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].