Abstract
Herein, we report the case of a 67-year-old man with severe coronavirus disease (COVID-19) pneumonia and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine breakthrough infection during immunosuppressive therapy for connective tissue disease-related interstitial lung disease (CTD-ILD). The patient received glucocorticoids combined with tacrolimus as maintenance therapy. His serum anti-SARS-CoV-2-immunoglobulin G (IgG) antibody levels were extremely low at the onset of COVID-19 pneumonia, even after the second dose of SARS-CoV-2 mRNA vaccine (BNT162b2). After treatment for COVID-19 pneumonia, the levels of anti-SARS-CoV-2-IgG antibodies increased. These results indicated a lack of the ability to produce neutralising antibodies from immune cells despite the booster vaccination. Therefore, we suggest that advanced-age patients with CTD-ILD receiving immunosuppressive therapy with polypharmacy require consistent personal protection, vaccination of close caregivers, increased awareness, and booster vaccination. Moreover, we recommend that tacrolimus should be withdrawn for a while after vaccination under controlled conditions.