Megan Cummins and her children enjoy snack time at their Chicago home.

Megan Cummins, with children Eva Preus, age 9, Solveig Preus, 6, and their brother, Kai Preus, 13 months, are shown in their Hyde Park apartment on the south side of Chicago. Megan has tried to expose her older kids to chickenpox to get the disease out of the way, but they haven't caught it.

Megan Cummins and her children enjoy snack time at their Chicago home.

Chicago ? As Tabitha Keller drove her two young children to attend a chickenpox party earlier this year, she felt a moment of doubt about the wisdom of intentionally infecting her kids with the bug.

Keller did not trust the chickenpox vaccine, so she was arranging for her children to get immunity the old-fashioned way, by catching the disease from an infected child and muddling through weeks of itchiness. Such chickenpox parties were also held in the pre-vaccine era because some experts argued it was safest for kids to get the disease early in life, when the effects tend to be relatively mild.

Although most pediatricians today advise against chickenpox parties, some parents who avoid the vaccination for medical or religious reasons seek out such get-togethers on Internet message boards. Those who have tried it say the strategy takes commitment, persistence and a dose of good luck.

Keller, a stay-at-home mom from Burbank, Ill., said going to the party also required resisting some of her instincts as a parent.

“It was so ironic and strange to be driving out to this house, hoping that my kids would get sick,” Keller said. “That’s pretty much what you spend your entire life avoiding.”

More important, the party did not work – a problem several parents said they have encountered. In fact, Keller’s 5-year-old daughter and 18-month-old son attended two parties in quick succession and failed to get sick from either one.

Getting kids infected can be harder than parents assume, experts said. Chickenpox is most contagious during a period of slightly more than one week, beginning a few days before lesions appear and lasting until scabs form on the chickenpox sores.

Some parents said they drove to an infected child’s house only to find that scabs had begun to form, making infection less likely. In addition, some children may get infected but never show symptoms.

Most pediatricians say the chickenpox vaccine is preferable to getting the disease because parents never know if their child will be unlucky enough to develop one of the disease’s rare but serious complications.

About 1 in 10 children with chickenpox has problems serious enough to see a doctor, ranging from skin infections and dehydration to pneumonia and encephalitis, according to the federal Centers for Disease Control and Prevention.

Doctors say some people should never be exposed to chickenpox, including infants, people with weakened immune systems and pregnant women.

Some parents said they believed their children were healthy and therefore unlikely to develop complications, but the evidence for that is mixed. One recent study found that 70 percent of people hospitalized for chickenpox complications were otherwise healthy.

“It’s hard to understand why people would choose to get sick with this,” said Dr. Lisa Asta, an associate clinical professor of pediatrics at the University of California at San Francisco.

Several parents said their own mild experiences with chickenpox helped convince them that the vaccine was unnecessary.

“I just take into consideration the seriousness of the disease versus the risk of the vaccine,” said Allison Neally, a high school teacher from Algonquin, Ill. Most pox parties resemble an ordinary playdate, with extra measures to aid infection. Many parents encourage the children to share whistles, lollipops or Popsicles. One mom said her kids shared T-shirts with the infected kids.

“It definitely goes against that old momma bear, papa bear, protect-my-child mentality,” said Neally, whose daughter attended a party but failed to catch chickenpox.

Megan Cummins, a shiatsu therapist from Chicago’s Hyde Park neighborhood, said that at one party her children hesitated to share a drink box with the infected toddler, who had a runny nose and was covered in spots.

“My kids were sort of repulsed,” Cummins said. She said her two older children attended three parties but never got infected. She still hopes to get them infected, but said that at times the parties felt awkward.

“Once I realized I was driving to Oak Park from Hyde Park to be at a complete stranger’s house and share their germs – that’s a little weird,” she said.

Some moms said their pediatricians frowned on chickenpox parties, but Edna Navarro-Vidaurre of Chicago said her children’s doctor saw nothing wrong with the idea. She was relieved when her 2-year-old son got the disease after his first party, and then her 5-year-old daughter got infected after three tries.

“I felt I was kind of lucky because I got it done within a few months,” Navarro-Vidaurre said.