The percentages of naïve Teffs within the CD4+ cell population were decreased in IPF (15.59% vs 25.04%; p= 0.04 before vaccination; 11.03% vs 25.85%; p=0.001 after the 1st dose; 14.36% vs 30.45%; p=0.001 after the 2nd dose). Here, CD4 is linked to idiopathic pulmonary fibrosis.