Risk of Herpes Zoster After Varicella Vaccination
Individuals vaccinated against varicella have a significantly lower risk of developing herpes zoster compared to those who acquire natural chickenpox infection, with vaccine recipients experiencing approximately one-third the incidence of zoster compared to naturally infected individuals.
Individual-Level Risk Reduction
Direct Comparison Data
The most compelling evidence comes from studies in immunocompromised populations where the risk is most apparent:
Vaccine recipients develop herpes zoster at approximately 0.80 per 100 person-years, compared to 2.46 per 100 person-years in those with natural varicella infection (p = 0.01), representing a three-fold reduction in risk 1.
In leukemic children followed for a mean of 4.1 years, only 2% of vaccine recipients developed zoster compared to 15% of controls with natural varicella history 1.
Long-term follow-up of healthy adults vaccinated 10-26 years ago shows an incidence of 1.00 case per 1,000 person-years, similar to baseline population rates in the prevaccine era 2.
Mechanism of Protection
The vaccine-strain virus (Oka strain) can establish latency and potentially reactivate, but does so at substantially lower rates than wild-type virus 1. This protective effect likely results from:
- Lower viral load established during initial vaccination compared to natural infection 1
- Maintained cell-mediated immunity against VZV reactivation 1
Population-Level Effects
Herd Immunity Benefits
Widespread varicella vaccination creates additional protective mechanisms at the population level:
Prevention of wild-type VZV infection eliminates the risk for wild-type herpes zoster in both vaccinated and unvaccinated individuals through herd immunity 1.
Reduction in early childhood varicella infections (particularly before age 18 months) decreases a known risk factor for childhood herpes zoster 1.
Surveillance Data Shows Stable Zoster Rates
Despite theoretical concerns about reduced immune boosting from decreased varicella exposure, population surveillance has not demonstrated increased herpes zoster incidence:
Age-adjusted herpes zoster incidence remained stable from 1992-2002 as varicella incidence decreased, with rates of 4.1 per 1,000 person-years in 1992 and 3.7 per 1,000 person-years in 2002 1.
National incidence data from 2000-2001 showed 3.2 per 1,000 person-years, representing no increase compared to earlier published data 1.
Important Clinical Caveats
Breakthrough Infections
- Individuals who develop varicella infection despite vaccination (breakthrough infection) are presumably latently infected with both vaccine and wild-type strains, though the herpes zoster risk in this population remains unknown 1.
Dose-Related Questions
No long-term studies have compared herpes zoster risk between recipients of 1 versus 2 doses of varicella vaccine 1.
Limited data from leukemic children suggests multiple vaccine doses may provide additional protection, with household varicella exposure and receipt of >1 vaccine dose both being highly protective (p < 0.01) 3.
Age-Related Risk Considerations
The risk and manifestation of vaccine-strain herpes zoster in older vaccinated adults requires ongoing monitoring, as this population faces greater risk for complications including postherpetic neuralgia 1.
Herpes zoster risk increases markedly starting at age 50 and peaks after age 60, with lifetime risk approaching 50% in those over 85 years 4.
Clinical Bottom Line
Varicella vaccination substantially reduces future herpes zoster risk compared to natural infection. The vaccine-strain virus can theoretically reactivate, but does so at rates approximately one-third those of wild-type virus. Population-level surveillance confirms no increase in overall herpes zoster incidence despite widespread vaccination programs. For vaccinated individuals who reach older adulthood (≥50 years), separate herpes zoster vaccination (Shingrix or Zostavax) remains indicated to further reduce risk 4, 5, 6.