Reply to: correspondence on "Herpes Zoster and Simplex reactivation following COVID-19 vaccination: new insights from a vaccine adverse event reporting system (VAERS) database analysis"

Background A few cases of Herpes Zoster and Simplex reactivation following COVID-19 immunization have been recently described, but the real extent of this suspected adverse event has not been elucidated yet. Methods We performed a nested case/control study by using the U.S. Vaccine Adverse Event Reporting System database. We carried out a case-level clinical review of all Herpes reactivation cases following the administration of COVID-19 vaccines. For cases and controls, significance was set at P = 0.05, differential risk of reporting was assessed for each vaccine as reporting odds ratio and incidence was estimated based on the total number of vaccine doses administered. Results Of 6,195 cases included in the analysis (5,934 and 273 reporting Herpes Zoster and Herpes Simplex, respectively) over 90% were non-serious. We found a slightly higher risk of reporting both for Zoster (ROR = 1.49) and Simplex (ROR = 1.51) infections following the Pfizer-BioNTech vaccine. The estimated incidence was approximately 0.7/100,000 and 0.03/100,000 for Zoster and Simplex, respectively. Conclusions The paucity of cases (almost all of non-serious nature) makes the potential occurrence of this adverse effect negligible from clinical standpoints, thus supporting the good safety profile of the COVID-19 vaccination, which remains strongly recommended.