Cristina Bergamaschi et al. characterized cytokine and chemokine responses to the Pfizer mRNA vaccine after the first and second dose in antigen-naive and COVID-19-infected individuals and identified increases in IL-15, IFN-γ, and IP-10/CXCL10 after the first vaccination dose, indicating antibody responses to spike-RBD and trimeric spike on the day of vaccination, which was not followed by a further increase in antibody responses upon the second vaccination dose, remained significantly higher than those in the SARS-CoV-2-naive vaccine recipients. Here, CXCL10 is linked to COVID-19.