Hello, I can understand your concern. The virus of chicken pox can transmit to another person even before the infected person presents with the clinical lesion. As your daughter has lesions now, the virus may have transmitted already to the son and thus, it is late to do anything to prevent your son from getting the infection. Even if he shows with the lesion, it is not fatal to life and can be managed with supportive therapy for lesions and fever. As this is a viral infection, it usually resolves on its own within 7 days. In case your son has not got the infection, you can try to keep separate rooms for your son and daughter and make sure that your daughter or any of her belongings do not come in contact with your son. Wash her clothes separately in warm water with disinfectant. I hope this information helps you. Thank you for choosing HCM. I wish your daughter feels well soon. Best, Dr. Viraj Shah