TABLE 2.

Different time courses of Original COVID-19 and Delta Variant.

	Original COVID-19	Delta variant
Incubation period (days before the onset of initial symptoms)	4 (2–7)	4 (3–5)
Early stage (days after the onset of initial symptoms)	0–4	0–3
Progressive and peak stage (days after the onset of initial symptoms)	5–13	4–16
Peak value of lung involvement	11	15
Absorption stage (days after the onset of initial symptoms)	14–28	17–42
Negative time of RT-PCR (days after the onset of initial symptoms)	22 (17–30)	39 (31–44)
Discharge time (days after the onset of initial symptoms)	28 (21–31)	42 (34–46)

Incubation period, negative time of RT-PCR, and discharge time are medians, with ranges of quartiles in parentheses. Incubation period is the interval between the potential earliest date of contact of the transmission source and the potential earliest date of symptom onset. Negative time of RT-PCR is the interval between the potential earliest date of symptom onset and the first negative date of RT-PCR. Discharge time is the interval between the potential earliest date of symptom onset and the discharge date.