TGFB1 and Recurrent upper respiratory tract infections: Given TGFβ1 is upregulated in severe COVID-19, we measured serum levels of TGFβ1 in the paediatric cohorts and compared them to previously published data on TGFβ1 in healthy young adults (below 30 years of age), patients with upper respiratory tract infection and SARS-CoV-2-infected adults with varying disease severity4 (Fig. 1b).