Chickenpox (varicella), which infects millions of children each year in the United States, is the disease most frequently confused with smallpox. There are key differences between the two diseases:
SMALLPOX (Variola)
CHICKENPOX (Varicella)
Smallpox incubation
7-17 days
Chickenpox incubation
14-21 days
Smallpox prodrome
(illness prior to rash)
2-4 days
Chickenpox prodrome
(illness prior to rash)
minimal/none
Smallpox distribution
1. Lesions initially tend to develop on the face and extremities, progressing to the trunk of the body.
2. Rash found on palms and soles.
Chickenpox distribution
1. Lesions initially tend to develop on the trunk of the body, progressing to the face and extremities. Lesions also tend to be more abundant on trunk than on face and extremities.
2. Rash rarely found on palms and soles.
Smallpox depth of rash
Deeply embedded
Chickenpox depth of rash
Superficial
Smallpox progression of rash
Lesions develop and progress at the same rate.
Chickenpox progression of rash
Lesions appear successively and progress at varying rates.
Smallpox scab formation
10-14 days after rash onset
Chickenpox scab formation
4-7 days after rash onset
Smallpox scab separation
14-28 days after rash onset
Chickenpox scab separation
<14 days after rash onset
Smallpox communicable period
From rash onset until all scabs have separated (3-4 weeks after onset of rash). Most infectious during the first week of rash, after prodrome.
Chickenpox communicable period
As long as 5 days (but usually 1-2 days) before rash onset until all lesions are crusted (usually) about 5 days after rash onset). Most infectious 1-2 days before rash onset and for first few days of rash.
For further information regarding smallpox:
contact Orange County Public Health/Epidemiology: (714) 834-8180
