Smallpox Vaccine - Shorts

Townsend Letter for Doctors and Patients,  Jan, 2002  by Jule Klotter

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Because of concerns that smallpox will be used as a bioweapon, the US government is seeking ways to stretch its stockpile of vaccine to cover more people. Routine vaccinations for US civilians ended in 1972, because smallpox had virtually disappeared from the country. Also, the vaccine, which was made by collecting pus from calves infected with a smallpox-related virus, caused adverse reactions in about 1 in 13,000 persons. People with weak immune systems are the most susceptible to these effects, which include severe rashes and encephalitis. The Centers for Disease Control and Prevention has ordered 40 million doses of a new vaccine, grown in human cells, from the British company Acambis.

In the meantime, the National Institute of Allergy and Infectious Diseases has been studying the possibility of diluting the stockpiled vaccine so that more people can be vaccinated. Tests, performed in 2000, compared volunteers' reactions to undiluted vaccine to the reactions of those receiving tenfold dilution or hundredfold dilution. By examining blood studies and checking vaccine sites on the arm for characteristic scabs and boils, scientists determined that the hundredfold dilution caused little response, but the tenfold dilution was about 70% effective. New studies will guage the effectiveness of tenfold and fivefold dilutions. Fivefold dilution, which is expected to be very effective, would stretch the current vaccine stockpile from about 15 million doses to 75 million doses, which would cover about one-fourth of the US population. Having never studied how long immunity from the vaccine lasts, scientists are unsure about the level of protection available to persons who received smallpox vaccinations be fore 1972.

"US Acts to Make Vaccines and Drugs Against Smallpox" by William J. Dread. The New York Times, October 9, 2001

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