Study on Effectiveness of 2-dose Live Attenuated Varicella Vaccine

Inclusion Criteria: * Aged 1 to 7 * Without a previous history of varicella * With an axillary temperature ≤37.5℃ at the time of vaccination * Appropriate varicella vaccination history * With guardian signing the informed consent and available for clinical observation Exclusion Criteria: * Hypersensitive to any active substance of the vaccine including excipients and antibiotics * With acute illness, severe or acute attack of chronic illness or fever * With immunodeficiency or weakened immune system or being treated with immunosuppressant drugs * Suffering a brain disease, uncontrolled epilepsy or progressive nerve system disease * With a family or personal history of seizure, chronic illness, epilepsy or allergy * With unknown immunization history or unable to follow the immunization schedule of EPI * Received any vaccine within 4 weeks or willing to receive any vaccine in 1 month * With hemorrhagic tendency or prolonged period of bleeding * Received whole blood, plasma or immunoglobulin within 5 months * Received systemic antibiotics or antiviral treatment for acute illness within 7 days * With an axillary temperature ≥38℃ within 3 days * Participating in another clinical trial * Any situation that might influence the consequence of the clinical trial