Sinovac Biotech Co. Ltd.

The trial aims to assess the tolerability, safety, and immunogenicity of the tetravalent inactivated enterovirus vaccine in adults and children aged 6 months to 12 years. The main questions it aims to answer are:
* Phase Ⅰ: The safety of the investigational vaccine in the target population based on adverse events (AEs);
* Phase Ⅱ: The immunogenicity of the investigational vaccine in the target population.
In Phase I, researchers will compare the safety of the investigational vaccine at low, medium, and high doses with the control vaccine; in Phase II, they will compare the safety and immunogenicity (including immune persistence) of the investigational vaccine at medium and high doses with the control vaccine.
Procedure:
* In Phase I, will be vaccinated with the investigational vaccine (at low, medium, and high doses) or the control EV71 vaccine/placebo in a 3:1 ratio, following a vaccination schedule of 0 and 1 month. Within each age group, and under the premise of ensuring safety, a dose-escalation trial will be conducted in reverse order of age.
* In Phase II, participants in each age group will be randomly assigned to the medium-dose, high-dose investigational vaccine groups, and the control group in a 1:1:1 ratio, receiving two doses of the investigational vaccine or the EV71 vaccine (for ages 6-71 months)/placebo (for ages 6-12 years), with a one-month interval between the two doses.
* For all participants in both Phase I and Phase II, immediate reactions within 30 minutes after each dose will be observed. Diary cards/contact cards will be used to collect solicited local and systemic adverse events (AEs) for 0-7 days and unsolicited AEs for 0-30 days after vaccination. Additionally, serious adverse events (SAEs) will be monitored from the start of vaccination until 6 months post-completion of the vaccination schedule. Furthermore, for participants of reproductive age in Phase I, pregnancy events will be collected.

This multicenter, randomized, double-blind, controlled Phase III clinical trial aims to evaluate the efficacy, safety, and immunogenicity of the bivalent enterovirus-inactivated vaccine (Vero cell) in healthy children aged 6 to 71 months.
The main questions it aims to answer are:
* The primary vaccine efficacy of the investigational vaccine against Hand, Foot, and Mouth Disease（HFMD) caused by CA16 infection compared to the control vaccine.
* The neutralizing antibody levels against EV71 in the trial group are non-inferior to those in the control group after two doses of vaccination.
Researchers will compare the bivalent enterovirus-inactivated vaccine (Vero cell) to the EV71-inactivated vaccine (Vero cell) to prevent HFMD and Herpangina(HA).
Participants will be randomly assigned to the trial group and the control group in a 1:1 ratio to receive two doses of the investigational vaccine or the control EV71 vaccine, with a one-month interval between doses.

This is an Open-labeled, Randomized, Controlled Phase IV Clinical Trial to Evaluate the Immunogenicity and Safety of Booster Dose of Sabin Strain Inactivated Poliovirus Vaccine (Vero cell) (sIPV) Co-administered with Measles, Mumps, Rubella (MMR) Combined Live Attenuated Vaccine and Inactivated Hepatitis A (Hep-A) Vaccine.