A 67-year-old female with chronic neurotrophic keratitis developed her most severe exacerbation of herpes zoster keratitis in over 10 years occurring 2-3 weeks after her first Moderna (mRNA-1273) vaccine, which was later complicated by bacterial superinfection.<h4>Conclusions</h4>The COVID-19 vaccines work by generating both adaptive humoral and cellular immune responses in humans, including elevation of anti-spike neutralizing antibody titers, antigen-specific CD4+ and CD8+ T-cell responses, and increased levels of proinflammatory cytokines such as interferon gamma (IFN<i>γ</i>). This evidence concerns the gene CD4 and COVID-19.