For the folks who think that natural immunity beats a vaccination,Trinidad Elementary School has turned into a textbook lesson on how to grow your own outbreak.

Chickenpox has spread swiftly through the 180-student school, apparently contracted so far by at least 16 children and adults. The numbers aren't surprising given that roughly 20 percent of the students have not been vaccinated, at their parents' request.

Each of those children could be a biological time bomb for someone with AIDS whose immune system is badly compromised, or for a woman in the wrong stage of pregnancy, who could end up with a paralyzed, blind or developmentally disabled baby, according to the Centers for Disease Control.

Is that OK?

Well, the school district is hosting a free vaccine clinic being offered by Humboldt County, but it's not actually recommending that kids get vaccinated.

"We are offering. We are not taking a medical stand," said principal Geoff Proust.

"The parent group we have has a lot of people who have doubts aboutthe safety of vaccines or the honesty of governmental forces" that recommend them, he said. "On one hand, I support the independent thinking of my parent group. On the other hand, they might not necessarily be thinking beyond their own family."

Even in a county with a vocal anti-vaccine contingent, outbreaks like the one in Trinidad apparently aren't common.

Chris Hammond, a communicable disease program nurse for Humboldt County, said this is the first she's seen in her three years here. The county has had no documented episode of a youngster with chickenpox making any other person seriously ill, she said.

There are risks to getting any vaccine. There are also risks to skipping them, risks that reach beyond any one child. A good chickenpox summary is here, from The Children's Hospital of Philadelphia.