An open study of subcutaneous administration of inactivated hepatitis A vaccine (VAQTA) in adults: safety, tolerability, and immunogenicity.

A number of patients in clinical practice would be candidates for hepatitis A vaccine administered subcutaneously (SC), including patients with inherited and acquired coagulopathies. To assess the safety, tolerability, and immunogenicity of VAQTA (Hepatitis A Vaccine, Inactivated, Merck and Co. Inc., West Point, PA) was administered SC to healthy adults. A total of 114 healthy adults received two doses of vaccine SC 24 weeks apart. No serious vaccine-related adverse experiences were reported. Four weeks after dose 1, the seropositivity rate (SPR) was 77.9% (CI, 69.1, 85.1%). The geometric mean titer (GMT) was 21.0 mIU/ml. Twenty-four weeks after dose 1 (just prior to dose 2) and 28 weeks after dose 1 (4 weeks following dose 2), the SPRs were 95.3% [corrected] and 100%, respectively; the GMTs were 153.2 and 1563.9 mIU/mL, respectively [corrected]. Although the kinetics of the immune response were slower when VAQTA was administered SC compared to intramuscular injection, SPRs and GMTs increased over time, indicating that the vaccine administered SC demonstrated immunogenicity.