Chickenpox is a highly contagious illness caused by the varicella zoster virus, which produces an itchy, blister-like rash and lasts about five to 10 days. Other symptoms include fever, fatigue and headache.

The virus spreads in the air when an infected person coughs or sneezes, but can also be contracted by touching or breathing in the virus particles from chickenpox blisters, according to the U.S. Centers for Disease Control.

"Chickenpox is usually a mild, self-limiting illness," said Wormsbecker.

"However, chickenpox in some cases — and we can't predict in which cases — can result in very serious complications, including infections of the skin and deeper tissues, the most serious being necrotizing fasciitis."

Those skin and tissue infections are caused by different types of bacteria, likely introduced when a child scratches a blister, she said.

Necrotizing fasciitis, or flesh-eating disease, is a potentially life-threatening infection caused by the group A streptococcus bacterium and can be severe enough to require surgery or, in some cases, limb amputation.

But the virus itself can also cause complications, by infecting the lungs, brain or bloodstream and organs, resulting in disability or death in rare cases.

"So that to me is a reminder that it's important to have the chickenpox vaccine, and I'm really happy to see that our vaccine is working," said Wormsbecker.