The purpose of this study is to determine sustained immunogenicity of the quadrivalent vaccine 'Gardasil', 48 months after initial vaccination, among HIV-1 infected boys and girls age 9-14 years. This age range is within the World Health Organization (WHO) stipulated guidelines for national programs for the vaccine.

HIV-infected individuals bear a disproportionate disease burden of HPV-related diseases suggesting more rapid progression from HPV acquisition to malignancy. HIV infected women have a 2-22 fold increased risk for cervical cancer compared to uninfected women. The quadrivalent HPV vaccine marketed as "Gardasil" has demonstrated efficacy against type specific HPV infections known to cause 70% cervical cancer (HPV 16 & 18) and HPV 6 & 11 known to cause 90% of anogenital warts in populations of HIV negative young women.

Since the risk of HPV exposure persists throughout a person's sexual life, the duration of protection, especially when the vaccine is given in the pre-adolescent period, is critical to overall vaccine effectiveness. Extended follow up of HIV-uninfected individuals has shown sustained response to HPV vaccine for 8.4 and 6 years respectively to the bivalent and quadrivalent vaccines. However, other vaccines such as the hepatitis B vaccine have been shown to require additional dosages to be effective among HIV-infected persons.

Data on immunogenicity of the HPV vaccine among HIV infected adolescents is limited to a 12 month follow up period.

Current HPV vaccine guidelines target pre-sexual adolescents. Since the risk of HPV exposure persists throughout an individual's sexual life, the duration of protection provided by vaccination is critical to the overall vaccine effectiveness. Duration of sustained HPV 6/11/16/18 antibody response is directly related to vaccine effectiveness and determines the need for booster dosing.

The investigators therefore propose to extend follow up of 179 girls and boys in Kenya, age 9-14 years who have received 3 doses of the quadrivalent 'Gardasil' vaccine and assess for immunogenicity annually.

Study Location: Partners in Prevention, Thika site

Inclusion Criteria:

• HIV-infected
• age 9-14 years
• guardian/parental consent

Exclusion Criteria:

Participants will be excluded if they

• are severely ill as defined by Karnofsky <70
• have a diagnosis of malignancy
• on-going febrile illness (temperature ≥37.8°C), including active treatment for an opportunistic infection
• have received systemic corticosteroids within prior one year
• have received inactivated vaccine within prior 2 weeks, or live attenuated vaccine within prior 6 weeks
• have history of allergy to any products included in the HPV vaccine
• have received any of blood derivatives within prior 6 months
• are pregnant
• lack parental consent and/or parent declines to provide assent

Study participants will be enrolled from the paediatric HIV-care clinic