Can Patients Develop Varicella Rash After Chickenpox and Shingles Vaccines?
Yes, patients can develop a varicella-like rash after receiving varicella (chickenpox) vaccine, though this occurs infrequently and is typically mild. The vaccine-strain rash appears in approximately 3-5% of vaccinees, occurring at a median of 21 days post-vaccination (range 5-42 days), with a median of 5 lesions 1.
Distinguishing Vaccine-Strain vs. Wild-Type Rash
When evaluating post-vaccination rash, timing is critical for determining the cause:
- Wild-type varicella rash: Occurs at a median of 8 days post-vaccination (range 1-24 days) and represents actual chickenpox infection acquired around the time of vaccination 1
- Vaccine-strain rash: Occurs later at a median of 21 days post-vaccination (range 5-42 days) and is caused by the attenuated vaccine virus 1
PCR analysis confirmed that the majority of rash events occurring within 42 days of vaccination during the first 4 years of the vaccination program were caused by wild-type virus, not vaccine strain 1.
Characteristics of Vaccine-Associated Rash
The vaccine-related rash has distinct features:
- Lesion count: Typically presents with approximately 5 lesions (median), though can range from 0-23 lesions 1
- Timing: Two peaks of occurrence—7-21 days and 0-23 days post-vaccination 1
- Severity: Generally mild and self-limited 1
- Location: May occur at injection site (2.3% with MMRV vaccine) or generalized 1, 2
Transmission Risk from Vaccinated Individuals
Transmission of vaccine virus from vaccinated persons to susceptible contacts is extremely rare but possible 1:
- Only 8 documented cases of vaccine virus transmission have been reported since program implementation, all from persons who developed a rash after vaccination 1
- No transmission has been documented from vaccinated healthcare personnel 1
- Risk is increased only in vaccinees who develop a varicella-like rash after vaccination, though even this risk remains low 1
Management of Healthcare Personnel with Post-Vaccination Rash
Healthcare workers who develop a vaccine-related rash should follow specific precautions 1:
- Avoid contact with persons without evidence of immunity who are at risk for severe disease and complications
- Duration of precautions: Until all lesions resolve (are crusted over), or if lesions don't crust (macules and papules only), until no new lesions appear within a 24-hour period 1
- Recently vaccinated healthcare personnel without rash require no work restrictions 1
Herpes Zoster (Shingles) After Vaccination
Herpes zoster can occur after varicella vaccination, but at substantially lower rates than after natural infection 1:
- Post-vaccination rate: 2.6 per 100,000 vaccine doses distributed 1
- Post-natural infection rate: 68 per 100,000 person-years in children <20 years, and 215 per 100,000 person-years for all ages 1
- Onset range for PCR-confirmed herpes zoster after vaccination: 25-722 days 1
Studies in leukemic children (a sentinel population) suggest vaccination may actually reduce the risk of zoster compared to natural infection 3.
Serious Adverse Events
Severe complications from vaccine-strain virus are rare and include 1:
- Pneumonia
- Hepatitis
- Severe disseminated varicella infection
- Secondary transmission (5 documented cases)
Critical caveat: These severe cases occurred almost exclusively in immunocompromised patients or persons with undiagnosed serious medical conditions at the time of vaccination 1.
Clinical Implications for Two-Dose Vaccination
The incidence of varicella-like rashes is lower after a second dose of MMRV (0.0%) compared to concomitant administration of separate MMR and varicella vaccines as second doses (1.9%) 1. The CDC now recommends two doses administered 4-8 weeks apart for optimal protection 4.
Common Pitfalls to Avoid
- Do not assume all post-vaccination rashes are vaccine-related: Most rashes occurring within 2 weeks are wild-type virus 1
- Do not unnecessarily restrict vaccinated healthcare workers: Only those with visible rash require precautions 1
- Do not confuse mild localized reactions with true varicella: Injection site reactions (erythema, swelling) are common and do not represent varicella 2