Waning 2-Dose and 3-Dose Effectiveness of mRNA Vaccines Against COVID-19–Associated Emergency Department and Urgent Care Encounters and Hospitalizations Among Adults During Periods of Delta and Omicron Variant Predominance — VISION Network, 10 States, August 2021–January 2022
Authors: Jill M. Ferdinands, Suchitra Rao, Brian E. Dixon, Patrick K. Mitchell, Malini B. DeSilva, Stephanie A. Irving, Ned Lewis, Karthik Natarajan, Edward Stenehjem, Shaun J. Grannis, Jungmi Han, Charlene McEvoy, Toan C. Ong, Allison L. Naleway, Sarah E. Reese, Peter J. Embi, Kristin Dascomb, Nicola P. Klein, Eric P. Griggs, Deepika Konatham, Anupam B. Kharbanda, Duck-Hye Yang, William F. Fadel, Nancy Grisel, Kristin Goddard, Palak Patel, I-Chia Liao, Rebecca Birch, Nimish R. Valvi, Sue Reynolds, Julie Arndorfer, Ousseny Zerbo, Monica Dickerson, Kempapura Murthy, Jeremiah Williams, Catherine H. Bozio, Lenee Blanton, Jennifer R. Verani, Stephanie J. Schrag, Alexandra F. Dalton, Mehiret H. Wondimu, Ruth Link-Gelles, Eduardo Azziz-Baumgartner, Michelle A. Barron, Manjusha Gaglani, Mark G. Thompson, Bruce Fireman
Journal: MMWR Morbidity and Mortality Weekly Report (2022)

CDC recommends that all persons aged ≥12 years receive a booster dose of COVID-19 mRNA vaccine ≥5 months after completion of a primary mRNA vaccination series and that immunocompromised persons receive a third primary dose.* Waning of vaccine protection after 2 doses of mRNA vaccine has been observed during the period of the SARS-CoV-2 B.1.617.2 (Delta) variant predominance† (1-5), but little is known about durability of protection after 3 doses during periods of Delta or SARS-CoV-2 B.1.1.529 (Omicron) variant predominance. A test-negative case-control study design using data from eight VISION Network sites§ examined vaccine effectiveness (VE) against COVID-19 emergency department/urgent care (ED/UC) visits and hospitalizations among U.S. adults aged ≥18 years at various time points after receipt of a second or third vaccine dose during two periods: Delta variant predominance and Omicron variant predominance (i.e., periods when each variant accounted for ≥50% of sequenced isolates).¶ Persons categorized as having received 3 doses included those who received a third dose in a primary series or a booster dose after a 2 dose primary series (including the reduced-dosage Moderna booster). The VISION Network analyzed 241,204 ED/UC encounters** and 93,408 hospitalizations across 10 states during August 26, 2021-January 22, 2022. VE after receipt of both 2 and 3 doses was lower during the Omicron-predominant than during the Delta-predominant period at all time points evaluated. During both periods, VE after receipt of a third dose was higher than that after a second dose; however, VE waned with increasing time since vaccination. During the Omicron period, VE against ED/UC visits was 87% during the first 2 months after a third dose and decreased to 66% among those vaccinated 4-5 months earlier; VE against hospitalizations was 91% during the first 2 months following a third dose and decreased to 78% ≥4 months after a third dose. For both Delta- and Omicron-predominant periods, VE was generally higher for protection against hospitalizations than against ED/UC visits. All eligible persons should remain up to date with recommended COVID-19 vaccinations to best protect against COVID-19-associated hospitalizations and ED/UC visits.