Human papillomavirus (HPV) causes the most prevalent sexually transmitted infections in the world. The nonavalent HPV vaccine (9vHPV) provides protection against 9 high-risk HPV serotypes, responsible for causing approximately 90% of cervical and other HPV-related anogenital cancers, as well as 90% of genital warts. The risk of cancer is substantially increased among immunocompromised patients.

Although studies have demonstrated seroprotection among children and adolescents, boys and girls, with the 9vHPV vaccine, the immunogenicity of this vaccine has been poorly explored in immunocompromised children and adolescents (including transplant patients, and those infected with human immunodeficiency virus (HIV)). Several factors, including the immunological consequences of vertically acquired infection, immunosuppressive therapies and age, could lead to an increased risk of infection in children and adolescents who are immunocompromised. Lower immunogenicity in these populations. These children may have a poor response to vaccines and therefore require additional doses. Markers such as CD4/CD8 or torque teno virus (TTV) replication could be linked to immunogenicity and thus serve as predictors of efficacy for routine clinical practice.

Inclusion Criteria:

• Children or adolescents 9 to <18 years of age
• Willing to sign consent/assent form
• If HIV positive, under ART and undetectable viral load and CD4 cell count >200/mm3 (at least 6 months)
• If the patient has received chemotherapy or is a SOT/HSCT recipient, referred for immunizations after adequate immune reconstitution according to routine clinical practice

Exclusion Criteria:

• Previous history of warts and/or anal cancer.
• Previous immunization with any HPV vaccine.
• Age below 9.
• Patients who for any reason should not be included in the study according to the evaluation of the research team.