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Item Early Estimates of Bivalent mRNA Vaccine Effectiveness in Preventing COVID-19–Associated Emergency Department or Urgent Care Encounters and Hospitalizations Among Immunocompetent Adults — VISION Network, Nine States, September–November 2022(Center for Disease Control, 2022-12-30) Tenforde, Mark W.; Weber, Zachary A.; Natarajan, Karthik; Klein, Nicola P.; Kharbanda, Anupam B.; Stenehjem, Edward; Embi, Peter J.; Reese, Sarah E.; Naleway, Allison L.; Grannis, Shaun J.; DeSilva, Malini B.; Ong, Toan C.; Gaglani, Manjusha; Han, Jungmi; Dickerson, Monica; Fireman, Bruce; Dascomb, Kristin; Irving, Stephanie A.; Vazquez-Benitez, Gabriela; Rao, Suchitra; Konatham, Deepika; Patel, Palak; Schrader, Kristin E.; Lewis, Ned; Grisel, Nancy; McEvoy, Charlene; Murthy, Kempapura; Griggs, Eric P.; Rowley, Elizabeth A. K.; Zerbo, Ousseny; Arndorfer, Julie; Dunne, Margaret M.; Goddard, Kristin; Ray, Caitlin; Zhuang, Yan; Timbol, Julius; Najdowski, Morgan; Yang, Duck-Hye; Hansen, John; Ball, Sarah W.; Link-Gelles, Ruth; Biomedical Engineering and Informatics, Luddy School of Informatics, Computing, and EngineeringDuring June-October 2022, the SARS-CoV-2 Omicron BA.5 sublineage accounted for most of the sequenced viral genomes in the United States, with further Omicron sublineage diversification through November 2022.* Bivalent mRNA vaccines contain an ancestral SARS-CoV-2 strain component plus an updated component of the Omicron BA.4/BA.5 sublineages. On September 1, 2022, a single bivalent booster dose was recommended for adults who had completed a primary vaccination series (with or without subsequent booster doses), with the last dose administered ≥2 months earlier (1). During September 13-November 18, the VISION Network evaluated vaccine effectiveness (VE) of a bivalent mRNA booster dose (after 2, 3, or 4 monovalent doses) compared with 1) no previous vaccination and 2) previous receipt of 2, 3, or 4 monovalent-only mRNA vaccine doses, among immunocompetent adults aged ≥18 years with an emergency department/urgent care (ED/UC) encounter or hospitalization for a COVID-19-like illness.† VE of a bivalent booster dose (after 2, 3, or 4 monovalent doses) against COVID-19-associated ED/UC encounters was 56% compared with no vaccination, 31% compared with monovalent vaccination only with last dose 2-4 months earlier, and 50% compared with monovalent vaccination only with last dose ≥11 months earlier. VE of a bivalent booster dose (after 2, 3, or 4 monovalent doses) against COVID-19-associated hospitalizations was 57% compared with no vaccination, 38% compared with monovalent vaccination only with last dose 5-7 months earlier, and 45% compared with monovalent vaccination only with last dose ≥11 months earlier. Bivalent vaccines administered after 2, 3, or 4 monovalent doses were effective in preventing medically attended COVID-19 compared with no vaccination and provided additional protection compared with past monovalent vaccination only, with relative protection increasing with time since receipt of the last monovalent dose. All eligible persons should stay up to date with recommended COVID-19 vaccinations, including receiving a bivalent booster dose. Persons should also consider taking additional precautions to avoid respiratory illness this winter season, such as masking in public indoor spaces, especially in areas where COVID-19 community levels are high.Item Effectiveness of 2, 3, and 4 COVID-19 mRNA Vaccine Doses Among Immunocompetent Adults During Periods when SARS-CoV-2 Omicron BA.1 and BA.2/BA.2.12.1 