**HPV Vaccine Reduced Dose Study** This study wants to find out if getting 1 dose of the HPV vaccine works as well as getting 2 or 3 doses. HPV is a virus that can cause different types of cancer. The vaccine helps protect against these cancers by making antibodies, which are proteins that fight viruses. This study will look at how well 1 dose works by checking the blood, lymph nodes (small glands that help your body fight infections), and bone marrow (where blood cells are made) of healthy adults aged 18-45. Participants will have blood samples taken and some will get a tiny needle in their armpit to check a lymph node. They might also have a needle put into their hipbone to get a bone marrow sample. The information from this study could help improve vaccines in the future. **Key Points:** - Participants must be willing to get blood tests, a lymph node test, and possibly a bone marrow test. - The study could involve 1 or 2 vaccine doses, but you may get all 3 later. - You must be healthy and not have had the HPV vaccine before.

Note: The study does not include people with certain health issues or those who have received other vaccines recently.