Duration of Protection of Rabbits after Vaccination with Bacillus anthracis Recombinant Protective Antigen Vaccine
ARMY MEDICAL RESEARCH INST OF INFECTIOUS DISEASES FORT DETRICK MD BACTERIOLOGY DIV
Pagination or Media Count:
Long-term protection of rabbits that had been vaccinated with two doses of a recombinant protective antigen rPA vaccine was examined against an aerosol spore challenge with the Ames isolate of Bacillus anthracis at 6 and 12 months. At 6 months after the primary injection, survival was 74.1 2027 with quantitative ELISA titer of 22.3 microg of anti-rPA IgG per millilitre and toxin neutralizing antibody TNA assay titer of 332. At 12 months after the primary injection, only 37.5 924 of the rabbits were protected with quantitative ELISA titer of 19.8 microg of anti-rPA IgG per millilitre and TNA assay titer of 286. There was a significant loss of protection p 0.0117 and a significant difference in survival curves p 0.0157 between the 6- and 12-month groups. When ELISA or TNA assay titer, gender, and challenge dose were entered into a forward logistic regression model, week 26 ELISA titer p 0.0236 and week 13 TNA assay titer p 0.0147 for the 6-month group, and week 26 ELISA titer p 0.0326 and week 8 TNA assay titer p 0.0190 for the 12-month group, were significant predictors of survival. Neither gender nor challenge dose were identified as having a statistically significant effect on survival. Booster vaccinations with rPA may be required for the long-term protection of rabbits against anthrax.