Decision‐Making Regarding the Administration of Live Vaccines to Patients With a <i>FOXN1</i> Heterozygous Missense Variant

This study discusses the decision-making process for administering live vaccines to an infant with a heterozygous FOXN1 missense variant, identified through newborn screening. The infant initially showed low T-cell receptor excision circle (TREC) levels, suggesting severe combined immunodeficiency (SCID), but had no physical abnormalities. Despite low initial TREC levels, the child's immune function improved over time, with CD4+ counts remaining above 500/μL and TREC levels normalizing by 8 months. Consequently, live vaccines were administered at 16 months, except for Bacillus Calmette–Guérin (BCG), with successful antibody responses and no adverse events. The study highlights the importance of repetitive TREC quantification and individual immune assessment in vaccine decision-making for patients with FOXN1-Het variants.