Interim Effectiveness of Updated 20232024 (Monovalent XBB.1.5) COVID-19 Vaccines Against COVID-19Associated … – CDC

Jennifer DeCuir, MD, PhD1; Amanda B. Payne, PhD1; Wesley H. Self, MD2; Elizabeth A.K. Rowley, DrPH3; Kristin Dascomb, MD, PhD4; Malini B. DeSilva, MD5; Stephanie A. Irving, MHS6; Shaun J. Grannis, MD7,8; Toan C. Ong, PhD9; Nicola P. Klein, MD, PhD10; Zachary A. Weber, PhD3; Sarah E. Reese, PhD3; Sarah W. Ball, ScD3; Michelle A. Barron9; Allison L. Naleway, PhD6; Brian E. Dixon, PhD7,8; Inih Essien, OD5; Daniel Bride, MS4; Karthik Natarajan, PhD11,12; Bruce Fireman10; Ami B. Shah, MPH1,13; Erica Okwuazi, MSc1,13; Ryan Wiegand, PhD1; Yuwei Zhu, MD2; Adam S. Lauring, MD, PhD14; Emily T. Martin, PhD14; Manjusha Gaglani, MBBS15,16; Ithan D. Peltan, MD17,18; Samuel M. Brown, MD17,18; Adit A. Ginde, MD9; Nicholas M. Mohr, MD19; Kevin W. Gibbs, MD20; David N. Hager, MD, PhD21; Matthew Prekker, MD22; Amira Mohamed, MD23; Vasisht Srinivasan, MD24; Jay S. Steingrub, MD25; Akram Khan, MD26; Laurence W. Busse, MD27; Abhijit Duggal, MD28; Jennifer G. Wilson, MD29; Steven Y. Chang, MD, PhD30; Christopher Mallow, MD31; Jennie H. Kwon, DO32; Matthew C. Exline, MD33; Cristie Columbus, MD15,34; Ivana A. Vaughn, PhD35; Basmah Safdar, MD36; Jarrod M. Mosier, MD37; Estelle S. Harris, MD18; Jonathan D. Casey, MD2; James D. Chappell, MD, PhD2; Carlos G. Grijalva, MD2; Sydney A. Swan2; Cassandra Johnson, MS2; Nathaniel M. Lewis, PhD38; Sascha Ellington, PhD38; Katherine Adams, MPH38; Mark W. Tenforde, MD, PhD38; Clinton R. Paden, PhD1; Fatimah S. Dawood, MD1; Katherine E. Fleming-Dutra, MD1; Diya Surie, MD1; Ruth Link-Gelles, PhD1; CDC COVID-19 Vaccine Effectiveness Collaborators (View author affiliations)

What is already known about this topic?

In September 2023, CDCs Advisory Committee on Immunization Practices recommended updated 20232024 (monovalent XBB.1.5) COVID-19 vaccination for all persons aged 6 months to prevent COVID-19, including severe disease. Few estimates of updated 20232024 vaccine effectiveness against medically attended COVID-19 are available.

What is added by this report?

Receipt of an updated COVID-19 vaccine dose provided increased protection against COVID-19associated emergency department and urgent care encounters and hospitalization compared with no receipt of an updated vaccine dose among immunocompetent U.S. adults during a period of multiple cocirculating SARS-CoV-2 Omicron lineages.

What are the implications for public health practice?

These findings support CDC recommendations for updated 20232024 COVID-19 vaccination. All persons aged 6 months should receive updated 20232024 COVID-19 vaccine.

