What is the risk of herpes zoster in individuals less than 50 years old without a history of chickenpox (varicella)?

Risk of Herpes Zoster in Adults Under 50 Without Chickenpox History

Individuals under 50 years old without a documented history of chickenpox have a very low actual risk of herpes zoster because most adults (88-91%) have been exposed to varicella zoster virus (VZV) even without recalled chickenpox, making them capable of developing shingles. 1

Understanding the True Risk

The question of herpes zoster risk in this population requires understanding the distinction between reported history and actual VZV exposure:

Seroprevalence Data Reveals Hidden Exposure

• Seroprevalence studies demonstrate that 88-91% of adults have VZV antibodies even when they don't recall having chickenpox, indicating subclinical or forgotten childhood infection. 1
• In Taiwan specifically, varicella seropositivity reached 88% in adults aged 21-30 years in the pre-vaccine era, meaning the vast majority without recalled chickenpox history were actually VZV-exposed. 1
• More recent data shows varicella seroprevalence of 72-88% among healthcare workers, confirming that most adults claiming no chickenpox history are actually VZV-seropositive. 1

Actual Risk Profile

For truly VZV-seronegative individuals (the minority without chickenpox history):

• These individuals have essentially zero risk of herpes zoster because you cannot reactivate a virus you've never been infected with. 1
• Herpes zoster only occurs through reactivation of latent VZV that remains dormant in dorsal root ganglia after primary varicella infection. 1

For VZV-seropositive individuals without recalled chickenpox (the majority):

• These individuals have the same herpes zoster risk as anyone else with prior VZV exposure, with baseline incidence of 4.97 cases per 1000 person-years in the general adult population. 1
• Risk increases with age, immunosuppression, and comorbidities (diabetes, rheumatoid arthritis, SLE, cancer, HIV). 1

Clinical Implications for Management

Vaccination Approach Based on Age and Immune Status

For immunocompetent adults under 50 without chickenpox history:

• No routine herpes zoster vaccination is recommended, as standard zoster vaccines (both ZVL and RZV) are approved for ages 50 and older. 1
• Consider varicella vaccination if confirmed VZV-seronegative by serology, using 2 doses separated by 4 weeks. 1
• Screening for varicella serology is not routinely recommended given the high seroprevalence, but can be considered if planning immunosuppressive therapy. 1

For immunocompromised adults under 50:

• RZV can be administered to adults aged 18 and older who are or will be immunocompromised, regardless of chickenpox history. 1
• For immunocompromised patients under 50, consider checking varicella serology and vaccination history before administering RZV. 1
• If confirmed VZV-seronegative, prioritize varicella vaccine (2 doses) over zoster vaccine. 1

For adults aged 50 and older without chickenpox history:

• Herpes zoster vaccination with RZV is recommended regardless of chickenpox history, as both ZVL and RZV are safe and immunogenic in VZV-seronegative individuals. 1, 2
• Do not screen for varicella history or conduct serologic testing before zoster vaccination in immunocompetent adults 50 and older. 1, 2

Key Clinical Pitfalls to Avoid

• Don't assume absence of recalled chickenpox means VZV-seronegative status - most adults have been exposed even without clinical disease. 2
• Don't unnecessarily delay appropriate vaccination to conduct varicella serology in immunocompetent adults aged 50 and older. 2
• Don't administer live zoster vaccine (ZVL) to immunocompromised patients, even if VZV-seronegative - use RZV instead or consider varicella vaccine. 1
• Don't give live varicella vaccine during immunosuppressive therapy - it requires a 4-week window before starting immunosuppression and should be avoided for 3 months after stopping. 1

Special Considerations for Immunosuppressive Therapy

If planning to start immunosuppressive therapy in adults under 50:

• Check varicella immunity status (history, serology, or prior vaccination documentation). 1
• If VZV-seronegative and time permits, administer 2 doses of varicella vaccine at least 4 weeks before starting immunosuppression. 1
• If no time for vaccination, counsel patients to avoid chickenpox/zoster exposure and seek post-exposure prophylaxis (aciclovir for 7 days starting 7 days after exposure) if exposed. 1