Sublineages Predominated — VISION Network, 10 States, December 2021–June 2022(Center for Disease Control, 2022-07-22) Link-Gelles, Ruth; Levy, Matthew E.; Gaglani, Manjusha; Irving, Stephanie A.; Stockwell, Melissa; Dascomb, Kristin; DeSilva, Malini B.; Reese, Sarah E.; Liao, I-Chia; Ong, Toan C.; Grannis, Shaun J.; McEvoy, Charlene; Patel, Palak; Klein, Nicola P.; Hartmann, Emily; Stenehjem, Edward; Natarajan, Karthik; Naleway, Allison L.; Murthy, Kempapura; Rao, Suchitra; Dixon, Brian E.; Kharbanda, Anupam B.; Akinseye, Akintunde; Dickerson, Monica; Lewis, Ned; Grisel, Nancy; Han, Jungmi; Barron, Michelle A.; Fadel, William F.; Dunne, Margaret M.; Goddard, Kristin; Arndorfer, Julie; Konatham, Deepika; Valvi, Nimish R.; Currey, J. C.; Fireman, Bruce; Raiyani, Chandni; Zerbo, Ousseny; Sloan-Aagard, Chantel; Ball, Sarah W.; Thompson, Mark G.; Tenforde, Mark W.; Epidemiology, Richard M. Fairbanks School of Public HealthThe Omicron variant (B.1.1.529) of SARS-CoV-2, the virus that causes COVID-19, was first identified in the United States in November 2021, with the BA.1 sublineage (including BA.1.1) causing the largest surge in COVID-19 cases to date. Omicron sublineages BA.2 and BA.2.12.1 emerged later and by late April 2022, accounted for most cases.* Estimates of COVID-19 vaccine effectiveness (VE) can be reduced by newly emerging variants or sublineages that evade vaccine-induced immunity (1), protection from previous SARS-CoV-2 infection in unvaccinated persons (2), or increasing time since vaccination (3). Real-world data comparing VE during the periods when the BA.1 and BA.2/BA.2.12.1 predominated (BA.1 period and BA.2/BA.2.12.1 period, respectively) are limited. The VISION network† examined 214,487 emergency department/urgent care (ED/UC) visits and 58,782 hospitalizations with a COVID-19-like illness§ diagnosis among 10 states during December 18, 2021-June 10, 2022, to evaluate VE of 2, 3, and 4 doses of mRNA COVID-19 vaccines (BNT162b2 [Pfizer-BioNTech] or mRNA-1273 [Moderna]) compared with no vaccination among adults without immunocompromising conditions. VE against COVID-19-associated hospitalization 7-119 days and ≥120 days after receipt of dose 3 was 92% (95% CI = 91%-93%) and 85% (95% CI = 81%-89%), respectively, during the BA.1 period, compared with 69% (95% CI = 58%-76%) and 52% (95% CI = 44%-59%), respectively, during the BA.2/BA.2.12.1 period. Patterns were similar for ED/UC encounters. Among adults aged ≥50 years, VE against COVID-19-associated hospitalization ≥120 days after receipt of dose 3 was 55% (95% CI = 46%-62%) and ≥7 days (median = 27 days) after a fourth dose was 80% (95% CI = 71%-85%) during BA.2/BA.2.12.1 predominance. Immunocompetent persons should receive recommended COVID-19 booster doses to prevent moderate to severe COVID-19, including a first booster dose for all eligible persons and second booster dose for adults aged ≥50 years at least 4 months after an initial booster dose. Booster doses should be obtained immediately when persons become eligible.Item Effectiveness of a Third Dose 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(U.S. Department of Health & Human Services, 2022-01-28) Thompson, Mark G.; Natarajan, Karthik; Irving, Stephanie A.; Rowley, Elizabeth A.; Griggs, Eric P.; Gaglani, Manjusha; Klein, Nicola P.; Grannis, Shaun J.; DeSilva, Malini B.; Stenehjem, Edward; Reese, Sarah E.; Dickerson, Monica; Naleway, Allison L.; Han, Jungmi; Konatham, Deepika; McEvoy, Charlene; Rao, Suchitra; Dixon, Brian E.; Dascomb, Kristin; Lewis, Ned; Levy, Matthew E.; Patel, Palak; Liao, I-Chia; Kharbanda, Anupam