Table 3. COVID-19 Characteristics Among Unvaccinated Participants by SARS-CoV-2 Lineage.
| Characteristica | No. (%) | Difference (95% CI) | ||||
|---|---|---|---|---|---|---|
| Origin strains | Delta | Omicron | Delta vs origin | Omicron vs origin | Omicron vs Delta | |
| Asymptomatic SARS-CoV-2b | 19/165 (11.5) | 3/78 (3.9) | 22/109 (20.2) | OR, 0.36 (0.1 to 1.1)c | 1.8 (0.9 to 3.6) | 5.6 (1.6 to 19.6) |
| Symptoms, mean (SD)d,e | 7.7 (3.4) [n = 142] | 9 (3.9) [n = 73] | 6.9 (3.1) [n = 81] | 1.3 (0.3 to 2.3)f | −0.60 (−1.5 to 0.4) | −1.9 (−3.0 to −0.8) |
| Fever or chillsd,g | 102/142 (71.8) | 62/73 (84.9) | 64/81 (79) | OR, 2.2 (1.0 to 4.8)c | 1.6 (0.8 to 3.1) | 0.71 (0.3 to 1.7) |
| Received medical care for COVID-19 d,h | 52/141 (36.9) | 35/74 (47.3) | 20/81 (24.7) | OR, 1.8 (1.0 to 3.2)c | 0.69 (0.4 to 1.3) | 0.39 (0.2 to 0.8) |
| Duration of COVID-19 symptoms, mean (SD)i | 15.6 (9.4) [n = 144] | 16.4 (8.6) [n = 74] | 12.3 (9.1) [n = 85] | 0.80 (−1.9 to 3.4)f | −2.9 (−5.5 to −0.3) | −3.6 (−6.6 to −0.7) |
| Time spent sick in bed for at least half a day, mean (SD), dj | 4.3 (4.3) [n = 120] | 4.9 (4.6) [n = 58] | 2.6 (3.1) [n = 71] | 0.8 (−0.5 to 2.1)f | −1.2 (−2.5 to 0.0) | −2.0 (−3.4 to −0.6) |
| Time missed work due to COVID-19, mean (SD), hj | 54.5 (41.4) [n = 120] | 62.8 (35.0) [n = 58] | 35.9 (31.5) [n = 72] | 6.3 (−5.0 to 17.6)k | −19.2 (−29.8 to −8.6) | −25.5 (−8.0 to −13.0) |
| Viral RNA load, mean (SD), log10 copies/μL | 3.9 (1.7) [n = 165] | 4.0 (1.8) [n = 78] | 3.5 (1.8) [n = 109] | 0.18 (−0.31 to 0.68)f | −0.30 (−0.77 to 0.16) | −0.49 (−1.03 to 0.06) |
| Plaque-forming units, mean (SD), log10 copies/mL | 3.5 (1.0) [n = 9] | 4.8 (1.4) [n = 36] | 1.7 (0.7 to 2.7)f | |||
Illness characteristics are limited to unvaccinated participants to describe the natural history of infection without the vaccine-induced changes to immunity or the potential attenuation from vaccination.
Asymptomatic compared with COVID-19–like illness symptoms or non-COVID-19–like illness symptoms.
Odds ratios estimated using logistic regression with Ancestral strains as the referent participant group adjusted for number of daily medications and race and ethnicity.
Assessed among participants who reported COVID-19–like symptoms and responded to the illness survey.
Participants were asked about the following: fever or feeling feverish, chills, dry cough, cough that produces phlegm or sputum, sore throat, runny nose or nasal congestion, shortness of breath or difficulty breathing, muscle or body aches, joint pain, abdominal pain, nausea or queasy feeling that you may vomit, vomiting, diarrhea, headache, fatigue, rash, discoloration or blistering of fingers or toes, eye redness, and loss of smell or taste.
Mean difference estimated with linear regression adjusted for number of daily medications and race and ethnicity.
Fever or chills defined as self-reported fever, feverishness, chills, or measured temperature higher than 38 °C.
Among 296 unvaccinated participants who received medical care, including 273 who received outpatient care, 15 who went to the emergency department, and 8 who were hospitalized; 8 participants who did not report whether medical care was received during illness are excluded.
Assessed among participants who reported COVID-19–like symptoms.
Assessed among participants who reported COVID-19–like symptoms and responded to questions on days spent sick in bed for at least half a day and hours of missed work.
Mean difference estimated with linear regression adjusted for number of daily medications, race and ethnicity, and occupation.