Partial IFNAR1 deficiency should therefore be considered in patients with unexplained severe viral illnesses, such as LAV disease, critical COVID-19 pneumonia, HSE, and JEV encephalitis, and in those with other unexplained severe viral infections, including critical influenza and MERS pneumonia, or with WNV encephalitis and TBE, which are seen in patients with auto-Abs against type I IFNs. Here, IFNAR1 is linked to herpes simplex encephalitis.