Second Dose of Varicella Vaccine in Healthy Children

This study aim to assess the immunogenicity and safety of interchangeable administration of the second dose of varicella vaccine. A total of 300 healthy participants aged 15 months - 12 years will be enrolled. Written informed consent form will be obtained from participants' parents or legally acceptable representatives (and assents will be obtained from participants aged above 9 years old and written consent forms will be prepared and consent will be obtained in writing if possible from the participants aged 3-8 years old.) before enrollment. Participants will be assigned to 5 groups according to the brand of first dose varicella vaccine they received at the age of 12 months. All participants will receive the second dose of varicella vaccine manufactured by Sinovac. The duration of individual participation from enrollment to the last onsite visit will be a maximum of 42 days. The end of study is considered the completion of the last visit for the last participant in this study. Blood samples (2.5 - 3.0ml per time) for immunogenicity assessment will be collected. The blood samples will be collected before vaccination and 42 days after vaccination.