I'm wondering why are adults more likely to get pneumonia from chicken pox (varicella pneumonia) than children are?

Because.: Many illnesses that are mild when they occur in childhood are more more severe when contracted as an adult. It may be that the immune response is over-reactive in the adult organism & that this hyper-response is at least partially responsible for the severity of symptoms in adults. Mononucleosus is typically worse when occurring in adults and adolescent. In younger children its just like a cold.

Chicken pox: Varicella is contagious and is trransmitted by coughing. The infected person will get sick a week later and develop a skin eruption with tiny blisters .Varicella occurs mostly in children, who rarely get pneumonia. Adults rarely get varicella at all since they are immune from their childhood infection. Those with immune disorders, . Hiv or leukemia, are often sicker and may get pneumonia.