Chickenpox Infectious Period
An infected person is contagious from 1 to 2 days before the rash appears until all skin lesions have crusted over, typically 5 to 7 days after rash onset. 1
Timeline of Contagiousness
Pre-Rash Period (Highest Risk)
- Transmission begins 1-2 days before any visible rash appears, making early identification and isolation challenging 1
- During this prodromal phase, the virus spreads through respiratory droplets and direct contact, even though no skin lesions are visible 1
- This pre-symptomatic transmission explains why school exclusion policies have limited effectiveness in controlling outbreaks 2
Active Rash Period
- Contagiousness continues throughout the vesicular stage when fluid-filled lesions are present 1
- The virus is present in respiratory secretions and vesicular fluid during this time 3
- Fever and rash typically last approximately 5 days 1
End of Contagious Period
- Infectivity ends when all lesions have completely crusted over, with no new lesions appearing 1
- This typically occurs 5-7 days after rash onset in immunocompetent individuals 4, 5
- For non-crusting lesions (macules and papules only), the patient is no longer contagious when no new lesions appear within a 24-hour period 4
Special Populations with Extended Infectious Periods
Immunocompromised Patients
- Healing may take 7-14 days or longer, significantly extending the contagious period 4
- These patients experience prolonged viral shedding and slower lesion crusting 4
- Progressive varicella (new lesions developing for >7 days) indicates continued viral replication and extended contagiousness 4
Neonates and High-Risk Infants
- Newborns whose mothers develop varicella from 5 days before to 2 days after delivery face severe disease with 17-30% developing severe infection 4
- Infants under 1 year are 6 times more likely to require hospitalization than older children 6
Transmission Characteristics
Contagiousness Level
- Chickenpox is extremely contagious, with 80-90% of susceptible household contacts developing infection after exposure 1, 6
- The household attack rate is approximately 85% (range 65-100%) among susceptible contacts 6
- More than 90% of unvaccinated people will become infected during their lifetime 7
Routes of Transmission
- Direct contact with vesicular fluid is the primary transmission route 1, 4
- Airborne droplets and respiratory secretions spread the virus efficiently 1
- The virus enters through the upper respiratory tract or conjunctivae 1, 4
Isolation Recommendations
General Population
- Isolate until all lesions have crusted, typically 5-7 days after rash onset 5
- Keep away from immunocompromised individuals, pregnant women without immunity, and newborns during the entire contagious period 5
Healthcare Workers
- Healthcare workers with chickenpox must be excluded from duty until all lesions are completely crusted 4
- Standard and contact precautions are required, with complete lesion coverage 4
Common Pitfalls to Avoid
- Do not assume the patient is non-contagious just because the rash has appeared—they were already contagious 1-2 days before 1
- Do not allow return to school or work based solely on symptom improvement—wait until all lesions are fully crusted 1, 5
- Do not underestimate transmission risk in immunocompromised patients, who may shed virus for weeks longer than immunocompetent individuals 4
- Do not rely on school exclusion policies alone to control outbreaks, as substantial transmission occurs before rash recognition 2