Subsequent investigation of the senescent CD28-CD57+ Tc population revealed an increased ratio in IPF sufferers (14.03% vs 3.76%; p=0.003 before vaccination; 16.11% vs 3.93%; p=0.001 after the 1st dose; 14.36% vs 4.46%; p=0.005 after the 2nd dose). Here, CD28 is linked to idiopathic pulmonary fibrosis.