Question

A $48$-hour-old male neonate is evaluated in the well-baby nursery due to a newly developed, rapidly spreading rash. The infant was born at $39$ weeks gestation via spontaneous vaginal delivery to a $28$-year-old mother. The mother's prenatal history is notable for a primary genital herpes simplex virus infection at $14$ weeks gestation, which was treated with oral valacyclovir; she had no prodromal symptoms or active lesions at the time of delivery. The infant's vital signs are temperature $37.3^\circ\text{C}$ ($99.1^\circ\text{F}$), heart rate $142$/min, and respiratory rate $42$/min. He is breastfeeding vigorously and has normal tone. Skin examination reveals numerous $2$-mm to $3$-mm firm, pale-yellow pustules, each situated on a wide, blotchy erythematous base. The lesions are scattered over the thorax, abdomen, and proximal thighs, while the palms, soles, and oral mucosa remain entirely clear. A smear of the pustular contents is performed to rule out infectious etiologies, showing no microorganisms. Based on the most likely diagnosis, which of the following best describes the underlying pathophysiology of this infant's cutaneous findings?