Final answer:
Chickenpox is a viral disease that affects 90% of American adults at some point. It is highly contagious and can lead to complications in adults. A vaccine is available to prevent chickenpox.
Step-by-step explanation:
About 90% of American adults had chickenpox before adulthood. Chickenpox, also known as varicella, is a viral disease caused by the varicella-zoster virus. It is highly contagious and is transmitted through direct contact or inhalation of material from the skin lesions. In children, the disease is mild, but in adults, it can be more severe and lead to complications such as pneumonia. A vaccine is available for both children and adults to prevent chickenpox.