This is a follow-up study which is based on the bridging study of a recombinant human papillomavirus 16/18 bivalent vaccine in preadolescent girls(Unique Protocol ID:HPV-PRO-006,Identifiers: NCT02562508) .We will recruit people who have participated in bridging study before and collect their serum samples to test the seroprevalence and geometric mean concentrations of anti-HPV16 and anti-HPV18 antibody on 18 and 30 months after dose 1.