and the government is negotiating for the manufacture of a total of 300 million doses, enough for everyone in the U.S. Until then many Americans are as vulnerable to smallpox as Native Americans were at the time of first European contact. Mass vaccination isn't something you want to undertake lightly, though.  It's estimated that if the entire U.S. population were vaccinated, 300 people would die due to adverse reactions.

(7) Diminished immunity or not, public health experts are counting on previously vaccinated people to care for the sick should a smallpox epidemic occur, hopefully after they've been revaccinated. These people are older, have kids, responsibilities, etc. But speaking as a fellow old fart, Mark, all I can say is, if the need arises, we're just going to have to suck it up.

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