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Regarding the study of vaccinations and subsequent optic neuritis by the Centers for Disease Control and Prevention (CDC),1 the authors made a curious choice of statistical methods. They had access to the Defense Medical Surveillance System (DMSS), an extremely rich database that includes all immunizations, diagnoses for all inpatient and outpatient medical encounters, and additional information for more than 10 million military person-years.
Instead of using this database to perform a highly powered study, a case-control method was chosen, although this method is known to provide relatively weak evidence and is often subject to bias, especially in the selection of controls. The study's power was reduced further by restricting the duration of analysis to 6-, 12-, and 18-week periods following vaccination rather than leaving open-ended the period during which optic neuritis cases were diagnosed after vaccination. In 2003, a congressionally mandated Institute of Medicine report urged the CDC to use the Defense Medical Surveillance System database to assess the relationship between anthrax vaccine and adverse health outcomes, but the Institute of Medicine asked for longer-term follow-up than even the period of military service, not 18 weeks.2
Because soldiers generally receive anthrax and smallpox vaccines immediately prior to 6-month deployments to Iraq or Afghanistan and access to ophthalmologists is limited in those areas, delays in diagnosis should have been expected. Furthermore, 64 soldiers who developed optic neuritis but had not completed 18 weeks of military service prior to diagnosis were excluded from the analysis. Yet soldiers receive a large number of immunizations during basic training, so those who developed optic neuritis early in their military careers were arguably the most likely to have vaccine-related illness.
According to Table 1, men comprised 69% of cases but only 31% of controls. Additionally, the authors acknowledged statistically significant differences in age and race between cases and controls. Because sex, race, and age affect the risk of developing optic neuritis, it is clear that the control group, whose method of selection is not explained, was never properly matched to cases.
A March 18, 2005, report from the CDC's National Immunization Program discussing the CDC's anthrax vaccine research portfolio states, “These anthrax vaccine safety trials will enhance the safety, knowledge, and acceptability of anthrax vaccine in the US military.”3
This leads one to wonder if the result was a foregone conclusion. In any event, the article's flaws negate its value. Editors should be wary of methods that fail to make use of all available data.
Correspondence: Dr Nass, Mount Desert Island Hospital, 10 Wayman Ln, Bar Harbor, ME 04609 (mnass@gwi.net).
Financial Disclosure: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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