In September 2023, CDCs Advisory Committee on Immunization Practices recommended updated 20232024 (monovalent XBB.1.5) COVID-19 vaccination for all persons aged 6 months to prevent COVID-19, including severe disease. However, few estimates of updated vaccine effectiveness (VE) against medically attended illness are available. This analysis evaluated VE of an updated COVID-19 vaccine dose against COVID-19associated emergency department (ED) or urgent care (UC) encounters and hospitalization among immunocompetent adults aged 18 years during September 2023January 2024 using a test-negative, case-control design with data from two CDC VE networks. VE against COVID-19associated ED/UC encounters was 51% (95% CI = 47%54%) during the first 759 days after an updated dose and 39% (95% CI = 33%45%) during the 60119 days after an updated dose. VE estimates against COVID-19associated hospitalization from two CDC VE networks were 52% (95% CI = 47%57%) and 43% (95% CI = 27%56%), with a median interval from updated dose of 42 and 47 days, respectively. Updated COVID-19 vaccine provided increased protection against COVID-19associated ED/UC encounters and hospitalization among immunocompetent adults. These results support CDC recommendations for updated 20232024 COVID-19 vaccination. All persons aged 6 months should receive updated 20232024 COVID-19 vaccine.

On September 12, 2023, CDCs Advisory Committee on Immunization Practices recommended updated 20232024 COVID-19 vaccination with a monovalent XBB.1.5derived vaccine for all persons aged 6 months to prevent COVID-19, including severe disease (1). Although 1 updated vaccine dose is recommended for most persons aged 5 years, vaccination coverage with updated vaccines has remained low,* including among those at highest risk for severe disease, such as adults aged 65 years. Thousands of persons in the United States continue to be hospitalized with COVID-19 each week, including approximately 31,000 during January 713, 2024, despite endemicity and increased population immunity to SARS-CoV-2. This analysis estimated updated COVID-19 vaccine effectiveness (VE) during September 2023January 2024 among immunocompetent adults aged 18 years against COVID-19associated emergency department (ED) or urgent care (UC) encounters in one CDC VE network and VE against COVID-19associated hospitalization in two CDC VE networks.

Methods for Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network (VISION) and Investigating Respiratory Viruses in the Acutely Ill (IVY) VE analyses have been described (2,3). VISION is a multisite, electronic health records (EHR)based network including 369 EDs and UCs and 229 hospitals in eight states that uses a test-negative, case-control design to estimate COVID-19 VE. Eligible patients must receive molecular testing (e.g., real-time reverse transcriptionpolymerase chain reaction [RT-PCR] testing) for SARS-CoV-2 during the 10 days preceding or up to 72 hours after a COVID-19associated ED/UC encounter or hospital admission.** COVID-19 vaccination history is ascertained from state or jurisdictional registries, EHRs, and, in a subset of sites, medical claims data.

IVY is a multisite, inpatient network including 26 hospitals in 20 U.S. states that uses a test-negative, case-control design to prospectively enroll patients with COVID-19like illness (CLI) who receive testing for SARS-CoV-2 within 10 days of illness onset and 3 days of hospital admission. Nasal swabs are collected for central RT-PCR testing for SARS-CoV-2 at Vanderbilt University Medical Center (Nashville, Tennessee), and SARS-CoV-2positive specimens are sent to the University of Michigan (Ann Arbor, Michigan) for whole genome sequencing to identify SARS-CoV-2 lineages. Demographic and clinical data are collected through EHR review and patient or proxy interview. COVID-19 vaccination history is ascertained from state or jurisdictional registries, EHRs, and self-report.

The VISION and IVY networks conducted separate VE analyses. In both analyses, immunocompetent adults aged 18 years who 1) had a medical encounter at an ED/UC (VISION only) or 2) were hospitalized (VISION and IVY) at a participating facility with CLI were included. Case-patients were those who received a positive SARS-CoV-2 molecular test result, and control patients were those who received a negative SARS-CoV-2 test result. Participants were excluded if they 1) received a COVID-19 vaccine dose <7 days before their eligible ED/UC encounter or hospitalization; 2) received an updated COVID-19 vaccine dose <2 months after receiving a previous COVID-19 vaccine dose (to align with current Advisory Committee on Immunization Practices recommendations); 3) received a bivalent COVID-19 vaccine dose after September 10, 2023; 4) received an updated COVID-19 vaccine dose before September 13, 2023; or 5) received >1 updated COVID-19 vaccine dose.*** Case-patients were also excluded if they had received a positive influenza or respiratory syncytial virus (RSV) molecular test result at the time of their CLI encounter. Because of potential confounding caused by the association between COVID-19 and influenza vaccination behaviors, control patients who received positive or indeterminant influenza test results were excluded from the primary analysis (4). A sensitivity analysis including these control patients was also conducted.

