Patients with STAT2-deficient mutations have an impaired response to IFN-I and suffer from severe viral infections.28 Caused by missense mutations of STAT2, patients suffer from the condition called immunodeficiency 44, an autosomal recessive primary immunodeficiency characterized by increased susceptibility to viral infections and encephalopathy.29,30 Through ClinVar, we found that one third of the STAT2 mutations occur in the DBD, suggesting that this domain, which includes T404, is critical for a competent immune response, especially against virus infections. Here, STAT2 is linked to primary immunodeficiency with post-measles-mumps-rubella vaccine viral infection.