(1) Background: Periodic resurgences in COVID-19 due to more contagious variants highlight the need to increase coverage of booster doses. (2) Methods: Our September 2022 nationally representative survey of US adults measured COVID-19 vaccination status, intentions, attitudes, values, and confidence in information sources. (3) Findings: Although 85% of the weighted sample reported receiving at least one dose of a COVID-19 vaccine, only 63% reported being up-to-date on COVID-19 vaccines (e.g., received a booster dose). Only 12% of those not yet up-to-date indicated they were likely to get up-to-date as soon as possible, whereas 42% were unlikely to ever get up-to-date, and 46% were still uncertain. Most of those not up-to-date on their COVID-19 vaccines were under 45 years of age (58%), without a bachelor’s degree (76%), making under $75,000 annually (53%), and Republican or Independent (82%). Prevalent concerns about COVID-19 vaccines among those uncertain about getting up-to-date included: potential side effects that have not been figured out yet (88%), speed of development (77%), newness (75%), ingredients (69%), drug companies making money (67%), allergic reactions (65%), and experimenting on people (63%). (4) Conclusions: Nearly half of adults not yet up-to-date on COVID-19 vaccines were uncertain about doing so, indicating an opportunity to support their decision-making.