Odds ratios (ORs) and 95% CIs were estimated using multivariable logistic regression comparing persons who received an updated COVID-19 vaccine dose with those who did not, irrespective of the number of previous original or bivalent COVID-19 vaccine doses received (if any), among case-patients and control patients. VE models were adjusted for age, sex, race and ethnicity, calendar time, and geographic region. VE was calculated as (1 adjusted OR) 100%. In the VISION network, VE was estimated for adults aged 18 years and by age group (1864 and 65 years). In the IVY network, statistical power was limited among younger adults because of lower vaccination coverage and fewer COVID-19associated hospitalizations among persons aged 1864 years; therefore, VE against hospitalization was estimated only for adults aged 18 years and 65 years.

Analyses were conducted using R software (version 4.3.2; R Foundation) for the VISION analysis and SAS software (version 9.4; SAS Institute) for the IVY analysis. This activity was reviewed by CDC, deemed not research, and was conducted consistent with applicable federal law and CDC policy.**** This activity was reviewed and approved as a research activity by one VISION site.

Among adults aged 18 years in the VISION network, 128,825 ED/UC encounters met inclusion criteria, including 17,229 case-patients and 111,596 control patients (Table 1). A total of 1,297 (8%) case-patients and 13,378 (12%) control patients had received an updated COVID-19 vaccine dose. VE against COVID-19associated ED/UC encounters was 51% (95% CI = 47%54%) in the first 759 days after an updated dose (median interval since updated dose = 33 days) and 39% (95% CI = 33%45%) in the 60119 days after an updated dose (median interval since updated dose = 74 days) (Table 2). Among adults aged 18-64 years, VE against COVID-19associated ED/UC encounters was 52% (95% CI = 45%58%) in the first 759 days after an updated dose (median interval since updated dose = 31 days) and 45% (95% CI = 34%55%) in the 60119 days after an updated dose (median interval since updated dose = 73 days). Among adults aged 65 years, VE against COVID-19associated ED/UC encounters was 49% (95% CI = 44%54%) in the first 759 days after an updated dose (median interval since updated dose = 33 days) and 37% (95% CI = 29%44%) in the 60119 days after an updated dose (median interval since updated dose = 74 days).

VISION network. Among adults aged 18 years in the VISION network, 37,503 hospitalizations met criteria for inclusion in analyses, including 4,589 case-patients and 32,914 control patients (Table 3). A total of 395 (9%) case-patients and 4,199 (13%) control patients had received an updated COVID-19 vaccine dose. VE against COVID-19associated hospitalization was 53% (95% CI = 46%59%) in the first 759 days after an updated dose (median interval since updated dose = 32 days) and 50% (95% CI = 40%59%) in the 60119 days after an updated dose (median interval since updated dose = 73 days). Among patients aged 65 years, VE against COVID-19associated hospitalization was 54% (95% CI = 47%60%) in the first 759 days after an updated dose (median interval since updated dose = 32 days) and 50% (95% CI = 39%59%) in the 60119 days after an updated dose (median interval since updated dose = 73 days).

IVY network. Among adults aged 18 years in the IVY network, 4,117 met criteria for inclusion in analyses, including 1,194 case-patients and 2,923 control patients. A total of 94 (8%) case-patients and 353 (12%) control patients had received an updated COVID-19 vaccine dose. VE of an updated dose against COVID-19associated hospitalization was 43% (95% CI = 27%56%, median interval since updated dose = 47 days) among adults aged 18 years and 48% (95% CI = 31%61%, median interval since updated dose = 48 days) among adults aged 65 years.

