Before the chickenpox vaccine was introduced more than 20 years ago, parents regularly exposed their kids to the virus to build an immunity.
Today, some parents refuse to vaccinate their children because they're worried about the very rare side effects.
Alternatively, some of those parents are organizing "pox parties" on Facebook, in which they bring their healthy kids in contact with a child who has chickenpox.
Parents in these groups are willing to drive hours and even to different states to put their kids in the same room as an infected person.
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In the Denver area, KUSA found parents who share strategies for best spreading the infection, including "tenting," or sharing a small, enclosed space with an infected child who has exhaled into the air for 20-30 minutes.
"Then let the party begin!" one Facebook post read.
But biologists say "not so fast."
“There’s this emphasis on natural immunity being better than vaccine-delivered immunity. So, the idea [is] that you would get your child chickenpox, and that would give them this sort of life-long immunity,” Lindsay Diamond, who holds a doctorate in molecular biology and co-founded Community Immunity told KUSA-TV. “But you can achieve the same thing, or close to, with the vaccine without serious risks.”
The Colorado Department of Health is reminding parents chickenpox can be a serious infection, especially for infants, pregnant women and people with weakened immune systems. They recommend children get vaccinated.