Association Between Child Varicella Vaccination and Zoster in Household Adults: A Retrospective Japanese Cohort Study

Aim: Some countries are hesitant to implement routine varicella vaccination for children because of concerns over the exogenous boosting hypothesis, which suggests that vaccinating children may increase herpes zoster cases in adults. However, substantial evidence supporting this hypothesis is lacking. This study assessed the association between a child's varicella vaccination status and herpes zoster occurrence in adults in the same household.

Methods: This retrospective cohort study analysed data from a Japanese city between April 2014 and December 2022. We included individuals aged ≥ 18 years living in households with a single child eligible for varicella vaccination. Children's vaccination status was categorised as unvaccinated, first-dose vaccinated or second-dose vaccinated. Cox regression analysis with time-dependent exposure assessed herpes zoster incidence in adults.

Results: Among 4023 eligible individuals, 136 (3.4%) developed herpes zoster over the median follow-up of 552 days. Neither the first nor the second dose of varicella vaccine in children was significantly associated with an increased risk of herpes zoster in adults (hazard ratio 1.24 [95% confidence interval, 0.69-2.23] for the first dose and 1.51 [0.87-2.62] for the second dose).

Conclusion: Varicella vaccination in households with a single child was not significantly associated with an increased risk of herpes zoster in adults.