Including control patients who received positive or indeterminant influenza test results added 1,819 control patients to the VISION hospitalization analysis and including control patients who received positive or indeterminant influenza test results or had missing influenza test results added 511 control patients to the IVY hospitalization analysis (Supplementary Table 1, https://stacks.cdc.gov/view/cdc/148434). VE estimates in supplementary analyses including control patients who received positive or indeterminant influenza test results did not differ meaningfully from those in the main analyses for ED/UC encounters (Supplementary Table 2, https://stacks.cdc.gov/view/cdc/148435) or hospitalization (Supplementary Table 3, https://stacks.cdc.gov/view/cdc/148436).

Whole genome sequencing data were available for SARS-CoV-2positive specimens collected in the IVY network during September 21December 15, 2023. Among 952 sequenced specimens, 154 (16%) had XBB.1.5like spike proteins, 550 (58%) had EG.5like spike proteins with an F456L substitution compared with XBB.1.5, 189 (20%) had HK.3like spike proteins with L455F and F456L substitutions compared with XBB.1.5, 57 (6%) had JN.1like spike proteins with more than30 substitutions compared with XBB.1.5, and two (<1%) had other spike proteins. Similarly, among 18,316 SARS-CoV-2positive specimens collected during the same period and sequenced by CDC as part of national genomic surveillance, 2,624 (14%) had XBB.1.5like spike proteins, 9,649 (53%) had EG.5like spike proteins, 3,700 (20%) had HK.3like spike proteins, 2,302 (13%) had JN.1like spike proteins, and 41 (<1%) had other spike proteins.

During September 2023January 2024, in two multisite VE networks, updated 20232024 COVID-19 vaccination provided significant protection against COVID-19associated ED/UC encounters and hospitalization among immunocompetent adults, compared with not receiving an updated vaccine. The comparison group included both unvaccinated persons and persons who had received original monovalent or bivalent doses only; thus, these results support current CDC recommendations for updated COVID-19 vaccination, including among persons who have previously received original monovalent or bivalent COVID-19 vaccines and those who have never been vaccinated, irrespective of previous infection history (1).

Updated COVID-19 vaccines contain the spike antigen from the SARS-CoV-2 Omicron XBB.1.5 virus, which was the predominant variant circulating in the United States during the first half of 2023. Many other XBB lineages cocirculated during fall 2023 that had amino acid substitutions associated with increased escape from neutralizing antibodies, such as EG.5 and HK.3 (5). The JN.1 lineage, a descendent of Omicron BA.2.86, was first detected in the United States in September 2023 and accounted for approximately 65% of circulating lineages by the 2-week period ending January 6, 2024.***** As noted, JN.1 contains more than 30 substitutions in the spike protein compared with XBB.1.5, some of which might be associated with immune escape (5). Although studies have found that updated COVID-19 vaccines elicit broadly cross-protective neutralizing antibodies, including against XBB lineages and JN.1 (57), the pace and frequency with which new SARS-CoV-2 lineages have displaced predecessors underscores the need for ongoing monitoring of COVID-19 VE and for periodic COVID-19 vaccine antigen updates. These analyses include periods when XBB lineages and JN.1 cocirculated to varying degrees in the United States, indicating that receipt of updated vaccines provided protection against COVID-19associated ED/UC encounters and hospitalization due to the variants cocirculating during this period.

Despite different populations, methods, and outcomes, estimates of the effectiveness of updated COVID-19 vaccines were aligned across the VISION and IVY analyses. VE estimates were also similar to those recently published from another CDC VE platform, which measured VE against symptomatic SARS-CoV-2 infection (8), and to a United Kingdom report, which measured VE against hospitalization among patients aged 65 years. Earlier estimates of the effectiveness of updated COVID-19 vaccines against hospitalization in older adults from Denmark (9) and the Netherlands (10) were somewhat higher than those observed in this analysis; however, this is likely due to a shorter interval since updated dose receipt among patients included in the European studies or to differences in study methods. Whereas the maximum interval since receipt of an updated dose was 25 days in the Danish report and 2 months in the Dutch report, persons in the VISION and IVY analyses could have received an updated dose up to 4 months earlier.

