Diagnosing inborn error of immunity following the presentation of a complicated acquired infection after MMRV vaccine administration.

Live vaccine-acquired infection should attest for the occurrence of inborn errors of immunity. Autosomal recessive immunodeficiency 31B, a result of a signal transducer and activator of transcription 1 genetic mutation, results in defected interferon pathways: interferon alpha/beta and interferon gamma. These interferons are crucial for the defence against viral and mycobacterial infections. Recognition is important for preventive and therapeutic approaches. Herein, we report the presentation of a newly diagnosed 13-month-old child with immunodeficiency 31B after presenting with disseminated measles and varicella infection after Measles, Mumps, Rubella and Varicella vaccination. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.