B.; Barron, Michelle A.; Fadel, William F.; Grisel, Nancy; Goddard, Kristin; Yang, Duck-Hye; Wondimu, Mehiret H.; Murthy, Kempapura; Valvi, Nimish R.; Arndorfer, Julie; Fireman, Bruce; Dunne, Margaret M.; Embi, Peter; Azziz-Baumgartner, Eduardo; Zerbo, Ousseny; Bozio, Catherine H.; Reynolds, Sue; Ferdinands, Jill; Williams, Jeremiah; Link-Gelles, Ruth; Schrag, Stephanie J.; Verani, Jennifer R.; Ball, Sarah; Ong, Toan C.; Family Medicine, School of MedicineItem Effectiveness of COVID-19 mRNA Vaccines Against COVID-19–Associated Hospitalizations Among Immunocompromised Adults During SARS-CoV-2 Omicron Predominance — VISION Network, 10 States, December 2021—August 2022(U.S. Department of Health & Human Services, 2022-10-21) Britton, Amadea; Embi, Peter J.; Levy, Matthew E.; Gaglani, Manjusha; DeSilva, Malini B.; Dixon, Brian E.; Dascomb, Kristin; Patel, Palak; Schrader, Kristin E.; Klein, Nicola P.; Ong, Toan C.; Natarajan, Karthik; Hartmann, Emily; Kharbanda, Anupam B.; Irving, Stephanie A.; Dickerson, Monica; Dunne, Margaret M.; Raiyani, Chandni; Grannis, Shaun J.; Stenehjem, Edward; Zerbo, Ousseny; Rao, Suchitra; Han, Jungmi; Sloan-Aagard, Chantel; Griggs, Eric P.; Weber, Zachary A.; Murthy, Kempapura; Fadel, William F.; Grisel, Nancy; McEvoy, Charlene; Lewis, Ned; Barron, Michelle A.; Nanez, Juan; Reese, Sarah E.; Mamawala, Mufaddal; Valvi, Nimish R.; Arndorfer, Julie; Goddard, Kristin; Yang, Duck-Hye; Fireman, Bruce; Ball, Sarah W.; Link-Gelles, Ruth; Naleway, Allison L.; Tenforde, Mark W.; Biomedical Engineering and Informatics, Luddy School of Informatics, Computing, and EngineeringItem Effectiveness of COVID-19 Pfizer-BioNTech BNT162b2 mRNA Vaccination in Preventing COVID-19–Associated Emergency Department and Urgent Care Encounters and Hospitalizations Among Nonimmunocompromised Children and Adolescents Aged 5–17 Years — VISION Network, 10 States, April 2021–January 2022(Centers for Disease Control and Prevention, 2022-03-04) Klein, Nicola P.; Stockwell, Melissa S.; Demarco, Maria; Gaglani, Manjusha; Kharbanda, Anupam B.; Irving, Stephanie A.; Rao, Suchitra; Grannis, Shaun J.; Dascomb, Kristin; Murthy, Kempapura; Rowley, Elizabeth A.; Dalton, Alexandra F.; DeSilva, Malini B.; Dixon, Brian E.; Natarajan, Karthik; Stenehjem, Edward; Naleway, Allison L.; Lewis, Ned; Ong, Toan C.; Patel, Palak; Konatham, Deepika; Embi, Peter J.; Reese, Sarah E.; Han, Jungmi; Grisel, Nancy; Goddard, Kristin; Barron, Michelle A.; Dickerson, Monica; Liao , I-Chia; Fadel, William F.; Yang, Duck-Hye; Arndorfer, Julie; Fireman, Bruce; Griggs, Eric P.; Valvi, Nimish R.; Hallowell, Carly; Zerbo, Ousseny; Reynolds, Sue; Ferdinands, Jill; Wondimu, Mehiret H.; Williams, Jeremiah; Bozio, Catherine H.; Link-Gelles, Ruth; Azziz-Baumgartner, Eduardo; Schrag, Stephanie J.; Thompson, Mark G.; Verani, Jennifer R.; Family Medicine, School of MedicineItem Effectiveness of Homologous and Heterologous COVID-19 Booster Doses Following 1 Ad.26.COV2.S (Janssen [Johnson & Johnson]) Vaccine Dose Against COVID-19-Associated Emergency Department and Urgent Care Encounters and Hospitalizations Among Adults - VISION Network, 10 States, December 2021-March 2022(Center for Disease Control, 2022-04-01) Natarajan, Karthik; Prasad, Namrata; Dascomb, Kristin; Irving, Stephanie A.; Yang, Duck-Hye; Gaglani, Manjusha; Klein, Nicola P.; DeSilva, Malini B.; Ong, Toan C.; Grannis, Shaun J.; Stenehjem, Edward; Link-Gelles, Ruth; Rowley, Elizabeth A.; Naleway, Allison L.; Han, Jungmi; Raiyani, Chandni; Vazquez Benitez, Gabriela; Rao, Suchitra; Lewis, Ned; Fadel, William F.; Grisel, Nancy; Griggs, Eric