Objectives. To assess the impact of the COVID-19 pandemic on immunization services across the life course. Methods. In this retrospective study, we used Michigan immunization registry data from 2018 through September 2020 to assess the number of vaccine doses administered, number of sites providing immunization services to the Vaccines for Children population, provider location types that administer adult vaccines, and vaccination coverage for children. Results. Of 12 004 384 individual vaccine doses assessed, 48.6%, 15.6%, and 35.8% were administered to children (aged 0–8 years), adolescents (aged 9–18 years), and adults (aged 19–105 years), respectively. Doses administered overall decreased beginning in February 2020, with peak declines observed in April 2020 (63.3%). Overall decreases in adult doses were observed in all settings except obstetrics and gynecology provider offices and pharmacies. Local health departments reported a 66.4% decrease in doses reported. For children, the total number of sites administering pediatric vaccines decreased while childhood vaccination coverage decreased 4.4% overall and 5.8% in Medicaid-enrolled children. Conclusions. The critical challenge is to return to prepandemic levels of vaccine doses administered as well as to catch up individuals for vaccinations missed. (Am J Public Health. Published online ahead of print October 7, 2021: e1–e9. https://doi.org/10.2105/AJPH.2021.306474 )