The purpose of this study is to compare the immunogenicity and safety of three different immunization schedules of inactivated hepatitis A vaccine (HAV) and/ or combined hepatitis A and B vaccine (HABV) in healthy Chinese infants.

This study is a randomized double-blind, single-center, phase IV clinical trial. The purpose of this study is to compare the immunogenicity and safety of three different immunization schedules of inactivated hepatitis A vaccine (HAV) and/ or combined hepatitis A and B vaccine (HABV) in healthy Chinese infants between 18 and 24 months old. The subjects were randomly assigned into 3 groups. Subjects in group 1 each received 2 doses of HAV with a 6-month interval (at day 0 and month 6); subjects in group 2 each received 1 dose of HAV at day 0 and 1 dose of HABV at month 6; subjects in group 3 each received 2 doses of HABV with a 6-month interval (at day 0 and month 6).

Inclusion Criteria:

• Healthy infants between 18 and 24 months old;
• Have not received hepatitis A vaccine before;
• Completed hepatitis B vaccine full immunization schedule;
• Written consent of the guardian of each participant;

Exclusion Criteria of the First Injection:

• History of allergy to vaccine(s), or history of serious adverse reaction to vaccination, such as urticaria, dyspnea, angioneurotic edema, or abdominal pain;
• Autoimmune disease or immunodeficiency;
• Any acute disease that made the conditions of the person unsuitable for vaccination
• Administration of any live attenuated vaccine within 14 days prior to the injection;
• Administration of any subunit vaccine or inactivated vaccine within 7 days prior to the injection;
• Administration of treatment of immunosuppressants (e.g., corticosteroid) within 1 month prior to the injection, or planning for such treatment during this study;
• Body temperature > 37.0 °C before injection;
• Based on the evaluation of the investigator, there was any other factor that indicating the person was unsuitable for this study;

Exclusion Criteria of the Second Injection:

• Any acute infectious disease, body temperature > 38.5 °C or acute attacks of chronic diseases within 3 days prior to the second injection;
• Administration of blood product or other investigational drug during this study;
• Occurrence of adverse event at grade 3 or higher and the event was related to the first injection;
• The investigator or the Ethic Committee decided that the subject should be excluded;