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Biosecurity News in Brief
Study Finds Greater Risks Associated with European Smallpox VaccineBy David Press, September 8, 2006 On August 22, 2006, the journal Public Library of Science (PLoS) Medicine e-published a research study indicating that the European smallpox vaccine may have higher morbidity and mortality to that of its U.S. counterpart due to vaccine strain-related differences.[1] The smallpox vaccine is derived from the vaccinia virus, a variant of the milder cowpox virus. The virus has two major strains that are most widely used in the production of the smallpox vaccine, the Lister strain and the New York Board of Health (NYCBH) strain. The article notes that previous studies have shown a risk of death from smallpox vaccination to be approximately one person per million for any person vaccinated, but an investigation of strain-specific adverse reactions suggests that this estimate may not be broadly applicable to all strains.[1] Studies pointing to the one death per million figure had previously been performed almost exclusively on the NYCBH strain, and these numbers were then extrapolated to the Lister strain. However, statistical evidence performed by investigators appears to indicate that the Lister strain, stockpiled in several European nations—including England, Germany, and the Netherlands—has a greater risk of death (8.4 deaths per million vaccinated) than the U.S. stockpiled NYCBH strain (1.4 deaths per million vaccinated).[1] A greater risk of the most deadly complication, encephalitis, was associated with the Lister strain (26.2 cases per million); the NYCBH strain caused just 2.9 cases per million.[1] Additionally, the researchers found that the risk of death is not the same for all ages, as previously suspected. Children younger than one year who were inoculated with either vaccine had the highest mortality, while children at two years of age had the lowest mortality.[1] Based on these findings, the researchers also calculated expected mortality rates should mass vaccination campaigns be held in the Netherlands (with a population of 16 million) and Germany (with a population of 82 million). Although both of these countries have stockpiled Lister-strain smallpox vaccines, the researchers found that the using the NYCBH strain would result in fewer deaths in both countries. In the Netherlands, mass vaccination with the NYCBH strain would result in 9.8 deaths per million vaccinations, as compared with 55.1 deaths per million vaccinations with the Lister strain. In Germany, mass vaccination with the NYCBH strain would result in 46.2 deaths per million vaccinations, versus 268.5 deaths per million vaccinations with the Lister strain. The article notes that since there has been no major mass vaccination of people since the 1970s, the risk of morbidity and mortality may be underestimated with either of the vaccines due to patients’ health status at time of inoculation. The researchers cite that the only mass vaccination campaign currently underway in the U.S. is with military personnel, but those vaccinees are often younger and healthier than the general population—a factor which reduces the risk of complications from inoculation. Due to these factors, the researchers stated that, “policy makers planning… in Europe should be aware of the increased risk of adverse events associated with vaccination with the Lister strain, compared with the NYCBH strain.”[1] References
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