Monthly Update: Anti-infectives: VAQTA: Merck's hepatitis A vaccine, purified, inactivated

Abstract

The safety/tolerability profile, immunogenicity and protective efficacy of VAQTA, Merck's hepatitis A vaccine, purified, inactivated, are based on studies of 18,239 vaccinees; 12,000 2–17 years and 6239 18 years and older. To date, no vaccinee has had any serious vaccine-related adverse experience. In placebo-controlled studies, the local and systemic adverse experience profile has been indistinguishable from that of placebo alum diluent. The goal of ≥ 95% seropositivity was achieved within 4 weeks after one im dose of 25 units (2–17 year olds, 1 U ≥1 ng of purified viral protein; 18 –76 year olds, 50 U). Anamnestic responses to a booster given at 6,12 or 18 months revealed that the priming dose conferred immune memory in > 99% of vaccinees, regardless of pre-booster antibody level.

Protective efficacy of 100% starting at least as early as day 21 after a single dose was proven in a randomised, double-blinded field trial among 2–16 year olds in Monroe, NY. Although prior to the vaccine trial cases occurred in each of the five pre-trial years, to date (11/95) no vaccinee has developed hepatitis A (despite cases in non-vac-cinees visiting or resident in the locality) since the trial ended in November 1991. Cases have appeared each year in three similar non-vaccinated communities. VAQTA has proven to be a highly protective, well tolerated hepatitis A vaccine. Since immune memory provides long-term protection against recurrent hepatitis A in those previously recovered from hepatitis A, the immune memory generated by VAQTA will probably provide very long-lasting protection.