Some time between 6 o'clock Sunday night and early Monday morning, somebody journeyed between Willow Creek and Burnt Ranch spraying blood-red opposition to vaccinations on schools, medical clinics, sidewalks and the K-rails -- concrete barriers -- lining Highway 299.

The Humboldt County Sheriff's Department was still investigating, said Sheriff's Department spokesperson Brenda Godsey on Monday afternoon.

Terry Bray, administrative assistant to the principal at Trinity Valley Elementary School, on Highway 96 in Willow Creek, arrived at work at 7:30 a.m. on Monday to see "SV40" and "VAX waiver" spray-painted in red on the school's outside cafeteria wall, and a skull and crossbones spray-painted on the school's new office sign in front. On the adjacent preschool they'd spray-painted "autism."

At the Willow Creek Community Health Center, on Highway 299, "VAX" and a skull with Xs for eyes were spray-painted on the front of the building, and "SV40" and "autism" spray painted on one side and on the back of the building, all in two- to three-foot high red letters, said receptionist and medical records clerk Kelly Earls.

"It was a surprise," she said.

At Six Rivers Medical Center, on Highway 96, "cancer," "VAX," "SV40" and a skull were spray painted on the front of the building, and "autism" was painted on the sidewalk in front of it.

Burnt Ranch Elementary School, 14 miles up the road in Trinity County, similarly was spray-painted with "VAX," a skull and "VAX waiver." Ironically, on Monday, the school held its first "celebration of character" assembly of the year, said Superintendent Sarah Supahan that evening.

"We emphasize a different character trait each month," Supahan said. "And this month was 'trustworthiness.' So the teacher in charge was asking, 'What does it mean to be trustworthy?' And the students were giving different examples. And then one student said, 'It means not spray-painting your school.'"

Supahan said they're stumped as to who did it. "We haven't had complaints," she said. "There's been no parent concern about vaccinating. Our parents are aware we have a waiver."

The Sheriff's Department's Godsey said Deputy Greg Barry, on his way to investigate the vandalism in Burnt Ranch, discovered the spray-painted K-rails along the way.

"So obviously whoever did this is mobile," Godsey said.

Bray, at Trinity Valley Elementary School, said she figured the graffiti was done by adults "because they spelled everything right."

Bray said she Googled "SV40" to find out what it means. "SV40" stands for "Simian Virus 40" and refers to a tumor-causing virus that was found in monkey kidney cells that were used to create the first polio vaccine. The cells' use was eliminated by 1963, according to the SV40 Cancer Foundation's Web site, but some people believe it was used into the 1990s.

Bray said she didn't know why they'd been targeted. School kids have to get vaccinated for a number of things, including polio, whooping cough, mumps, measles and rubella, but parents can sign a waiver.

At the Willow Creek Community Health Center, RN Clinic Coordinator Erica Dykehouse said her first thought when she saw the graffiti was that perhaps it had been done by the parent or relative of someone who had been recently diagnosed with autism. It isn't known what causes autism, she said. But about 12 years ago the medical journal The Lancet published an article linking the preservative thimerosal in the mumps-measles-rubella vaccine to cases of autism. And although it later was found that the article was based on altered data, and although subsequent studies have debunked the link, the myth persists.

"I wondered why we got hit," Dykehouse said. "We don't force parents to vaccinate their children, and we do explain to them the risks of it, and we do explain to them that even though there's no link between thimerosal and autism, they went ahead and just took it out of vaccines in 2002."

But she said she can sympathize with worried parents. "Just looking at it from a parent's perspective, you are responsible for this other being, and every decision you make on their behalf you're wondering, what are the consequences going to be? ... But then when you look at small pox, or whooping cough ... or polio, you have to weigh that against the risk of being vaccinated."

Humboldt County has a huge pocket of non-immunized children. California Department of Public Health statistics from 2008 reveal that in most elementary schools in the state, 80 to 100 percent of kindergarteners were immunized. An immunization rate above 80 percent provides "herd immunity," said Ann Lindsay, Humboldt County Health Officer, on Tuesday.

"But if fewer are immunized, there's a chance you could get an outbreak of a real serious, preventable disease," she said. "About half of our schools [in Humboldt] have insufficient immunization rates." Several fall below 30 percent. And there have been outbreaks -- two years ago, 67 Humboldt kids got whooping cough and two were air-ambulanced out for intensive care.

Lindsay said she "can't support that kind of 'community education'" that the vandals had engaged in.

Bray, at Trinity Elementary, said even if you're vehemently anti-vaccination, "this is not the way to get your point across."

"Schools are in financial crisis as we speak and we just really don't have the money or the time to have to deal with something like this," Bray said.

As a side note, the character trait for next month's assembly at Burnt Ranch Elementary School is "Respect."