Though most children who get the itchy, highly contagious viral disease go on to recover after a week or so of misery, chickenpox can cause severe complications and even death in some. Complications include nasty skin infections, pneumonia, brain inflammation, hemorrhaging, blood stream infections, and dehydration.

If the infection strikes early in a pregnancy, there’s a small chance it could cause birth defects, including abnormally formed limbs, brain, eyes, and skull, as well as intellectual disabilities. If it strikes just before birth, a newborn has a 30 percent chance of getting a severe form of the disease, which can be fatal.

In addition to newborns, people who have an increased risk of severe complications from chickenpox include teens, adults, pregnant women, and people who have a weakened immune system, such as cancer patients on chemotherapy, transplant patients, and those with HIV/AIDS.