{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T03:20:47Z","timestamp":1790824847204,"version":"4.1.0"},"reference-count":26,"publisher":"American Medical Association (AMA)","issue":"2","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JAMA Netw Open"],"abstract":"Importance<\/jats:title>The US arrival of the Omicron variant led to a rapid increase in SARS-CoV-2 infections. While numerous studies report characteristics of Omicron infections among vaccinated individuals or persons with previous infection, comprehensive data describing infections among adults who are immunologically naive are lacking.<\/jats:p><\/jats:sec>Objectives<\/jats:title>To examine COVID-19 acute and postacute clinical outcomes among a well-characterized cohort of unvaccinated and previously uninfected adults who contracted SARS-CoV-2 during the Omicron (BA.1\/BA.2) surge, and to compare outcomes with infections that occurred during the Delta wave.<\/jats:p><\/jats:sec>Design, Setting, and Participants<\/jats:title>This prospective multisite cohort study included community-dwelling adults undergoing high-resolution symptom and virologic monitoring in 8 US states between June 2021 and September 2022. Unvaccinated adults aged 30 to less than 65 years without an immunological history of SARS-CoV-2 who were at high risk of infection were recruited. Participants were followed for up to 48 weeks, submitting regular COVID-19 symptom surveys and nasal swabs for SARS-CoV-2 polymerase chain reaction (PCR) testing. Data were analyzed from May to October 2022.<\/jats:p><\/jats:sec>Exposures<\/jats:title>Omicron (BA.1\/BA.2 lineages) vs Delta SARS-CoV-2 infection, defined as a positive PCR test result that occurred during a period when the variant represented at least 50% of circulating SARS-CoV-2 variants in the participant\u2019s geographic region.<\/jats:p><\/jats:sec>Main Outcomes and Measure(s)<\/jats:title>The main outcomes examined were the prevalence and severity of acute (\u226428 days after onset) and postacute (\u22655 weeks after onset) symptoms.<\/jats:p><\/jats:sec>Results<\/jats:title>Among 274 participants who were immunologically naive (mean [SD] age, 49 [9.7] years; 186 [68%] female; 19 [7%] Hispanic participants; 242 [88%] White participants), 166 (61%) contracted SARS-CoV-2. Of these, 137 infections (83%) occurred during the Omicron-predominant period and 29 infections (17%) occurred during the Delta-predominant period. Asymptomatic infections occurred among 7% (95% CI, 3%-12%) of Omicron-wave infections and 0% (95% CI, 0%-12%) of Delta-wave infections. Health care use among individuals with Omicron-wave infections was 79% (95% CI, 43%-92%) lower relative to individuals with Delta-wave infections (P<\/jats:italic>\u2009=\u2009.001). Compared with individuals infected during the Delta wave, individuals infected during the Omicron wave also experienced a 56% (95% CI, 26%-74%, P<\/jats:italic>\u2009=\u2009.004) relative reduction in the risk of postacute symptoms and a 79% (95% CI, 54%-91%, P<\/jats:italic>\u2009&amp;lt;\u2009.001) relative reduction in the rate of postacute symptoms.<\/jats:p><\/jats:sec>Conclusions and Relevance<\/jats:title>These findings suggest that among adults who were previously immunologically naive, few Omicron-wave (BA.1\/BA.2) and Delta-wave infections were asymptomatic. Compared with individuals with Delta-wave infections, individuals with Omicron-wave infections were less likely to seek health care and experience postacute symptoms.<\/jats:p><\/jats:sec>","DOI":"10.1001\/jamanetworkopen.2023.1181","type":"journal-article","created":{"date-parts":[[2023,2,28]],"date-time":"2023-02-28T16:02:19Z","timestamp":1677600139000},"page":"e231181","source":"Crossref","is-referenced-by-count":23,"title":["Acute and Postacute COVID-19 Outcomes Among Immunologically Naive Adults During Delta vs Omicron Waves"],"prefix":"10.1001","volume":"6","author":[{"given":"Margaret K.","family":"Doll","sequence":"first","affiliation":[{"name":"Department of Population Health Sciences, Albany College of Pharmacy & Health Sciences, Albany, New York"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alpana","family":"Waghmare","sequence":"additional","affiliation":[{"name":"Division of Infectious Diseases, Department of Pediatrics, University of Washington, 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