In the VISION analysis, there was evidence of waning effectiveness of updated COVID-19 vaccines against ED/UC encounters; however, COVID-19associated hospitalization rates during the analysis period were relatively low compared with previous years, limiting the evaluation of waning VE against hospitalization and precluding estimation of VE against critical illness. Analyses from VISION and IVY during 20222023 showed substantial waning of COVID-19 VE against ED/UC encounters and hospitalization, with VE not significantly different from zero in some strata by 6 months after vaccination, although VE was more sustained against critical illness (2,3) (defined as receipt of invasive mechanical ventilation, intensive care unit admission, or death), with protection lasting well over 1 year after the most recent dose. Continued monitoring of the effectiveness of updated COVID-19 vaccines for expected waning against hospitalization and to determine the durability of VE against critical illness is needed.

The findings in this report are subject to at least five limitations. First, although case-patients were required to meet a CLI definition and to receive a positive SARS-CoV-2 test result, they might have visited EDs or UCs or been hospitalized for reasons other than COVID-19, which could have lowered VE estimates. Second, misclassification of vaccination status was possible, because state registries, EHRs, medical claims data, and self-report might not identify all updated COVID-19 vaccine doses administered, which would likely result in underestimation of VE. Third, analyses did not account for previous SARS-CoV-2 infection, which might provide protection against future COVID-19. VE should therefore be interpreted as the incremental benefit of an updated dose in a population with high levels of infection-induced immunity, vaccine-induced immunity, or both. Fourth, although analyses were adjusted for relevant confounders, residual confounding from other factors, including behavioral modifications to prevent SARS-CoV-2 exposure and outpatient antiviral treatment for COVID-19, is possible. Finally, sample size limitations precluded estimation of lineage-specific VE and stratification of VE by interval since updated dose receipt in the IVY analysis.

In this analysis of the effectiveness of updated COVID-19 vaccines, receipt of an updated COVID-19 vaccine dose provided protection against COVID-19associated ED/UC encounters and hospitalization among immunocompetent adults. CDC will continue monitoring VE of updated COVID-19 vaccines. These results support CDC recommendations for updated 20232024 COVID-19 vaccination. All persons aged 6 months should receive updated 20232024 COVID-19 vaccine.

Monica Dickerson, Abby L. Martin, Ralph D. Whitehead, Jr., CDC; Marcia A. Blair, Shanice L. Cummings, Rendie E. McHenry, Laura Short, Vanderbilt University Medical Center.

Shekhar Ghamande; Robert Gottlieb; Tresa McNeal; Catherine Raver; William Bender; Linda Fletcher; Phillip Heaton; Sheryl Kane; Charlene McEvoy; Sunita Thapa; Gabriela Vazquez-Benitez; Anne Frosch; Lois E Lamerato; Mayur Ramesh; Julie Arnofer; Harith Ali; Johns Hopkins; Bradley Crane; Padma Dandamudi; Kristin Goddard; John Hansen; Julius Timbol; Ousseny Zerbo; Katie Allen; Thomas Duszynski; William Fadel; Colin Rogerson; Nida Qadir; Catia Chavez; Bryant Doyle; David Mayer; Suchitra Rao; Carolina Rivas; Nicholas J. Johnson; Adrienne Baughman; Cara T. Lwin; Jillian P. Rhoads; Kelsey N. Womack; Margaret Dunne; Allison Ciesla; Josephine Mak; Morgan Najdowski; Caitlin Ray

