A pilot observational study reported rare IRF7 variants detected exclusively among fully vaccinated patients who developed severe or critical COVID-19. In the cohort, 9 of 13 severely or critically ill vaccinated patients carried at least one IRF7 variant, compared with controls exhibiting mild or asymptomatic infection. The research focuses on host genetics in type I interferon signaling—an immune defense pathway previously linked to severe SARS-CoV-2 outcomes. The study also screened TLR7 in male participants, aiming to identify whether rare regulatory variants could help explain breakthrough severity. While limited by sample size, the findings add to evidence that genetics may contribute to risk stratification in immunized patients who still experience severe disease.