Monitoring Incidence of COVID-19 Cases, Hospitalizations, and Deaths, by Vaccination Status — 13 U.S. Jurisdictions, April 4–July 17, 2021
Heather M. Scobie, Amelia G. Johnson, Amitabh B. Suthar, Rachel Severson, Nisha B. Alden, Sharon Balter, Daniel Bertolino, David Blythe, Shane Brady, Betsy L. Cadwell, Iris Cheng, Sherri Davidson, Janelle Delgadillo, Katelynn Devinney, Jeff Duchin, Monique Duwell, Rebecca Fisher, Aaron T. Fleischauer, Ashley Grant, Jennifer Griffin, Meredith Haddix, Julie Hand, Matt Hanson, Eric J. Hawkins, Rachel Herlihy, Liam Hicks, Corinne Holtzman, Mikhail Hoskins, Judie Hyun, Ramandeep Kaur, Meagan Kay, Holly Kidrowski, Curi Kim, Kenneth Komatsu, Kiersten J. Kugeler, Melissa Lewis, B. Casey Lyons, Shelby Lyons, Ruth Lynfield, Keegan McCaffrey, Chelsea McMullen, Lauren Milroy, Stéphanie Meyer, Leisha D. Nolen, Monita R. Patel, Sargis Pogosjans, Heather E. Reese, Amy Saupe, Jessica Sell, Theresa Sokol, Daniel M. Sosin, Emma Stanislawski, Kelly Stevens, Hailey Vest, Kelly White, Erica Wilson, Adam MacNeil, Matthew D. Ritchey, Benjamin J. Silk
Abstract
COVID-19 vaccine breakthrough infection surveillance helps monitor trends in disease incidence and severe outcomes in fully vaccinated persons, including the impact of the highly transmissible B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19. Reported COVID-19 cases, hospitalizations, and deaths occurring among persons aged ≥18 years during April 4-July 17, 2021, were analyzed by vaccination status across 13 U.S. jurisdictions that routinely linked case surveillance and immunization registry data. Averaged weekly, age-standardized incidence rate ratios (IRRs) for cases among persons who were not fully vaccinated compared with those among fully vaccinated persons decreased from 11.1 (95% confidence interval [CI] = 7.8-15.8) to 4.6 (95% CI = 2.5-8.5) between two periods when prevalence of the Delta variant was lower (<50% of sequenced isolates; April 4-June 19) and higher (≥50%; June 20-July 17), and IRRs for hospitalizations and deaths decreased between the same two periods, from 13.3 (95% CI = 11.3-15.6) to 10.4 (95% CI = 8.1-13.3) and from 16.6 (95% CI = 13.5-20.4) to 11.3 (95% CI = 9.1-13.9). Findings were consistent with a potential decline in vaccine protection against confirmed SARS-CoV-2 infection and continued strong protection against COVID-19-associated hospitalization and death. Getting vaccinated protects against severe illness from COVID-19, including the Delta variant, and monitoring COVID-19 incidence by vaccination status might provide early signals of changes in vaccine-related protection that can be confirmed through well-controlled vaccine effectiveness (VE) studies.