P.; Dunne, Margaret M.; Stockwell, Melissa S.; Mamawala, Mufaddal; McEvoy, Charlene; Barron, Michelle A.; Goddard, Kristin; Valvi, Nimish R.; Arndorfer, Julie; Patel, Palak; Mitchell, Patrick K.; Smith, Michael; Kharbanda, Anupam B.; Fireman, Bruce; Embi, Peter J.; Dickerson, Monica; Davis, Jonathan M.; Zerbo, Ousseny; Dalton, Alexandra F.; Wondimu, Mehiret H.; Azziz-Baumgartner, Eduardo; Bozio, Catherine H.; Reynolds, Sue; Ferdinands, Jill; Williams, Jeremiah; Schrag, Stephanie J.; Verani, Jennifer R.; Ball, Sarah; Thompson, Mark G.; Dixon, Brian E.; Community and Global Health, Richard M. Fairbanks School of Public HealthCDC recommends that all persons aged ≥18 years receive a single COVID-19 vaccine booster dose ≥2 months after receipt of an Ad.26.COV2.S (Janssen [Johnson & Johnson]) adenovirus vector-based primary series vaccine; a heterologous COVID-19 mRNA vaccine is preferred over a homologous (matching) Janssen vaccine for booster vaccination. This recommendation was made in light of the risks for rare but serious adverse events following receipt of a Janssen vaccine, including thrombosis with thrombocytopenia syndrome and Guillain-Barré syndrome† (1), and clinical trial data indicating similar or higher neutralizing antibody response following heterologous boosting compared with homologous boosting (2). Data on real-world vaccine effectiveness (VE) of different booster strategies following a primary Janssen vaccine dose are limited, particularly during the period of Omicron variant predominance. The VISION Network§ determined real-world VE of 1 Janssen vaccine dose and 2 alternative booster dose strategies: 1) a homologous booster (i.e., 2 Janssen doses) and 2) a heterologous mRNA booster (i.e., 1 Janssen dose/1 mRNA dose). In addition, VE of these booster strategies was compared with VE of a homologous booster following mRNA primary series vaccination (i.e., 3 mRNA doses). The study examined 80,287 emergency department/urgent care (ED/UC) visits¶ and 25,244 hospitalizations across 10 states during December 16, 2021-March 7, 2022, when Omicron was the predominant circulating variant.** VE against laboratory-confirmed COVID-19-associated ED/UC encounters was 24% after 1 Janssen dose, 54% after 2 Janssen doses, 79% after 1 Janssen/1 mRNA dose, and 83% after 3 mRNA doses. VE for the same vaccination strategies against laboratory-confirmed COVID-19-associated hospitalizations were 31%, 67%, 78%, and 90%, respectively. All booster strategies provided higher protection than a single Janssen dose against ED/UC visits and hospitalizations during Omicron variant predominance. Vaccination with 1 Janssen/1 mRNA dose provided higher protection than did 2 Janssen doses against COVID-19-associated ED/UC visits and was comparable to protection provided by 3 mRNA doses during the first 120 days after a booster dose. However, 3 mRNA doses provided higher protection against COVID-19-associated hospitalizations than did other booster strategies during the same time interval since booster dose. All adults who have received mRNA vaccines for their COVID-19 primary series vaccination should receive an mRNA booster dose when eligible. Adults who received a primary Janssen vaccine dose should preferentially receive a heterologous mRNA vaccine booster dose ≥2 months later, or a homologous Janssen vaccine booster dose if mRNA vaccine is contraindicated or unavailable. Further investigation of the durability of protection afforded by different booster strategies is warranted.Item Estimation of COVID-19 mRNA Vaccine Effectiveness Against Medically