1Coronavirus and Other Respiratory Viruses Division, National Center for Immunization and Respiratory Diseases, CDC; 2Vanderbilt University Medical Center, Nashville, Tennessee; 3Westat, Rockville, Maryland; 4Division of Infectious Diseases and Clinical Epidemiology, Intermountain Healthcare, Salt Lake City, Utah; 5HealthPartners Institute, Minneapolis, Minnesota; 6Kaiser Permanente Center for Health Research, Portland, Oregon; 7Indiana University School of Medicine, Indianapolis, Indiana; 8Regenstrief Institute Center for Biomedical Informatics, Indianapolis, Indiana; 9University of Colorado School of Medicine, Aurora, Colorado; 10Kaiser Permanente Vaccine Study Center, Kaiser Permanente Northern California Division of Research, Oakland, California; 11Department of Biomedical Informatics, Columbia University Irving Medical Center, New York, New York; 12New York-Presbyterian Hospital, New York, New York; 13General Dynamics Information Technology, Falls Church, Virginia; 14University of Michigan, Ann Arbor, Michigan; 15Baylor Scott & White Health, Texas; 16Baylor College of Medicine, Temple, Texas; 17Intermountain Medical Center, Murray, Utah; 18University of Utah, Salt Lake City, Utah; 19University of Iowa, Iowa City, Iowa; 20Wake Forest School of Medicine, Winston-Salem, North Carolina; 21Johns Hopkins University School of Medicine, Baltimore, Maryland; 22Hennepin County Medical Center, Minneapolis, Minnesota; 23Montefiore Medical Center, Albert Einstein College of Medicine, New York, New York; 24University of Washington, Seattle, Washington; 25Baystate Medical Center, Springfield, Massachusetts; 26Oregon Health & Science University, Portland, Oregon; 27Emory University, Atlanta, Georgia; 28Cleveland Clinic, Cleveland, Ohio; 29Stanford University School of Medicine, Stanford, California; 30Ronald Reagan UCLA Medical Center, Los Angeles, California; 31University of Miami, Miami, Florida; 32Washington University in St. Louis, St. Louis, Missouri; 33The Ohio State University, Columbus, Ohio; 34Texas A&M University College of Medicine, Dallas, Texas; 35Henry Ford Health, Detroit, Michigan; 36Yale University School of Medicine, New Haven, Connecticut; 37University of Arizona, Tucson, Arizona; 38Influenza Division, National Center for Immunization and Respiratory Diseases, CDC.

Abbreviations: ED=emergency department; HHS=U.S. Department of Health and Human Services; IVY=Investigating Respiratory Viruses in the Acutely Ill; NH=non-Hispanic; UC=urgent care; VE = vaccine effectiveness; VISION=Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network. * The no updated dose group included all eligible persons who did not receive an updated 20232024 COVID-19 vaccine dose, regardless of number of previous (i.e., original monovalent and bivalent) doses (if any) received. For VISION, Other, NH race includes persons reporting NH ethnicity and any of the following for race: American Indian or Alaska Native, Asian, Native Hawaiian or other Pacific Islander, other races not listed, and multiple races; because of small numbers, these categories were combined. For IVY, Other, NH race includes Asian, Native American or Alaska Native, and Native Hawaiian or other Pacific Islander; because of small numbers, these categories were combined. For VISION, Unknown includes persons with missing race and ethnicity in their electronic health records. For IVY, Unknown includes patients who self-reported their race and ethnicity as Other and those for whom race and ethnicity were unknown. Regions are defined by HHS. States included in each region are available at https://www.hhs.gov/about/agencies/iea/regional-offices/index.html. VISION network sites included were located as follows. Region 5: HealthPartners (Minnesota and Wisconsin) and Regenstrief Institute (Indiana); Region 8: Intermountain Healthcare (Utah) and University of Colorado (Colorado); Region 9: Kaiser Permanente Northern California (California); and Region 10: Kaiser Permanente Northwest (Oregon and Washington). IVY network sites were located as follows: Region 1: Baystate Medical Center (Springfield, Massachusetts), Beth Israel Deaconess Medical Center (Boston, Massachusetts), and Yale University (New Haven, Connecticut); Region 2: Montefiore Medical Center (New York, New York); Region 3: Johns Hopkins Hospital (Baltimore, Maryland); Region 4: Emory University Medical Center (Atlanta, Georgia), University of Miami Medical Center (Miami, Florida), Vanderbilt University Medical Center (Nashville, Tennessee), and Wake Forest University Baptist Medical Center (Winston-Salem, North Carolina); Region 5: Cleveland Clinic (Cleveland, Ohio), Hennepin County Medical Center (Minneapolis, Minnesota), Henry Ford Health (Detroit, Michigan), The Ohio State University Wexner Medical Center (Columbus, Ohio), and University of Michigan Hospital (Ann Arbor, Michigan); Region 6: Baylor Scott & White Medical Center (Temple, Texas) and Baylor University Medical Center (Dallas, Texas); Region 7: Barnes-Jewish Hospital (St. Louis, Missouri) and University of Iowa Hospitals (Iowa City, Iowa); Region 8: Intermountain Medical Center (Murray, Utah), UCHealth University of Colorado Hospital (Aurora, Colorado), and University of Utah (Salt Lake City, Utah); Region 9: Stanford University Medical Center (Stanford, California), Ronald Reagan UCLA Medical Center (Los Angeles, California), and University of Arizona Medical Center (Tucson, Arizona); and Region 10: Oregon Health & Science University Hospital (Portland, Oregon) and University of Washington (Seattle, Washington). ** VISION underlying condition categories included pulmonary, cardiovascular, cerebrovascular, musculoskeletal, neurologic, hematologic, endocrine, renal, and gastrointestinal. IVY underlying condition categories included pulmonary, cardiovascular, neurologic, hematologic, endocrine, renal, gastrointestinal, and autoimmune. The JN.1 predominant period was considered to have started December 24, 2023.

