8. Reactivation of Varicella-zoster
Type I IFN receptor signaling in CD8+ T cells is critical for the generation of effector and memory cells in response to a viral infection [134]. CD8+ T cells can block reactivation of latent herpes infection in sensory neurons [135]. If type I IFN signaling is impaired, as happens following vaccination but not following natural infection with SARS-CoV-2, CD8+ T cells’ ability to keep herpes in check would also be impaired. Might this be the mechanism at work in response to the vaccines?
Shingles is an increasingly common condition caused by reactivation of latent herpes zoster viruses (HZV), which also causes chicken pox in childhood. In a systematic review, Katsikas et al., (2021) identified 91 cases of herpes zoster occurring an average of 5.8 days following mRNA vaccination [136]. While acknowledging that causality is not yet confirmed, “Herpes zoster is possibly a condition physicians and other healthcare professionals may expect to see in patients receiving COVID-19 vaccines” [136]. In a letter to the editor published in September 20201, Fathy et al. (2021) reported on 672 cases of skin reactions that were presumably vaccine-related, including 40 cases of herpes zoster and/or herpes simplex reactivation [137]. These cases had been reported to the American Academy of Dermatology and the International League of Dermatologic Societies’ COVID-19 Dermatology Registry, established specifically to track dermatological sequalae from the vaccines. There are multiple additional case reports of herpes zoster reactivation following COVID-19 vaccination in the literature [138,139]. Lladó et al. (2021) noted that 51 of 52 reports of reactivated herpes zoster infections happened following mRNA vaccination [140]. Herpes zoster itself also interferes with IFN-α signaling in infected cells both through interfering with STAT2 phosphorylation and through facilitating IRF9 degradation [141].
An additional case of viral reactivation is noteworthy as well. It involved an 82-year-old woman who had acquired a hepatitis C viral (HCV) infection in 2007. A strong increase in HCV load occurred a few days after vaccination with an mRNA Pfizer/BioNTech vaccine, along with an appearance of jaundice. She died three weeks after vaccination from liver failure [142].