IFNG and infection: Finally, regarding the effect of breakthrough infections on immunity, SARS-CoV-2 infections after the second or the third vaccine dose increased the S1-specific T cell response compared to individuals who remained naïve throughout the study (Figures 3A–C, S5A–D), and, as expected, also induced the development of IFN-γ T cells against SARS-CoV-2 M and N proteins (Figures S5E, F).