Department of Population Health Sciences, Albany College of Pharmacy & Health Sciences, Albany, New York.
Division of Infectious Diseases, Department of Pediatrics, University of Washington, Seattle.
JAMA Netw Open. 2023 Feb 1;6(2):e231181. doi: 10.1001/jamanetworkopen.2023.1181.
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.
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.
DESIGN, SETTING, AND PARTICIPANTS: 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.
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's geographic region.
MAIN OUTCOMES AND MEASURE(S): The main outcomes examined were the prevalence and severity of acute (≤28 days after onset) and postacute (≥5 weeks after onset) symptoms.
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 = .001). Compared with individuals infected during the Delta wave, individuals infected during the Omicron wave also experienced a 56% (95% CI, 26%-74%, P = .004) relative reduction in the risk of postacute symptoms and a 79% (95% CI, 54%-91%, P < .001) relative reduction in the rate of postacute symptoms.
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.
奥密克戎变异株在美国的出现导致了 SARS-CoV-2 感染的迅速增加。虽然许多研究报告了接种疫苗的个体或有先前感染的个体中奥密克戎感染的特征，但缺乏描述免疫原性未受影响的成年人感染的综合数据。
在奥密克戎（BA.1/BA.2）激增期间，研究一批未接种疫苗且先前未感染 SARS-CoV-2 的免疫原性未受影响的成年人中的 COVID-19 急性和后期临床结局，并将结果与德尔塔波期间发生的感染进行比较。
设计、地点和参与者：这项前瞻性多地点队列研究包括在美国 8 个州居住的成年人，他们在 2021 年 6 月至 2022 年 9 月期间接受高分辨率症状和病毒学监测。招募了 30 岁至 65 岁以下、无 SARS-CoV-2 免疫史且感染风险高的未接种疫苗的成年人。参与者最多随访 48 周，定期提交 COVID-19 症状调查，并提交鼻拭子进行 SARS-CoV-2 聚合酶链反应（PCR）检测。数据分析于 2022 年 5 月至 10 月进行。
奥密克戎（BA.1/BA.2 谱系）与德尔塔 SARS-CoV-2 感染，定义为阳性 PCR 检测结果，发生在变体在参与者所在地区的循环 SARS-CoV-2 变体中至少占 50%的时期。
主要研究结果是急性（发病后≤28 天）和后期（发病后≥5 周）症状的发生率和严重程度。
在 274 名免疫原性未受影响的参与者（平均[SD]年龄，49[9.7]岁；186[68%]女性；19[7%]西班牙裔参与者；242[88%]白人参与者）中，166 人（61%）感染了 SARS-CoV-2。其中，137 例（83%）感染发生在奥密克戎为主的时期，29 例（17%）感染发生在德尔塔为主的时期。奥密克戎波感染中无症状感染占 7%（95%CI，3%-12%），德尔塔波感染中无症状感染占 0%（95%CI，0%-12%）。奥密克戎波感染者的医疗保健使用率比德尔塔波感染者低 79%（95%CI，43%-92%）（P = .001）。与感染德尔塔波的个体相比，感染奥密克戎波的个体后期症状的风险也降低了 56%（95%CI，26%-74%，P = .004），后期症状的发生率降低了 79%（95%CI，54%-91%，P < .001）。
这些发现表明，在以前免疫原性未受影响的成年人中，奥密克戎波（BA.1/BA.2）和德尔塔波的感染很少无症状。与感染德尔塔波的个体相比，感染奥密克戎波的个体不太可能寻求医疗保健并出现后期症状。
