6-12 weeks old low dose (3 dose,1 month interval) group:All subjects will receive one dose of Recombinant Trivalent Subunit Rotavirus Vaccine or placebo at Months 0, 1 and 2.

A Phase I Randomized, Double-blind, Placebo-controlled Clinical Trial to Evaluate the Safety and Immunogenicity of Recombinant Trivalent Subunit Rotavirus Vaccine in Healthy Infants Starting at Age 6-12 Weeks and Healthy Subjects aged 7 Months to 49 years old

A Phase II Randomized, Double-blind, Placebo-controlled Clinical Trial to Evaluate the Safety and Immunogenicity of Recombinant Trivalent Subunit Rotavirus Vaccine in Healthy Infants Starting at Age 6-12 Weeks and 7-71 Months