This study investigates the use of an investigational vaccine combined with an immune therapy to treat patients with head and neck cancer linked to the human papilloma virus (HPV). Head and neck cancer can occur in areas such as the throat, mouth, and nose, and when linked to HPV, it is often more challenging to treat. This study aims to understand how effective and safe the combination treatment is for patients whose cancer has returned or spread.

Participants in the study will receive either the investigational vaccine combined with an immune therapy or a placebo. A placebo is an inactive substance that looks like the investigational medicine but does not contain any medicine. The study will involve monitoring the participants' health and response to the treatment to gather data on its safety and effectiveness.

• Who can participate: Adults with head and neck squamous cell carcinoma associated with HPV can participate if their cancer has returned or spread after treatment. Participants must have been treated with a platinum-containing regimen and lack curative treatment options. HPV confirmation by p16 IHC or HPV-16/18 nucleic acid testing is required.
• Study details: Participants will receive either the investigational vaccine and immune therapy or a placebo. A placebo is an inactive substance that looks like the investigational medicine but does not contain any medicine.