Decision-Making Regarding the Administration of Live Vaccines to Patients With a FOXN1 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. Genetic analysis revealed a FOXN1-Het variant, which can range from healthy to severe immunodeficiency. The infant's immune function was monitored, and inactivated vaccines were administered initially. Live vaccines were given at 16 months, except for Bacillus Calmette–Guérin (BCG), after TREC levels normalized and CD4+ counts remained stable. The study highlights the importance of TREC quantification in guiding vaccine administration decisions for patients with FOXN1-Het variants.