Vitamin D Imbalance and Hydro-Electrolyte Disturbances in Hospitalized Children: A Comparation Between Post-COVID-19 Status and SARS-CoV-2/EBV Coinfection

<b>Background/Objectives:</b> SARS-CoV-2 infection has the potential to cause multi-organ involvement and, when associated with Epstein-Barr virus (EBV) coinfection, may worsen the course of disease in pediatric patients by influencing the immune response. <b>Methods:</b> Our retrospective-observational study included 406 hospitalized children with post-COVID-19 status or SARS-CoV-2/EBV coinfection. <b>Results:</b> Hypovitaminosis D was more common in the coinfected sublot (59.18%) than in the COVID-19 one (50.74%), with a higher frequency of severe vitamin D deficiency (16.33% vs. 7.35%). Hypovitaminosis D was significantly associated with female sex (<i>p</i> = 0.033) only in the COVID-19 subgroup. Hypervitaminosis D, although rare, was only associated with severe forms of the disease (7.69%). Between clinical severity and vitamin D level, a statistically significant association of moderate intensity was identified only in the COVID-19 subgroup (χ² = 11.708, φ = 0.293, <i>p</i> = 0.020). In the same subgroup, a significant correlation was found between vitamin D levels and serum potassium values (χ² = 10.527, <i>p</i> = 0.032). Moreover, in the COVID-19 subgroup, an association between abnormal sodium levels and increased D-dimer levels was found (χ² = 7.074, <i>p</i> = 0.029). <b>Conclusions:</b> These results underline the importance of monitoring immunologic, vitamin, and electrolyte imbalance in the management of these cases and highlight the need for personalized therapeutic strategies to prevent long-term complications.