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Karen Wilcox was bewildered and concerned when a rash appeared on her daughter Chloe's torso.

The bumps resembled chicken pox, the Sandy mother thought, but her daughter had received a vaccination for the contagious disease as a baby.

Sure enough, when Wilcox brought Chloe to the doctor's office, her pediatrician confirmed that the then 4-year-old girl had a breakthrough case of chicken pox, also known as varicella.

"I was surprised," Wilcox said. "But even though she got it, it didn't last long - only a couple days. She wasn't itching intolerably, she didn't feel sick and she didn't have a fever. The vaccine made her case milder."

Health care experts estimate that the vaccine protects 85 percent to 90 percent of those who receive it, and for those who get the disease, the symptoms are less severe.

A new study in this month's issue of Pediatrics found that hospitalizations for chicken pox have declined since vaccination against varicella was recommended in 1995.

Using data from the Agency for Healthcare Research and Quality, which tracks hospitalizations, the study is the first nationally to show a link between childhood chicken pox vaccinations and reduced hospitalizations and hospital charges for children and adults.

During the study time frame, hospital costs dropped from $161.1 million in 1993 to $66.3 million in 2001. Varicella-related hospital charges accounted for 0.04 percent of all annual hospitalizations in 1993, compared with 0.01 percent in 2001.

Some parents are hesitant to have their children immunized because they view chicken pox as a part of childhood - an irksome inconvenience but perfectly survivable. However, the disease can cause complications, such as skin infections, and poses a greater risk for adults and children with weakened immune systems, landing some people in the hospital.

Doctors at Primary Children's Medical Center in Salt Lake City saw three children with complications from chicken pox last year and have seen one so far this year.

The Utah Department of Health doesn't track the number of chicken pox cases. Rebecca Ward, education outreach coordinator with the health department, said that while the vaccine isn't perfect, it is effective.

"When we asked parents why they had not vaccinated their children, the No. 1 reason was that the child's health care provider had not offered the varicella vaccine, and some parents didn't know it was available," Ward said.

In 2002, the state began requiring the vaccine for all kindergarten students.

Even so, many older children and adults who haven't contracted chicken pox were never inoculated against it. Once people are infected, they are immune to chicken pox.

Ward and many pediatricians recommend vaccination to avoid complications.

"Some parents had chicken pox when they were children, and they recalled they lived through it and were fine," said Sarah Croskell, a pediatrician at the University of Utah. "They don't see the disease as a threat. It's not actually the chicken pox that is as bad as the bacteria that infects them."

Croskell has seen patients wind up in the intensive care unit with staphylococcus or streptococcal A infections that have invaded open sores.

With the vaccine being so new, there are still unanswered questions. For example, if you are immunized as a child, can you still be the victim of an outbreak as an adult? And, if you have a breakthrough infection, can you still get shingles later in life?

Shingles occur when the dormant virus is reactivated, causing painful blisters generally on the back and underarms.

"We will have to wait for history to tell us that," Croskell said. "But for now, what I tell people is that I vaccinated my children."