Chickenpox, a disease caused by the varicella-zoster virus, has been doing something the amazes scientists: it has been dropping since 2006 ever since the medical community began recommending a second dose of chickenpox vaccine, according to the Centers for Disease Control and Prevention.

There has been an 85 percent drop in chickenpox between 2005-2006 and 2013-2014, the CDC says, and the drop was biggest in kids between the ages of 5 and 14, which is the age group that is most likely to get a second dose of the varicella vaccine.

Chickenpox produces an itchy, blistery rash as well as fever and fatigue, and it can be dangerous for very young people, old people, and those with weakened immune systems..

Chickenpox was quite common in the United States before the vaccine had been developed, as 4 million Americans got it annually in the 1990, with 13,500 hospitalizations and up to 150 deaths per year. But vaccination has reduced that to 3.5 million cases, 9,000 hospitalizations and 100 deaths annually.

“Some people should not get chickenpox vaccine or should wait,” the CDC acknowledges. “People should not get chickenpox vaccine if they have ever had a life-threatening allergic reaction to a previous dose of chickenpox vaccine or to gelatin or the antibiotic neomycin. People who are moderately or severely ill at the time the shot is scheduled should usually wait until they recover before getting chickenpox vaccine. Pregnant women should wait to get chickenpox vaccine until after they have given birth. Women should not get pregnant for 1 month after getting chickenpox vaccine.”