Table 3.
Factors and their association with duration (days) of SARS-CoV-2 incubation period in univariable and multivariable linear regression models
| Univariable analysis | Multivariable analysis | |
|---|---|---|
| Sex | ||
| Male | 0 (ref) | 0 (ref) |
| Female | 0·04 (−0·03 to 0·1) | 0·1 (0·02 to 0·2) |
| Variant | ||
| Historical strain | 0 (ref) | 0 (ref) |
| Alpha | 0·3 (0·3 to 0·4) | 0·3 (0·3 to 0·4) |
| Beta or gamma | 0·6 (0·3 to 0·8) | 0·6 (0·3 to 0·8) |
| Delta | −0·2 (−0·3 to −0·1) | −0·1 (−0·2 to 0·03) |
| Omicron | −1·0 (−1·1 to −0·9) | −0·9 (−1·0 to −0·7) |
| Age, years | ||
| 18–29 | 0 (ref) | 0 (ref) |
| 30–39 | 0·1 (−0·01 to 0·2) | 0·1 (0·00 to 0·2) |
| 40–49 | 0·2 (0·1 to 0·3) | 0·2 (0·1 to 0·3) |
| 50–59 | 0·2 (0·1 to 0·3) | 0·2 (0·1 to 0·3) |
| 60–69 | 0·4 (0·3 to 0·5) | 0·4 (0·3 to 0·5) |
| ≥70 | 0·3 (0·1 to 0·5) | 0·4 (0·2 to 0·6) |
| Smoking status | ||
| Non-smoker, no nicotine substitution | 0 (ref) | 0 (ref) |
| Non-smoker, nicotine substitution | −0·2 (−0·5 to 0·2) | −0·2 (−0·5 to 0·2) |
| Non-smoker, electronic cigarette only | 0·1 (−0·1 to 0·3) | 0·2 (0·00 to 0·3) |
| <10 cigarettes per day | 0·1 (−0·04 to 0·2) | 0·1 (0·02 to 0·3) |
| 10–20 cigarettes per day | 0·2 (0·02 to 0·3) | 0·2 (0·1 to 0·4) |
| >20 cigarettes per day | 0·3 (0·1 to 0·5) | 0·4 (0·1 to 0·6) |
| COVID-19 vaccine status | ||
| Unvaccinated | 0 (ref) | 0 (ref) |
| One dose, <90 days since last injection | −0·2 (−0·5 to 0·02) | −0·2 (−0·4 to 0·1) |
| One dose, 90–179 days since last injection | −0·9 (−1·3 to −0·6) | −0·3 (−0·7 to 0·1) |
| One dose, ≥180 days since last injection | −1·0 (−1·4 to −0·6) | −0·5 (−0·9 to −0·1) |
| Two doses, <90 days since last injection | −0·2 (−0·4 to −0·1) | 0·1 (−0·1 to 0·3) |
| Two doses, 90–179 days since last injection | −0·6 (−0·7 to −0·5) | −0·1 (−0·3 to −0·03) |
| Two doses, ≥180 days since last injection | −0·7 (−0·8 to −0·5) | −0·2 (−0·4 to −0·05) |
| Three doses, <90 days since last injection | −0·8 (−0·1 to −0·7) | 0·01 (−0·2 to 0·2) |
| Three doses, 90–179 days since last injection | −0·8 (−1·5 to −0·2) | −0·3 (−0·9 to 0·3) |
| Three doses, ≥180 days since last injection | −1·2 (−2·3 to −0·1) | −0·6 (−1·3 to 0·1) |
| Four doses, <90 days since last injection | −0·4 (−2·3 to 2·1) | 0·5 (−2·3 to 3·3) |
| Undated last dose of vaccine | −0·2 (−0·6 to 0·2) | 0·2 (−0·3 to 0·7) |
| Previous SARS-CoV-2 infection | ||
| No | 0 (ref) | 0 (ref) |
| Yes, virologically or serologically confirmed | −0·5 (−0·7 to −0·3) | 0·01 (−0·2 to 0·2) |
| Yes, diagnosed on clinical evaluation only | −0·1 (−0·5 to 0·2) | −0·02 (−0·4 to 0·3) |
| Symptoms in index case | ||
| No | 0 (ref) | 0 (ref) |
| Yes | −0·1 (−0·2 to −0·1) | −0·1 (−0·2 to −0·1) |
| Mask wearing | ||
| Neither participant or index case | 0 (ref) | 0 (ref) |
| Index case only | 0·1 (−0·2 to 0·3) | −0·01 (−0·2 to 0·2) |
| Participant only | 0·3 (0·2 to 0·5) | 0·2 (0·1 to 0·4) |
| Both participant and index case | 0·2 (0·1 to 0·3) | 0·1 (0·03 to 0·2) |
| Setting of transmission | ||
| Indoors with closed windows | 0 (ref) | .. |
| Indoors with open windows | 0·00 (−0·1 to 0·1) | .. |
| Outdoors | 0·1 (−0·1 to 0·2) | .. |
| Underlying conditions | ||
| Chronic respiratory disease | 0·1 (−0·1 to 0·2) | .. |
| Hypertension | 0·2 (0·04 to 0·3) | .. |
| Underweight | −0·2 (−0·4 to −0·1) | .. |
| Diabetes | 0·2 (−0·1 to 0·4) | .. |
| Coronary artery disease | 0·03 (−0·3 to 0·4) | .. |
Data are coefficent (95% CI). The multivariable linear regression model was adjusted for all variables in the table. Underlying conditions and setting of transmission were not included in the multivariable model due to the absence of statistical significance. Robust SEs were applied to account for potential heteroscedasticity.