This study aims to assess immunogenicity and safety of nd influence of the delivery system (needle-free injector or syringe with needle) of fractional doses (dose sparing) of two vaccines (Varicella and Hepatitis A vaccines) in children aged 13 to 30 months.

The purpose of this study is to evaluate the immunogenicity, safety and influence of the delivery system (needle-free injector or syringe with needle) of fractional doses (dose sparing) (23,3 and 43,3 PFU - plaque-forming units - of live attenuated OKA strain of Varicella-zoster virus and 100 radioimmunoassay units HAV) of chickenpox and Hepatitis A ( vaccines, intradermally administered, compared with full dose of 103,3 PFU, subcutaneously administered, in 600 primo (first) vaccinated children aged 13 to 30 months selected at random at day care centers in São Paulo. Vaccines will be tested sequentially (Varicella on day 0 and Hepatitis A on day 45). Only 400 children will be randomized again for Hepatitis A vaccine testing, the remaining 200 children will receive the regular dose of Hepatitis A vaccine without further assessment. Doses will be administered using two systems: Disposable Needle-free Syringe Jet Injector (DSJI), compared with the conventional procedure using syringes and needles. Serial blood samples will be blindly analyzed to detect antibody seroconversion. Local and systemic adverse events will be assessed according to definition established by Brighton Collaboration Group, 24 and 72 hours, 7 days, 14 days, 21 days and 45 days after each vaccination, through clinical evaluation and telephone calls.

Inclusion Criteria:

• Children of both genders older than 13 months and younger than 30 months of age.
• Available for follow-up for at least 45 days at public day care centers funded by São Paulo City local government.
• Written informed consent signed by parents or legal guardians after reading and explanation

Exclusion Criteria:

• Suspect/verified diagnosis of congenital or acquired immunodeficiency syndrome (AIDS)
• Suspect/verified diagnosis of malign neoplasia
• Children on treatment with high-dose systemic corticosteroids (equivalent to prednisone 2 mg/kg/day, for two or more weeks), or immunosuppressive therapy.
• Received a vaccine with live attenuated strain of virus within less than 30 days
• Suspect/verified diagnosis of chickenpox or has already been immunized against chickenpox (varicella).
• Suspect/verified diagnosis of hypersensibility to any ingredient of the vaccine.
• One of the parents or legal guardians of the minor does not agree with the study.
• Any other circumstances that may potentially damage the minor or prevent procedures from being carried out according to evaluation of the research team.
• Child shows signs or symptoms of an active intercurrent disease (e.g. fever, rash, etc.) that may interfere with the evaluation of adverse events after immunization at the research team's discretion. In this case, the participant may be reevaluated within the following three months in order to verify eligibility.