As it was completing its work, the committee received information about a record-linkage study at the DoD Center for Deployment Health Research by Ryan and colleagues (Ryan, 2002) of the risk of birth defects among children born to women in the military who were vaccinated with AVA. Although the analysis was not complete as of February 2002, preliminary results suggesting a possible increase in risk were noted in the January 2002 revision of the product insert for AVA and in informed-consent documents provided in December 2001 to individuals who were offered vaccination with AVA as supplemental prophylaxis following possible exposure to anthrax spores in the autumn 2001.

The analysis compares the prevalence of birth defects among children born to women in the military who received AVA during the first trimester of pregnancy with the prevalence of birth defects among children of military women who received AVA at any other times, according to records in the DoD Birth Defects Registry and the DoD database that stores information on AVA immunizations given to military personnel. Established in 1998, the DoD Birth Defects Registry contains information on infants with birth defects (ICD-9-CM codes 740.0–760.71) diagnosed within the first year of life (Ryan et al., 2001). The registry data are captured from databases on DoD-financed hospitalizations and ambulatory care in military and civilian facilities.

For the period 1998-1999, approximately 3,000 infants were born to military women with a record of having received at least one dose of AVA. Comparisons were adjusted for maternal age, race, marital status, service branch, rank, and occupational group. No quantitative results from this study were available to the committee, but they were reported to indicate a small but statistically significant association between anthrax vaccine exposure in the first trimester of pregnancy and the frequency of birth defects diagnoses.