Abbreviations: Ref=referent group; VE=vaccine effectiveness; VISION=Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network. * VE was calculated as (1 odds ratio) 100% with odds ratios calculated using multivariable logistic regression. For VISION, the odds ratio was adjusted for age, sex, race and ethnicity, geographic region, and calendar time (days since January 1, 2021). The no updated dose group included all eligible persons who did not receive an updated 20232024 COVID-19 vaccine dose, regardless of number of previous (i.e., original monovalent and bivalent) doses (if any) received.

Abbreviations: IVY=Investigating Respiratory Viruses in the Acutely Ill; Ref=referent group; VE=vaccine effectiveness; VISION=Virtual SARS-CoV-2, Influenza, and Other respiratory viruses Network. * VE was calculated as (1 odds ratio) 100% with odds ratios calculated using multivariable logistic regression. For VISION, the odds ratio was adjusted for age, sex, race and ethnicity, geographic region, and calendar time (days since January 1, 2021). For IVY, the odds ratio was adjusted for age, sex, race and ethnicity, calendar time in biweekly intervals, and U.S. Department of Health and Human Services region. The no updated dose group included all eligible persons who did not receive an updated 20232024 COVID-19 vaccine dose, regardless of number of previous (i.e., original monovalent and bivalent) doses (if any) received. Some estimates are imprecise, which might be due to a relatively small number of persons in each level of vaccination or case status. This imprecision indicates that the actual VE could be substantially different from the point estimate shown, and estimates should therefore be interpreted with caution. Additional data accrual could increase precision and allow more precise interpretation.

Suggested citation for this article: DeCuir J, Payne AB, Self WH, et al. Interim Effectiveness of Updated 20232024 (Monovalent XBB.1.5) COVID-19 Vaccines Against COVID-19Associated Emergency Department and Urgent Care Encounters and Hospitalization Among Immunocompetent Adults Aged 18 Years VISION and IVY Networks, September 2023January 2024. MMWR Morb Mortal Wkly Rep 2024;73:180188. DOI: http://dx.doi.org/10.15585/mmwr.mm7308a5.

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Interim Effectiveness of Updated 20232024 (Monovalent XBB.1.5) COVID-19 Vaccines Against COVID-19Associated ... - CDC