The purpose of this study is to evaluate the immunogenicity and safety of a live attenuated mumps vaccine in healthy infants between 8 - 18 months old with a commercialized live attenuated mumps vaccine as the control vaccine.

This study is a randomized, blind, single-center, controlled phase III clinical trial. The purpose of this study is to evaluate the immunogenicity and safety of a live attenuated mumps vaccine manufactured by Sinovac (Dalian) Vaccine Technology Co., Ltd. The control vaccine is a commercialized live attenuated mumps vaccine manufactured by Zhejiang VACN bio-pharmaceutical Co. Ltd. All participants are healthy infants between 8 - 18 months old, and will be randomly assigned into experimental group or control group in the ratio 1:1.

Inclusion Criteria:

• Healthy volunteer between 8 - 18 months old;
• Proven legal identity;
• Guardian(s) of the volunteer should be capable of understanding the written consent form, and such form should be signed before the infant being included into this study;
• Complying with the requirement of the study protocol;

Exclusion Criteria:

• Axillaty temperature > 37.0 °C;

• Any significant abnormity of heart, lung, liver, spleen, lymph nodes, or pharynx;

• Acute disease or acute stage of chronic disease within 7 days prior to study entry;

• Prior vaccination with mumps vaccine or with history of mumps infection;

• History of allergy to any vaccine or vaccine ingredient, or serious adverse reaction(s) about vaccination, such as urticaria, difficulty in breathing, angioneurotic edema, abdominal pain, etc;

• Receipt of any of the following products:

  1. Any subunit vaccine or inactivated vaccine within 14 days prior to study entry;
  2. Any live attenuated vaccine within 28 days prior to study entry;
  3. Any other investigational medicine(s) within 30 days prior to study entry;
  4. Blood product (e.g., immunoglobulin) within 3 months prior to study entry;
  5. Any immunosuppressant, cytotoxic medicine, or inhaled corticosteroids (except corticosteroid spray for treatment of allergic rhinitis or corticosteroid treatment on surface for acute non-complicated dermatitis) within 6 month prior to study entry;

• Epilepsy (except febrile seizures), history of seizures or convulsions, or a family history of mental illness;

• Autoimmune disease or immunodeficiency;

• Congenital malformation, developmental disorders, or serious chronic diseases (such as Down's syndrome, diabetes, sickle cell anemia or neurological disorders;

• Severe malnutrition;

• Diagnosed coagulation function abnormal (e.g., coagulation factor deficiency, coagulation disorder, or platelet abnormalities);

• Any other factor that suggesting the volunteer is unsuitable for this study based on the opinions of investigators;

• Participants with the following conditions between day 0 - 28 of this study would be included in the full analysis set (FAS), but would be excluded from the per protocol set (PPS):

  1. Receipt of any other investigational or unregistered product (drug or vaccine);
  2. Receipt of immunosuppressant (corticosteroid dosage that equivalent to or above 0.5 mg prednisone/kg weight/day) for > 14 days consecutively, except for inhalant or locally administrated corticosteroid;
  3. Receipt of immunoglobulin and/or blood product;
  4. Newly diagnosed autoimmune disease or immunodeficiency (e.g., HIV infection);