No. 37 US Department of Health and Human Services/Centers for Disease Control and Prevention FIGURE 1. Observed versus expected percentage of fully vaccinated persons among COVID-19 cases, hospitalizations, and deaths based on population vaccination coverage* and assumed 80%–95% vaccine effectiveness,† by week§ and age group —April 4–June 10 (Delta 50%, using weighted estimates for 13 jurisdictions combined. † To ascertain COVID-19–associated hospitalizations, two jurisdictions relied upon case investigations; seven jurisdictions relied upon hospital records; two jurisdictions relied upon both case investigations and hospital records; and two did not submit hospitalization data. Four jurisdictions reported hospitalizations only where COVID-19 was the cause, and seven reported COVID-19 cases in persons hospitalized for any cause. § To ascertain COVID-19–associated deaths, eight jurisdictions relied upon vital records, and five jurisdictions relied upon a combination of vital records and provider reporting (two), case investigations and vital records (two), and provider reporting, case investigations, and vital records (one). Eleven jurisdictions provided deaths with COVID-19 as a cause; one provided all deaths that occurred within 30 days of becoming a case (without confirming cause); and one provided deaths confirmed with COVID-19 as a cause or within 60 days of positive specimen collection. ¶ Fully vaccinated persons are those who are ≥14 days postcompletion of the primary series of a COVID-19 vaccine with Food and Drug Administration emergency use authorization. Not fully vaccinated persons are those who did not receive a COVID-19 vaccine with Food and Drug Administration emergency use authorization or who received a COVID-19 vaccine but are not yet considered fully vaccinated. ** Alabama, Arizona, Colorado, Indiana, Los Angeles County (California), Louisiana, Maryland, Minnesota, New Mexico, New York City (New York), North Carolina, Seattle/King County (Washington), and Utah. Corresponding author: Heather Scobie, hscobie@cdc.gov. 1Epidemiology Task Force, CDC COVID-19 Response Team; 2Data Analytics and Visualization Task Force, CDC COVID-19 Response Team; 3Colorado Department of Public Health and Environment; 4Acute Communicable Disease Control Program, Los Angeles County Department of Public Health, California; 5New York City Department of Health and Mental Hygiene, New York; 6Maryland Department of Health; 7Arizona Department of Health Services; 8Alabama Department of Health; 9Utah Department of Health; 10Public Health – Seattle & King County, Washington; 11North Carolina Department of Health and Human Services; 12Louisiana Department of Health; 13Indiana State Department of Health; 14Minnesota Department of Health; 15New Mexico Department of Health. All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Janelle Delgadillo reports grant support from the Utah Department of Health. Ruth Lynfield reports that she is president of the Council of State and Territorial Epidemiologists, Secretary of the National Foundation for Infectious Diseases, and Associate Editor of the American Academy of Pediatrics Red Book (the fee for which is donated to the Minnesota Department of Health). Rachel K. Herlihy reports funding from the Council of State and Territorial Epidemiologists for travel to meetings and conferences. No other potential conflicts of interest were disclosed. Summary What is already known about this topic? The incidence of SARS-CoV-2 infection, hospitalization, and death is higher in unvaccinated than vaccinated persons, and the incidence rate ratios are related to vaccine effectiveness. What is added by this report? Across 13 U.S. jurisdictions, incidence rate ratios for hospitalization and death changed relatively little after the SARS-CoV-2 B.1.617.2 (Delta) variant reached predominance, suggesting high, continued vaccine effectiveness against severe COVID-19. Case IRRs decreased, suggesting reduced vaccine effectiveness for prevention of SARS-CoV-2 infections. What are the