Immunogenicity and estimation of antibody persistence following vaccination with an inactivated virosomal hepatitis A vaccine in adults: A 20-year follow-up study.

PURPOSE: This was a 20-year follow-up study to assess long-term persistence of protective antibody levels against the hepatitis A virus (HAV) in healthy participants vaccinated with 2 doses of inactivated hepatitis A vaccine (Epaxal®) between 1992 and 1995. METHODS: Blood samples for anti-HAV antibody concentrations were obtained during a follow-up visit 20years after vaccination and were analyzed in parallel with samples still available from previous visits using AxSYM® HAVAB 2.0 assay. RESULTS: Mean (SD) age of the participants was 44.71 (3.905) years at year 20 follow-up (N=95). Participants completing 0/12-month Epaxal® immunization regimen (N=94) had seroprotection rate of 100% (95% CI: 96.2, 100.0) with ⩾10mIU/mL seropositivity cut-off and 98.9% (95% CI: 94.2, 100.0) with ⩾20mIU/mL cut-off. With ⩾10mIU/mL cut-off, the estimated median duration of protection was 77.3years (95% CI: 71.8, 83.5) with 95% of the vaccinated participants predicted to be protected for at least 41.5years. At ⩾20mIU/mL cut-off, the estimated median duration of protection was 64.8years (95% CI: 60.1, 68.4) with 95% of the vaccinated participants predicted to be protected for at least 33years. Anti-HAV antibody geometric mean concentrations were higher in women (277.9; 95% CI: 217.7, 354.7) than in men (167.7; 95% CI: 125.2, 224.6). CONCLUSION: The data from this 20-year follow-up study confirm previous observations that two doses of Epaxal® provide protection against hepatitis A infection for at least 30years in over 95% of healthy participants.

Stability studies of binding and functional anti-vaccine antibodies.

BACKGROUND: As most vaccines exert their protective capacity by eliciting pathogen-specific antibodies, antibody assays assessing immunogenicity of vaccines in development should be well characterized. Part of the validation of immunogenicity assays for vaccines is the study of stability of antibodies in serum. Materials & methods: Stability of antibodies in human serum was assessed by circumsporozoite-binding IgG ELISA designed for assessing the immunogenicity of a malaria vaccine under development, adenovirus neutralization assay, designed to assess neutralizing antibodies against adenovirus and commercially available test kits for hepatitis A and B. RESULTS: Stability studies indicated stability of serum-binding IgG antibodies and serum-neutralizing antibodies in: long-term storage below -65°C and -20°C; short-term storage; multiple freeze/thaw rounds; during shipment; and during heat inactivation. CONCLUSION: RESULTS have shown the stability of both binding and functional polyclonal antibodies in human serum under stable storage and common usage circumstances.