Attended COVID-19 in Pregnancy During Periods of Delta and Omicron Variant Predominance in the United States(American Medical Association, 2022-09-01) Schrag, Stephanie J.; Verani, Jennifer R.; Dixon, Brian E.; Page, Jessica M.; Butterfield, Kristen A.; Gaglani, Manjusha; Vazquez-Benitez, Gabriela; Zerbo, Ousseny; Natarajan, Karthik; Ong, Toan C.; Lazariu, Victoria; Rao, Suchitra; Beaver, Ryan; Ellington, Sascha R.; Klein, Nicola P.; Irving, Stephanie A.; Grannis, Shaun J.; Kiduko, Salome; Barron, Michelle A.; Midturi, John; Dickerson, Monica; Lewis, Ned; Stockwell, Melissa S.; Stenehjem, Edward; Fadel, William F.; Link-Gelles, Ruth; Murthy, Kempapura; Goddard, Kristin; Grisel, Nancy; Valvi, Nimish R.; Fireman, Bruce; Arndorfer, Julie; Konatham, Deepika; Ball, Sarah; Thompson, Mark G.; Naleway, Allison L.; Epidemiology, School of Public HealthImportance: Pregnant people are at high risk for severe COVID-19 but were excluded from mRNA vaccine trials; data on COVID-19 vaccine effectiveness (VE) are needed. Objective: To evaluate the estimated effectiveness of mRNA vaccination against medically attended COVID-19 among pregnant people during Delta and Omicron predominance. Design, setting, and participants: This test-negative, case-control study was conducted from June 2021 to June 2022 in a network of 306 hospitals and 164 emergency department and urgent care (ED/UC) facilities across 10 US states, including 4517 ED/UC encounters and 975 hospitalizations among pregnant people with COVID-19-like illness (CLI) who underwent SARS-CoV-2 molecular testing. Exposures: Two doses (14-149 and ≥150 days prior) and 3 doses (7-119 and ≥120 days prior) of COVID-19 mRNA vaccine (≥1 dose received during pregnancy) vs unvaccinated. Main outcomes and measures: Estimated VE against laboratory-confirmed COVID-19-associated ED/UC encounter or hospitalization, based on the adjusted odds ratio (aOR) for prior vaccination; VE was calculated as (1 - aOR) × 100%. Results: Among 4517 eligible CLI-associated ED/UC encounters and 975 hospitalizations, 885 (19.6%) and 334 (34.3%) were SARS-CoV-2 positive, respectively; the median (IQR) patient age was 28 (24-32) years and 31 (26-35) years, 537 (12.0%) and 118 (12.0%) were non-Hispanic Black and 1189 (26.0%) and 240 (25.0%) were Hispanic. During Delta predominance, the estimated VE against COVID-19-associated ED/UC encounters was 84% (95% CI, 69% to 92%) for 2 doses within 14 to 149 days, 75% (95% CI, 5% to 93%) for 2 doses 150 or more days prior, and 81% (95% CI, 30% to 95%) for 3 doses 7 to 119 days prior; estimated VE against COVID-19-associated hospitalization was 99% (95% CI, 96% to 100%), 96% (95% CI, 86% to 99%), and 97% (95% CI, 79% to 100%), respectively. During Omicron predominance, for ED/UC encounters, the estimated VE of 2 doses within 14 to 149 days, 2 doses 150 or more days, 3 doses within 7 to 119 days, and 3 doses 120 or more days prior was 3% (95% CI, -49% to 37%), 42% (95% CI, -16% to 72%), 79% (95% CI, 59% to 89%), and -124% (95% CI, -414% to 2%), respectively; for hospitalization, estimated VE was 86% (95% CI, 41% to 97%), 64% (95% CI, -102% to 93%), 86% (95% CI, 28% to 97%), and -53% (95% CI, -1254% to 83%), respectively. Conclusions and relevance: In this study, maternal mRNA COVID-19 vaccination, including booster dose, was associated with protection against medically attended COVID-19. VE estimates were higher against COVID-19-associated hospitalization than ED/UC visits and lower against the Omicron variant than the Delta variant. Protection waned over time, particularly during Omicron predominance.Item