Heavily diluted doses of existing smallpox vaccine remain effective, which means the U.S. stockpile of the vaccine can be stretched if needed, researchers said Tuesday.
Smallpox is a highly contagious viral disease that killed untold millions until it was officially eradicated in 1979, but fears following the September 2001 attacks that it might be used as a biological weapon sparked a U.S. effort to ensure there was enough vaccine.
A large portion of the available smallpox vaccine in the United States has been frozen since it was manufactured in the 1950s. The U.S. government has contracted with Britain’s Acambis Plc to supply millions more new doses.
While vaccinations have not been recommended for the general public due to potentially lethal side effects in rare cases, tens of thousands of front-line military and health-care workers have been vaccinated.
Study confirms previous research
In the study, published in this week’s Journal of the American Medical Association, volunteers aged 18 to 32 were given one of three strengths of smallpox vaccine. The weakest was diluted to one-tenth the original, and nearly all developed a telling pustule at the inoculation site within six to 11 days, indicating the dosage’s effectiveness.
The study confirmed previous research that showed diluted versions of the vaccine were effective.
“This allows for amplification of the current smallpox vaccine stockpile (approximately 85 million doses of Aventis Pasteur smallpox vaccine) if needed,” wrote study author Thomas Talbot of Vanderbilt University School of Medicine, in Nashville, Tenn.
All but one of the 340 volunteers in the study developed post-vaccination symptoms, including itching or pain at the inoculation site. Fatigue, muscle pain and headache were also common and one in five suffered a fever, the report said.
Five of the volunteers reported “cardiac symptoms” that went away without complications, it said.
The study was completed just before the U.S. military reported in February 2003 a few adverse cardiac reactions believed related to its effort to vaccinate 500,000 personnel against smallpox and anthrax.
A small number of U.S. troops refused to be vaccinated due to worries about side effects, and some have been discharged for refusing.
The smallpox vaccine uses a live virus related to smallpox called vaccinia, and it can spread to other people. When widely used, it killed one to two out of every million people who received it and caused side effects ranging from a rash to a swelling of the brain called encephalitis.
Smallpox kills about 30 percent of its victims and scars the remainder for life.
