Add-Vacc is an unblinded cluster-randomised trial (CRT) with two arms: (i) the national HPV vaccination programme (girls aged ~14 years, control arm) and (ii) the national programme plus single-dose male HPV vaccination given to a multi-year cohort of boys (intervention arm). The CRT will be conducted in 26 communities/clusters (13 per arm) in northern Tanzania. Boys aged 14 to 18 years in the intervention arm will receive one dose of the 4-valent HPV vaccine (Gardasil®) that protects against HPV 6, 11, 16, and 18. Population genital HPV prevalence in 18 to 21-year-olds will be compared between intervention clusters (female and male vaccination) and control clusters (female vaccination only) at 3 years after the intervention. Blood sampling for immune responses and adverse event data collection will be performed in a subset of 200 male subjects in selected intervention clusters.

Inclusion Criteria:

• Parents and adult male participants (aged 18 years) must sign an ICF and male participants aged less than 18 years must sign an informed assent form (IAF), indicating that they understand the purpose of and procedures required for the study and are willing to participate in the study and to receive HPV vaccination. If the parent or participant cannot read or write, the procedures must be explained and informed consent/assent must be witnessed by a literate third party who is not involved in the conduct of the study.
• Participants must have been born male, and must be aged 14 to 18 years inclusive at time of vaccination.
• Participants must be living in an intervention community (cluster).
• Participants must be willing and able to comply with the protocol requirements.
• Participants must agree to avoid all non-trial immunisations in the 14 days following vaccination with the trial vaccine, other than emergency vaccinations such as post-exposure rabies or tetanus vaccinations.
• Participants must be healthy as determined by a medical history. A physical examination will be conducted if necessary according to the clinician's judgement.

Exclusion Criteria:

Boys will be excluded from HPV vaccination if:

• They have previously been vaccinated against HPV.
• They have a history of allergy or anaphylaxis to one or more of the HPV vaccine components, to yeast or to latex.
• They are enrolled in another vaccine research study that specifically specifies that they must not participate in a study of another vaccine
• They have been diagnosed with a chronic condition (except HIV, as per the comment above), such as an autoimmune condition, sickle cell disease, degenerative disease, neurologic or genetic disease, among others;
• There are significant conditions or clinically significant findings for which, in the opinion of the investigator, participation would not be in the best interest of the participant (e.g., it would compromise their safety or well-being).