Search

Background The 2022–2023 United States influenza season had unusually early influenza activity with high hospitalization rates. Vaccine-matched A(H3N2) viruses predominated, with lower levels of A(H1N1)pdm09 activity also observed. Methods Using the test-negative design, we evaluated influenza vaccine effectiveness (VE) during the 2022–2023 season against influenza A–associated emergency department/urgent care (ED/UC) visits and hospitalizations from October 2022 to March 2023 among adults (aged ≥18 years) with acute respiratory illness (ARI). VE was estimated by comparing odds of seasonal influenza vaccination among case-patients (influenza A test positive by molecular assay) and controls (influenza test negative), applying inverse-propensity-to-be-vaccinated weights. Results The analysis included 85 389 ED/UC ARI encounters (17.0% influenza A positive; 37.8% vaccinated overall) and 19 751 hospitalizations (9.5% influenza A positive; 52.8% vaccinated overall). VE against influenza A–associated ED/UC encounters was 44% (95% confidence interval [CI], 40%–47%) overall and 45% and 41% among adults aged 18–64 and ≥65 years, respectively. VE against influenza A–associated hospitalizations was 35% (95% CI, 27%–43%) overall and 23% and 41% among adults aged 18–64 and ≥65 years, respectively. Conclusions VE was moderate during the 2022–2023 influenza season, a season characterized with increased burden of influenza and co-circulation with other respiratory viruses. Vaccination is likely to substantially reduce morbidity, mortality, and strain on healthcare resources. [ABSTRACT FROM AUTHOR]

Background: The epidemiology of coronavirus disease 2019 (COVID-19) continues to develop with emerging variants, expanding population-level immunity, and advances in clinical care. We describe changes in the clinical epidemiology of COVID-19 hospitalizations and risk factors for critical outcomes over time., Methods: We included adults aged ≥18 years from 10 states hospitalized with COVID-19 June 2021-March 2023. We evaluated changes in demographics, clinical characteristics, and critical outcomes (intensive care unit admission and/or death) and evaluated critical outcomes risk factors (risk ratios [RRs]), stratified by COVID-19 vaccination status., Results: A total of 60 488 COVID-19-associated hospitalizations were included in the analysis. Among those hospitalized, median age increased from 60 to 75 years, proportion vaccinated increased from 18.2% to 70.1%, and critical outcomes declined from 24.8% to 19.4% (all P < .001) between the Delta (June-December, 2021) and post-BA.4/BA.5 (September 2022-March 2023) periods. Hospitalization events with critical outcomes had a higher proportion of ≥4 categories of medical condition categories assessed (32.8%) compared to all hospitalizations (23.0%). Critical outcome risk factors were similar for unvaccinated and vaccinated populations; presence of ≥4 medical condition categories was most strongly associated with risk of critical outcomes regardless of vaccine status (unvaccinated: adjusted RR, 2.27 [95% confidence interval {CI}, 2.14-2.41]; vaccinated: adjusted RR, 1.73 [95% CI, 1.56-1.92]) across periods., Conclusions: The proportion of adults hospitalized with COVID-19 who experienced critical outcomes decreased with time, and median patient age increased with time. Multimorbidity was most strongly associated with critical outcomes., Competing Interests: Potential conflicts of interest. M. G. reports additional grants or institutional contracts with the CDC Ambulatory US Flu/COVID Vaccine Effectiveness (VE) Network, Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) Adult Inpatient Flu/COVID VE, Investigating Respiratory Viruses in the Acutely Ill Public Health Surveillance Network, and Researching COVID to Enhance Recovery and Health and Human Services Protect. C. M. reports an institutional grant or contract from AstraZeneca (AZD1222) for a COVID-19 vaccination trial. A. L. N. reports institutional research funding from Pfizer for an unrelated study of meningococcal B vaccine safety during pregnancy and Vir Biotechnology for an unrelated influenza study. S. A. I. reports an additional pending contract with CDC (200-2012-53584, Vaccine Safety Datalink). G. V.-B. reports grants or contracts from CDC (Vaccine Safety Datalink) and Sanofi (Tdap Vaccine Safety). A. B. K. reports a subcontract through HealthPartners for VISION payment made to Children's Minnesota. B. E. D. reports a grant from the National Institutes of Health to evaluate Health Information Exchange (HIE) technologies, a grant from CDC to use HIE data for public health surveillance, an R21 grant from the US Agency for Healthcare Research and Quality to evaluate HIE technologies, a grant from the US Department of Veterans Affairs to evaluate HIE technologies, royalties from Elsevier and Springer Nature for books on HIE and public health informatics, and consulting fees for advisory panel on human papillomavirus vaccination from Merck and Co. K. M. reports 2 additional contracts with CDC (Ambulatory US Flu VE Network and HAIVEN). N. P. K. has received grants from Pfizer, Merck, GlaxoSmithKline, and Sanofi Pasteur. S. R. has received grant funds from GlaxoSmithKline. P. K. M., V. L., and E. B. report payments made to Westat via CDC (contract number 200-2019-F-06819). C. M., C. R., D. K., E. S., G. V.-B., J. A., J. Han., K. S. A., K. N., K. D., M. B., M. B. D., M. M., M. S. S., N. G., N. R. V., P. J. E., S. G., T. C. O., and W. F. F. report payments made to their institution by CDC via Westat. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (Published by Oxford University Press on behalf of Infectious Diseases Society of America 2023.)