Safety and effectiveness of the new inactivated hepatitis A virus vaccine.

PURPOSE

To examine the evidence concerning the safety and effectiveness of the inactivated hepatitis A virus vaccine recently licensed for use in Canada.

DATA SOURCES

The main source of information were papers presented at the International Symposium on Active Immunization against Hepatitis A, held in Vienna, Austria, Jan. 27-29, 1992. The bibliographies of these papers were searched for additional references. Recent articles describing the new vaccine and the epidemiologic aspects of infection with hepatitis A virus (HAV) were also reviewed.

STUDY SELECTION

Peer-reviewed reports of trials approved by a government regulatory agency on the safety, immunogenic properties and efficacy of the vaccine.

DATA EXTRACTION

The authors assembled key reports on adverse reactions, protection from disease and serologic assessment of immune response in vaccine recipients; data from these reports were tabulated and analysed.

RESULTS OF DATA SYNTHESIS

The new vaccine contains the HM175 strain of HAV, which is adapted to grow in tissue culture. The virus is purified, inactivated with the use of formaldehyde and adsorbed onto aluminum hydroxide. The recommended dose for adults is 720 enzyme-linked immunosorbent assay (ELISA) units in a 1.0-mL dose and for children 360 ELISA units in a 0.5-mL dose, injected intramuscularly. The usual schedule is three serial doses, the second given 1 month and the third 6 to 12 months after the initial dose. Reported side effects are infrequent and minor. In healthy persons who have received two doses, the seroconversion rate is almost 100%. Protective efficacy after two doses is estimated to be 94%. However, the persistence of protective antibodies has been studied only over the short term (3 years).

CONCLUSIONS

The new HAV vaccine is safe, effective and best suited to pre-exposure prophylaxis in people with an increased risk of infection for an extended period, such as travellers to areas where the disease is endemic. Further studies are needed to determine whether infants respond well to the vaccine and whether the vaccine protects recipients from subclinical infection and associated fecal shedding of HAV. Controlled trials to determine the duration of protection beyond 3 years and the effects of more rapid dosage schedules are also needed.