Immunogenicity and safety of an inactivated hepatitis A vaccine in Taiwanese adults and children.

The safety and immunogenicity of an inactivated hepatitis A vaccine (AVAXIM, 160 antigen units) was evaluated in 190 subjects: 50 children aged from 2 to 5 years, 70 children aged from 6 to 17 years and 70 adults aged from 18 to 30 years in a monocentric, open, non-controlled, phase III trial conducted in Taipei, Taiwan from December 1996 to October 1997. The vaccine was administered intramuscularly, with a two-dose schedule 6 months apart. Clinical adverse events were monitored during the seven days following each injection. Hepatitis A virus (HAV) antibody titers were measured by modified radioimmunoassay on the day of inclusion and four weeks after both the first dose and booster injection. Among the 190 subjects who received the first dose, 174 (91.6%) were initially HAV seronegative and 16 (8.4%) were HAV seropositive at inclusion. One hundred and seventy-four subjects (91.6%) received the booster dose and completed the study. One month after the first dose, all the subjects, whatever the age, presented HAV antibody titers over 20 mIU/ml. In children (2 to 17 years), the GMT was 136 mIU/ml at week 4 and 7,906 mIU/ml four weeks after the booster dose. In adults (> or = 18 years), GMT values were 93 mIU/ml at week 4 and 3,655 mIU/ml four weeks after the booster. These results show a strong anamnestic response to the second dose of vaccine and are compatible with long-term antibody persistence in each age group. The vaccine was safe and well tolerated. No vaccine-related serious adverse event occurred. No immediate reaction occurred. The majority of the reactions were reported by adults after the primary injection. Local reactions (pain and redness) were reported by 9.0% and 4.0% of the subjects after the primary and the booster doses, respectively. Systemic reactions (mainly myalgia/arthralgia or asthenia) affected less than 10% of the subjects after the first dose and less than 3% after the booster. Results from this study in a Taiwanese population are consistent with those obtained with the same vaccine in previous European studies in children and adults, and suggest that AVAXIM (160 AU) is suitable for use in all subjects aged over 2 years.

Immunogenicity and safety of a new inactivated hepatitis A vaccine in Thai young adults.

In view of the increasing median age of hepatitis A virus (HAV) infection observed recently in Asia, and the resulting increased number of symptomatic cases occurring in adults, with the concomitant risk of outbreaks, immunization against this agent on a national scale might be considered. An open clinical trial was conducted in Thai adolescents and young adults in order to establish the immunogenicity and safety of a new inactivated hepatitis A vaccine. At 24-week intervals, two doses (primary dose and booster) of the hepatitis A vaccine (160 antigenic units per dose) were administered to 80 HAV-seronegative healthy volunteers, their ages ranging from 16 to 25 years. Local and systemic reactions were recorded within the first 7 days after each injection. Anti-hepatitis A virus antibody concentrations were measured by a modified radioimmunoassay before and one month after each injection. No serious adverse reactions were reported. Local reactions were confined to transient pain at the injection site, occurring within 24 hours after injection in 42.5% of the subjects after the first dose and 24.1% of the patients after the booster dose. Systemic reactions (particularly asthenia or myalgia) were observed in 35.0% and 8.9% of subjects after the first and the booster injection, respectively. Most of these reactions were transient. One month after the first dose, all 78 formerly seronegative subjects had attained satisfactory seroconversion levels of anti-HAV antibody concentrations (> or = 20 mIU/ml) which they maintained until the booster. The booster dose elicited a 21-fold increase of HAV antibody levels, with a geometric mean titer of 2,964 mIU/ml (95% CI, 2,467-3,560), indicative of long-term protection. This new inactivated hepatitis A vaccine appears to be safe and highly immunogenic upon administration of a primary dose followed by a booster dose after 24 weeks. In countries where socio-economic improvement has postponed hepatitis A infection from early childhood (mostly asymptomatic) towards adolescence and adulthood, with the symptoms increasing in severity, inclusion of inactivated hepatitis A vaccine in a preventive vaccination program might be of benefit.