Chickenpox

A 6-year-old unvaccinated boy presents with a 3-day history of low-grade fever, malaise, and headache followed by an intensely pruritic rash that began on the scalp and face and spread centripetally to the trunk. On examination, he is febrile (38.7°C) but non-toxic appearing. Cutaneous examination reveals hundreds of discrete lesions in various stages of evolution across the trunk, scalp, and face with characteristic centripetal distribution. The individual lesions marked **A** in the diagram show the classic appearance described as "dewdrops on a rose petals." Which of the following best describes the morphology and clinical significance of the lesions marked **A**?