Beyond the Scar: What Can a Persistent <scp>BCG</scp> Vaccine Reaction in Infants Tell Us in an Immunological Point of View?

The aim of this study was to evaluate children who still have not yet developed scar at the BCG vaccination site 16 weeks after vaccine administration without any local and systemic adverse reactions. The files of all children who were born between 01 Jan 2018 and 31 Dec 2023 were evaluated. BCG vaccine reaction status at the 6th month (completion with formation of scar or persistent reaction or abortive reaction), if any, further investigations performed in children with persistent BCG vaccine reaction without local or systemic adverse reactions; immunoglobulin (Ig) G, IgM, IgA, complete blood count, lymphocyte subgroup examination results, follow-up results and reaction completion time, and diagnoses were recorded. In our retrospective cohort study, the files of 962 children were evaluated. Of the 962 children, 22 of them had persistent BCG vaccine reaction at 6th months of age. Four of 22 children had low levels of IgG, IgM and IgA; 4 had low levels of both IgA and IgG; 3 had low levels of only IgG. There was no statistical significance in terms of blood count, birth weight, gender, BCG vaccine administration time, exclusively breastfeeding duration between children with persistent BCG reaction with low Ig levels and normal Ig levels. BCG reaction completion mean day was 268 (±33.3). Nine of 22 were diagnosed with transient hypogammaglobulinemia of infant (THI). Our study shows that THI may be considered in persistent BCG reactions without local or systemic adverse reactions. Further studies are needed for evaluating persistent BCG reactions.