Table 2.
Cycle threshold comparisons by Delta and Omicron variants
| Mean unadjusted difference in Orf1b Ct value (95% CI) | p-valueb | Mean adjusted difference in Orf1b Ct value (95% CI)a | p-valueb | |
|---|---|---|---|---|
| All Delta and Omicron positive individuals, adjusted for age, symptoms, and average RNase P gene value N = 1870 (Delta = 182, Omicron = 1688) | ||||
| Variant (Omicron vs. Delta) | 1.30 (0.76, 1.84) | 2.5 × 10−6 | 1.07 (0.58, 1.57) | 2.5 × 10−5 |
| Age (years) | −0.01 (−0.03, 0.01) | 0.29 | −0.01 (−0.03, 0.01) | 0.22 |
| Symptoms (symptomatic vs. asymptomatic) | −0.94 (−1.35, -0.53) | 8.2 × 10−6 | −1.11 (−1.50, −0.74) | 9.3 × 10−9 |
| Average RNase P gene value | 0.39 (0.35, 0.43) | 2.3 × 10−63 | 0.39 (0.35, 0.43) | 9.3 × 10−65 |
| Symptomatic individuals (with symptom onset on or before day of swab) adjusted for age, days since symptom onset, and average RNase P gene value N = 1466 (Delta = 144, Omicron = 1322) | ||||
| Variant (Omicron vs. Delta) | 1.08 (0.48, 1.68) | 0.0004 | 0.81 (0.26, 1.37) | 0.004 |
| Age (years) | −0.01 (−0.03, 0.01) | 0.44 | −0.01 (−0.03, 0.01) | 0.29 |
| Days since symptom onset | 0.32 (0.22, 0.41) | 1.8 × 10−10 | 0.29 (0.20, 0.38) | 1.6 × 10−10 |
| Average RNase P gene value | 0.40 (0.35, 0.45) | 3.2 × 10−54 | 0.39 (0.34, 0.44) | 1.2 × 10−52 |
| Vaccinated individuals (complete primary series or booster dose at time of swab), adjusted for age, symptoms status, vaccination status, days since last COVID-19 vaccine dose, and average RNase P gene value N = 1025 (Delta = 84, Omicron = 941) | ||||
| Variant (Omicron vs. Delta) | 1.26 (0.47, 2.05) | 0.001 | 0.87 (0.08, 1.67) | 0.03 |
| Age (years) | −0.003 (−0.03, 0.02) | 0.74 | −0.01 (−0.03, 0.01) | 0.48 |
| Symptoms (symptomatic vs. asymptomatic) | −1.27 (−2.86, −0.16) | 0.00001 | −1.41 (−1.93, −0.88) | 1.6 × 10−7 |
| Booster vaccination vs. Complete primary series vaccination | 0.71 (0.19, 1.22) | 0.007 | 0.50 (−0.55, 1.54) | 0.35 |
| Days since last COVID-19 vaccine dose | −0.002 (−0.005, −0.0004) | 0.02 | −0.001 (−0.006, 0.003) | 0.57 |
| Average RNase P gene value | 0.37 (0.31, 0.43) | 7.8 × 10−33 | 0.38 (0.32, 0.44) | 3.8 × 10−35 |
aMean adjusted differences estimated using three multiple linear regression of average Orf1b Ct value on variant (Omicron vs. Delta) adjusted by covariates indicated in the table above. All regressions were restricted to Delta and Omicron cases detected using RHINOsticTM swabs (excludes 27 Delta and 42 Omicron cases detected using US Cotton #3 swabs).
bTwo-sided t statistic with significance level of 0.05.
Bold values represent statistical significance p < 0.05.