What is the management approach for a young adult with non-mild breakthrough varicella (chickenpox) who received a single dose of varicella vaccine 20 years ago at 15 months of age?

Understanding Non-Mild Breakthrough Varicella After Single-Dose Vaccination

Having non-mild breakthrough chickenpox after a single vaccine dose 20 years ago means this young adult is experiencing a wild-type varicella infection with clinical features similar to unvaccinated individuals—approximately 25-30% of breakthrough cases present this way, and this patient requires antiviral treatment given the severity and their age. 1

What Breakthrough Varicella Means

Breakthrough disease is defined as wild-type varicella-zoster virus (VZV) infection occurring more than 42 days after vaccination. 1

Why This Patient Developed Non-Mild Disease

• Single-dose vaccine efficacy is only approximately 85% against any varicella disease, leaving 15% of recipients without adequate protection 1
• The patient received only one dose 20 years ago when the standard was different—current recommendations call for two doses, which provide 98.3% efficacy compared to 94.4% for single dose 1
• Time since vaccination matters: Children vaccinated more than 5 years previously are 2.6 times more likely to have moderate-to-severe breakthrough varicella compared to those vaccinated more recently 1
• While most breakthrough cases are mild (70-75%), approximately 25-30% are NOT mild and have clinical features similar to unvaccinated children, including more lesions, fever, and longer duration of illness 1

Clinical Characteristics of Non-Mild Breakthrough Disease

• Non-mild cases can have >50 lesions (compared to the typical <50 in mild breakthrough cases) 1
• These patients may have vesicular lesions rather than the atypical papular rash seen in mild breakthrough cases 1
• Fever and systemic symptoms are more common in non-mild breakthrough disease 1
• Duration of illness is longer compared to mild breakthrough cases 1

Management Approach for This Young Adult

Antiviral Treatment is Indicated

For adults with varicella (including breakthrough cases), oral acyclovir 800 mg five times daily for 5 days is the standard treatment, and should be initiated within 24 hours of rash onset for maximum benefit. 2

• Treatment is most effective when started within the first 24 hours of rash onset, though benefit may still occur if started within 72 hours 2
• Varicella disease is more severe and complications more frequent among adolescents and adults compared to children, making treatment particularly important in this age group 1
• The patient's non-mild presentation warrants treatment regardless of vaccination history 1

Key Treatment Considerations

• Assess for risk factors that increase severity: history of asthma or eczema requiring steroids, as two deaths from breakthrough varicella occurred in children receiving steroid therapy 1
• Monitor for complications: pneumonia, encephalitis, and secondary bacterial infections are more common in adults 1
• Ensure isolation precautions: breakthrough varicella is contagious, with transmission rates to susceptible contacts similar to wild-type disease 1
• Avoid salicylates due to Reye syndrome risk (though this is primarily a pediatric concern) 3

Post-Recovery Vaccination Recommendation

After recovery, this patient should receive a second dose of varicella vaccine to complete the two-dose series and prevent future episodes. 1, 4

• The minimum interval between doses for persons ≥13 years is 4 weeks (28 days) 1, 4
• Two doses provide 3.3-fold lower risk of breakthrough disease compared to one dose 1
• After two doses, >99% of individuals achieve protective antibody levels compared to 76-85% after single dose 1
• Natural infection does not replace the need for completing the vaccine series in someone who was previously vaccinated, as the goal is optimal long-term protection 4

Important Clinical Pitfalls

• Do not assume all breakthrough cases are mild—25-30% present with features similar to unvaccinated individuals 1
• Do not delay antiviral treatment while waiting for laboratory confirmation in adults with clinical varicella 2
• Do not confuse this with vaccine-strain rash, which occurs within 42 days of vaccination and is typically very mild 1
• Seropositivity after single-dose vaccination does not guarantee complete protection, particularly in high-exposure situations or with waning immunity over time 5