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Biosecurity News in Brief
Study Shows Smallpox Vaccine Effective in Diluted Doses, Could Increase StockpileBy Shana Deitch, February 16, 2007 The March 15, 2007 edition of the Journal of Infectious Diseases published a study[1] conducted to determine if diluted doses of smallpox vaccine offers effective protection from the disease.[1] In the investigation, researchers observed vaccination reactions among 330 individuals between 18 and 32 years of age to see if outward physical and immunologic reactions to the vaccine changed with the administration of a diluted dose. According to the study, existing U.S. stocks of smallpox vaccine consist of Wyeth Dryvax vaccine, prepared over 40 years ago, and Sanofi Pasteur vaccine, prepared for military use from 1956-7. Researchers administered smallpox vaccine to study participants born after the cessation of routine smallpox vaccination, to help ensure no prior history of [smallpox] vaccination. Participants received either undiluted vaccine or vaccine diluted in 1:3.2 (Sanofi Pasteur only), 1:10, 1:32, or 1:100 (Wyeth Dryvax only) solutions.[1] Participants were evaluated for reactions, or “takes,” to the vaccine, measured by the appearance of lesions at the injection site, and any associated pain, swelling, fever, rash, or adverse event. Serum neutralizing antibody assays were also performed. There were no significant differences in take rates in any of the groups. Take rates for individuals given undiluted vaccine and 1:3.2 dilution were 99.2% and 95.6% for those given 1:10 and 1:32 (Wyeth Dryvax and Sanofi Pasteur) and 1:3.2 and 1:10 (Sanofi Pasteur) dilutions. The take rate for individuals given 1:100 dilution vaccine was lower (83.3%), but this difference was not statistically significant. Most (97.5%) participants with a take developed an increase in serum neutralizing antibody levels, resulting in a highly significant correlation between take and antibody response for each vaccine dose. No antibody responses occurred in study subjects who did not experience a take.[1] There were also no significant differences in lesion size, pain at the injection site, or rash induced by the different vaccine types or different dilution levels. However, individuals given more concentrated doses of vaccine were significantly more likely to experience fever, headache, nausea, and fatigue leading to missed activity. Incidence of fever was reduced by two thirds and incidence of missed activity was reduced by approximately half in individuals who received less concentrated doses of vaccine. Study authors conclude that the level of immunity to smallpox from the administered doses of diluted vaccine “suggests that a dilution of 1:20-1:30 would be acceptable” for individuals with no vaccine history and that “[a] plan for use of higher dilutions would create an enormous stockpile of vaccine.”[1] Likewise, a diluted dosage of smallpox vaccine could reduce adverse reactions to the vaccine without compromising the success rate of vaccination.
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