title: A randomized study of a flexible booster dosing regimen of VAQTA in adults: safety, tolerability, and immunogenicity.
abstract: BACKGROUND
  VAQTA (hepatitis A vaccine inactivated, Merck & Co., Inc., West Point, PA) is licensed for use in healthy adults in a two-dose schedule at 0 and 6 months.
  
  
  OBJECTIVE
  to determine whether the responses to a booster dose of VAQTA administered to adults 12 or 18 months after the first dose were similar to the response when the booster dose was administered 6 months after the first dose.
  
  
  METHODS
  healthy adults were randomized to receive 50-U of VAQTA at 6 (Group I), 12 (Group II), or 18 months (Group III) following receipt of Dose 1 on Day 0. Blood samples were collected immediately prior to Doses 1 and 2 and then, 4 weeks following Dose 2. Seropositivity rates (SPRs), geometric mean titers (GMTs) in milli-international units per milliliter (mIU/ml) and booster response rates (BRRs) were compared among treatment groups. Safety data were collected on Vaccination Report Cards.
  
  
  RESULTS
  no serious adverse experiences were reported, and the vaccine was well-tolerated by subjects in the three treatment groups. One month following the booster dose, SPRs and GMTs for Groups I, II, and III, respectively, were, 100% (102/102) and 6726.4 mIU/ml; 97.9% (93/95) and 4863.8 mIU/ml; 100% (86/86) and 6068.3 mIU/ml. The BRRs were 88.2% (Group I), 90.2% (Group II) and 94.2% (Group III).
  
  
  CONCLUSIONS
  responses to the booster dose were comparable regardless of the timing (i.e. 6, 12, or 18 months following Dose 1). Flexibility in the timing of the booster dose of VAQTA in adults would allow the vaccination schedule to be the same for adults, adolescents, and children and may increase the likelihood that adults receive the booster dose.
authors.affiliation: Orlando Regional Healthcare, Orlando, FL, USA.
authors.forename: R
authors.initials: R
authors.lastname: Hornick
authors.forename: R
authors.initials: R
authors.lastname: Tucker
authors.forename: K M
authors.initials: KM
authors.lastname: Kaplan
authors.forename: K A
authors.initials: KA
authors.lastname: Eves
authors.forename: D
authors.initials: D
authors.lastname: Banerjee
authors.forename: E
authors.initials: E
authors.lastname: Jensen
authors.forename: B
authors.initials: B
authors.lastname: Kuter
mesh_terms: D000328:Adult; D004306:Dose-Response Relationship, Immunologic; D004890:Erythema / Q000209:etiology; D006261:Headache / Q000209:etiology; D035922:Hepatitis A Antibodies; D022362:Hepatitis A Vaccines / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D006508:Hepatitis Antibodies / Q000096:biosynthesis; D006801:Humans; D007115:Immunization Schedule; D007117:Immunization, Secondary; D010146:Pain / Q000209:etiology; D012449:Safety
chemical_list: D035922:Hepatitis A Antibodies; D022362:Hepatitis A Vaccines; D006508:Hepatitis Antibodies