Hepatitis A virus is one of several hepatitis viruses that cause a systemic infection with pathology in the liver. The incubation period ranges from approximately 20 to 50 days. The course of the disease following infection ranges from asymptomatic infection to fulminant hepatitis and death.¹

Protection from hepatitis A disease has been shown to be related to the presence of antibody. Protection after vaccination with VAQTA has been associated with the onset of seroconversion (³10 mIU/mL of hepatitis A antibody, measured by a modification of the HAVAB ** radioimmunoassay [RIA]² ) and with an anamnestic antibody response following booster vaccination with VAQTA.

A very high degree of protection has been demonstrated after a single dose of VAQTA in children and adolescents.³ The protective efficacy, immunogenicity and safety of VAQTA were evaluated in a randomized, double-blind, placebo-controlled study involving 1037 susceptible healthy children and adolescents 2 through 16 years of age in a U.S. community with recurrent outbreaks of hepatitis A (The Monroe Efficacy Study). Each child received an intramuscular dose of VAQTA (~25U) or placebo. Among those individuals who were initially seronegative (by modified HAVAB), seroconversion was achieved in >99% of vaccine recipients within 4 weeks after vaccination. The onset of seroconversion following a single dose of VAQTA was shown to parallel the onset of protection against clinical hepatitis A disease.

Because of the long incubation period of the disease (approximately 20 to 50 days, or longer in children ⁴ ), the primary endpoint was based on clinically confirmed cases *** of hepatitis A occurring ³50 days after vaccination in order to exclude any children incubating the infection before vaccination. In subjects who were initially seronegative, the protective efficacy of a single dose of VAQTA was observed to be 100% with 21 cases of clinically confirmed hepatitis A occurring in the placebo group and none in the vaccine group (p<0.001). A secondary endpoint was pre-defined as the number of clinically confirmed cases of hepatitis A ³30 days after vaccination. With this secondary endpoint, 28 cases of clinically confirmed hepatitis A occurred in the placebo group while none occurred in the vaccine group ³30 days after vaccination. In addition, it was observed in this trial that no cases of clinically confirmed hepatitis A occurred in the vaccine group after day 16. † Following demonstration of protection with a single dose and termination of the study, a booster dose was administered to a subset of vaccinees 6, 12, or 18 month after the primary dose. To date, no cases of clinically confirmed hepatitis A disease ³50 days after vaccination have occurred in those vaccinees from The Monroe Efficacy Study monitored for up to 9 years.⁵

Although cases of imported infection have occurred, the study community has remained free of outbreaks, evidence for the effectiveness of VAQTA for use in community outbreak control. In contrast, three nearby sister communities to Monroe have continued to experience outbreaks.^{3, 6}

Other Clinical Studies

The efficacy of VAQTA in other age groups was based upon immunogenicity measured 4 to 6 weeks following vaccination. VAQTA was found to be highly immunogenic in all age groups.

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