Impact of accounting for correlation between COVID-19 and influenza vaccination in a COVID-19 vaccine effectiveness evaluation using a test-negative design(Elsevier, 2023) Payne, Amanda B.; Ciesla, Allison Avrich; Rowley, Elizabeth A. K.; Weber, Zachary A.; Reese, Sarah E.; Ong, Toan C.; Vazquez-Benitez, Gabriela; Naleway, Allison L.; Klein, Nicola P.; Embi, Peter J.; Grannis, Shaun J.; Kharbanda, Anupam B.; Gaglani, Manjusha; Tenforde, Mark W.; Link-Gelles, Ruth; VISION Network; Medicine, School of MedicineTest-negative-design COVID-19 vaccine effectiveness (VE) studies use symptomatic SARS-CoV-2-positive individuals as cases and symptomatic SARS-CoV-2-negative individuals as controls to evaluate COVID-19 VE. To evaluate the potential bias introduced by the correlation of COVID-19 and influenza vaccination behaviors, we assessed changes in estimates of VE of bivalent vaccines against COVID-19-associated hospitalizations and emergency department/urgent care (ED/UC) encounters when considering influenza vaccination status or including or excluding influenza-positive controls using data from the multi-state VISION vaccine effectiveness network. Analyses included encounters during October 2022 - February 2023, a period of SARS-CoV-2 and influenza cocirculation. When considering influenza vaccination status or including or excluding influenza-positive controls, COVID-19 VE estimates were robust, with most VE estimates against COVID-19-associated hospitalization and ED/UC encounters changing less than 5 percentage points. Higher proportions of influenza-positive patients among controls, influenza vaccination coverage, or VE could impact these findings; the potential bias should continue to be assessed.Item Investigating Health Disparities Associated With Multisystem Inflammatory Syndrome in Children After SARS-CoV-2 Infection(Wolters Kluwer, 2022) Zambrano, Laura D.; Ly, Kathleen N.; Link-Gelles, Ruth; Newhams, Margaret M.; Akande, Manzilat; Wu, Michael J.; Feldstein, Leora R.; Tarquinio, Keiko M.; Sahni, Leila C.; Riggs, Becky J.; Singh, Aalok R.; Fitzgerald, Julie C.; Schuster, Jennifer E.; Giuliano, John S., Jr.; Englund, Janet A.; Hume, Janet R.; Hall, Mark W.; Osborne, Christina M.; Doymaz, Sule; Rowan, Courtney M.; Babbitt, Christopher J.; Clouser, Katharine N.; Horwitz, Steven M.; Chou, Janet; Patel, Manish M.; Hobbs, Charlotte; Randolph, Adrienne G.; Campbell, Angela P.; Overcoming COVID-19 Investigators; Pediatrics, School of MedicineBackground: Multisystem inflammatory syndrome in children (MIS-C) is a postinfectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-related complication that has disproportionately affected racial/ethnic minority children. We conducted a pilot study to investigate risk factors for MIS-C aiming to understand MIS-C disparities. Methods: This case-control study included MIS-C cases and SARS-CoV-2-positive outpatient controls less than 18 years old frequency-matched 4:1 to cases by age group and site. Patients hospitalized with MIS-C were admitted between March 16 and October 2, 2020, across 17 pediatric hospitals. We evaluated race, ethnicity, social vulnerability index (SVI), insurance status, weight-for-age and underlying medical conditions as risk factors using mixed effects multivariable logistic regression. Results: We compared 241 MIS-C cases with 817 outpatient SARS-CoV-2-positive at-risk controls. Cases and controls had similar sex, age and U.S. census region distribution. MIS-C patients were more frequently previously healthy, non-Hispanic Black, residing in higher SVI areas, and in the 95th