title: Duration of protection of rabbits after vaccination with Bacillus anthracis recombinant protective antigen vaccine.
abstract: 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% (20/27) 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% (9/24) 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.
authors.affiliation: United States Army Medical Research Institute of Infectious Diseases, Bacteriology Division, 1425 Porter Street, Fort Detrick, Frederick, MD 21702-5033, USA. stephen.little@amedd.army.mil
authors.forename: S F
authors.initials: SF
authors.lastname: Little
authors.forename: B E
authors.initials: BE
authors.lastname: Ivins
authors.forename: W M
authors.initials: WM
authors.lastname: Webster
authors.forename: P F
authors.initials: PF
authors.lastname: Fellows
authors.forename: M L M
authors.initials: ML
authors.lastname: Pitt
authors.forename: S L W
authors.initials: SL
authors.lastname: Norris
authors.forename: G P
authors.initials: GP
authors.lastname: Andrews
mesh_terms: D000818:Animals; D000881:Anthrax / Q000276:immunology / Q000517:prevention & control*; D022122:Anthrax Vaccines / Q000008:administration & dosage* / Q000276:immunology; D000907:Antibodies, Bacterial / Q000096:biosynthesis* / Q000378:metabolism; D000942:Antigens, Bacterial / Q000276:immunology; D001408:Bacillus anthracis / Q000737:chemistry* / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D011817:Rabbits; D013997:Time Factors; D014611:Vaccination; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000276:immunology
chemical_list: D022122:Anthrax Vaccines; D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D014614:Vaccines, Synthetic