Effector and Memory Immune Responses to HPV Vaccination in Vietnamese Women Post Virus Exposure

Primary objective: To determine whether antibody geometric mean titer (GMT) to vaccine type HPV16 and HPV18 at 7 months (m) are non-inferior between female sex workers (FSW) aged 18-26 years who received the standard (0, 2m, 6m) and those received the extended 3-dose (at 0, 6m and 18m) 9vHPV schedule and age-matched non-FSW who received an extended 3-dose (at 0, 6m and 18m) 9vHPV schedule. This extended 3-dose schedule is in line with the recommended schedule by the vaccine manufacturer in Vietnam. Secondary objectives: 1. To compare antibody GMT at 2m, 7m, 18m and 19m between FSW who are HPV DNA+/seropositive with FSW who are HPV DNA-/seronegative at baseline. 2. To compare antibody GMT at 18m and 19m between FSW and non-FSW. 3. To determine cellular immune responses to HPV16 and 18 at baseline, 2m, 7m, 18m and 19m. 4. To measure incidence and 6m/12m/18m persistent HPV infection. Primary hypothesis: HPV antibody GMT to HPV16 and 18 in FSW is non-inferior to those of young women of the same age group (non-FSW) at 7m. Secondary hypothesis: 1. HPV antibody GMT are similar at 2m, 7m, 18m and 19m between FSW who are HPV DNA+/seropositive and HPV DNA-/seronegative at month 0. 2. HPV antibody GMT are similar at 18m and 19m between FSW and non-FSW who received the extended schedule. 3. Cellular immune responses to HPV16 and 18 are similar between FSW and non-FSW at 2m, 7m, 18m and 19m who received the extended schedule. 4. No new vaccine-type HPV infection in FSW and non-FSW in all groups at 6m, 12m, 18m.