percentile or higher for weight-for-age. In the multivariable analysis, the likelihood of MIS-C was higher among non-Hispanic Black children [adjusted odds ratio (aOR): 2.07; 95% CI: 1.23-3.48]. Additionally, SVI in the 2nd and 3rd tertiles (aOR: 1.88; 95% CI: 1.18-2.97 and aOR: 2.03; 95% CI: 1.19-3.47, respectively) were independent factors along with being previously healthy (aOR: 1.64; 95% CI: 1.18-2.28). Conclusions: In this study, non-Hispanic Black children were more likely to develop MIS-C after adjustment for sociodemographic factors, underlying medical conditions, and weight-for-age. Investigation of the potential contribution of immunologic, environmental, and other factors is warranted.Item Methods to Adjust for Confounding in Test-Negative Design COVID-19 Effectiveness Studies: Simulation Study(JMIR, 2025-01-27) Rowley, Elizabeth A. K.; Mitchell, Patrick K.; Yang, Duck-Hye; Lewis, Ned; Dixon, Brian E.; Vazquez-Benitez, Gabriela; Fadel, William F.; Essien, Inih J.; Naleway, Allison L.; Stenehjem, Edward; Ong, Toan C.; Gaglani, Manjusha; Natarajan, Karthik; Embi, Peter; Wiegand, Ryan E.; Link-Gelles, Ruth; Tenforde, Mark W.; Fireman, Bruce; Health Policy and Management, Richard M. Fairbanks School of Public HealthBackground: Real-world COVID-19 vaccine effectiveness (VE) studies are investigating exposures of increasing complexity accounting for time since vaccination. These studies require methods that adjust for the confounding that arises when morbidities and demographics are associated with vaccination and the risk of outcome events. Methods based on propensity scores (PS) are well-suited to this when the exposure is dichotomous, but present challenges when the exposure is multinomial. Objective: This simulation study aimed to investigate alternative methods to adjust for confounding in VE studies that have a test-negative design. Methods: Adjustment for a disease risk score (DRS) is compared with multivariable logistic regression. Both stratification on the DRS and direct covariate adjustment of the DRS are examined. Multivariable logistic regression with all the covariates and with a limited subset of key covariates is considered. The performance of VE estimators is evaluated across a multinomial vaccination exposure in simulated datasets. Results: Bias in VE estimates from multivariable models ranged from -5.3% to 6.1% across 4 levels of vaccination. Standard errors of VE estimates were unbiased, and 95% coverage probabilities were attained in most scenarios. The lowest coverage in the multivariable scenarios was 93.7% (95% CI 92.2%-95.2%) and occurred in the multivariable model with key covariates, while the highest coverage in the multivariable scenarios was 95.3% (95% CI 94.0%-96.6%) and occurred in the multivariable model with all covariates. Bias in VE estimates from DRS-adjusted models was low, ranging from -2.2% to 4.2%. However, the DRS-adjusted models underestimated the standard errors of VE estimates, with coverage sometimes below the 95% level. The lowest coverage in the DRS scenarios was 87.8% (95% CI 85.8%-89.8%) and occurred in the direct adjustment for the DRS model. The highest coverage in the DRS scenarios was 94.8% (95% CI 93.4%-96.2%) and occurred in the model that stratified on DRS. Although variation in the performance of VE estimates occurred across modeling strategies, variation in performance was also present across exposure groups. Conclusions: Overall, models using a DRS to adjust for confounding performed adequately but not as well as the multivariable models that adjusted for covariates individually.