Patterns of antibody response in humans to the anthrax vaccine adsorbed (AVA) primary (six-dose) series.

The antibody profile during and after the six-dose primary vaccination series with anthrax vaccine adsorbed (AVA, Biothrax) was characterized in 86 human volunteers. Ninety-three percent of recipients developed IgG antibodies to Bacillus anthracis protective antigen (PA) after two doses, and 100% were seropositive after dose #3. Geometric mean concentrations (GMC) of IgG to PA measured before and after each dose were significantly lower after injection #3 (peak GMC=146.65 microg/mL, trough GMC=15.16 microg/mL) than after injections #4 (peak GMC=430.46 microg/mL, trough GMC=94.57 microg/mL), #5 (peak GMC=415.05 microg/mL, trough GMC=81.94 microg/mL), or #6 (peak GMC=401.16 microg/mL, trough GMC=96.19 microg/mL) (p<or=0.0001 for each); but not between injections #4 and #5, #5 and #6, or #4 and #6 (p>or=0.7923 for each). Decay rates for IgG to PA were significantly faster after injection #3 (half life [T1/2]=39.21 days) than after injections #4 (T1/2=72.03 days), #5 (T1/2=70.14 days), and #6 (T1/2=74.59 days) (p<or=0.0282 for each). Toxin neutralizing assay (TNA) antibody patterns generally paralleled those for IgG to PA. The 6-month dose in the AVA primary series appears to be critical in sustaining IgG to PA concentrations in a substantial proportion of recipients.