Some parents say they are concerned about side effects from the new vaccine _ even though nothing serious has turned up in tests so far _ while others say swine flu doesn't amount to any greater health threat than seasonal flu.
Jackie Shea of Newtown, Conn., the mother of a 5-year-old boy named Emmett, says the vaccine is too new and too untested.
"I will not be first in line in October to get him vaccinated," she said in an interview last month. "We're talking about putting an unknown into him. I can't do that."
The AP poll found that 38 percent of parents said they were unlikely to give permission for their kids to be vaccinated at school.
The belief that the new vaccine could be risky is one federal health officials have been fighting from the start, and they plan an unprecedented system of monitoring for side effects.
They note that swine flu vaccine is made the same way as seasonal flu vaccines that have been used for years. And no scary side effects have turned up in tests on volunteers, including children.
On Wednesday, Health and Human Services Secretary Kathleen Sebelius appealed for widespread inoculation against swine flu, vouching unconditionally for the vaccine: "We know it's safe and secure."
The AP poll, conducted Oct. 1-5, found 72 percent of those surveyed are worried about side effects, although more than half say that wouldn't stop them from getting the vaccine to protect their kids from the new flu.
Giving flu shots to schoolchildren is also an idea many parents are still getting used to. It was only last year that the government recommendation kicked in for virtually all children to get it. Seasonal flu vaccination rates for children last year ranged from about 48 percent for toddlers to about 9 percent for teens.
It traditionally takes a while for parents to learn about and accept a new vaccine and years for immunization rates to grow, said Dr. Matthew Davis, a University of Michigan Medical School associate professor who has overseen polling on flu issues.
Special swine flu vaccination clinics at schools are being planned in many states. Children are the main spreaders of infectious disease, and if large numbers are coming down with swine flu, there are ripple effects for everyone else.
The AP poll found 59 percent are likely to let their kids be vaccinated at school. But the kind of concerns voiced by parents could put a dent in public health efforts.
A survey Davis directed for C.S. Mott Children's Hospital in Michigan suggested one reason for rejecting the vaccine is that about half of parents said they did not consider swine flu any worse than the seasonal bug.
"Basically, the swine flu is the flu. I'm not overly excited about it," said Julie Uehlein, a Tullahoma, Tenn., mother who is against swine flu vaccinations for her 8-year-old son and 3-year-old daughter.
"My concerns about the vaccine are what are the long-term effects," she added.
Some, like Shea, recall the 1976 swine flu immunization campaign that vaccinated 40 million Americans against an epidemic that never materialized. Worse, many who got the shots back then filed injury claims blaming health problems on the vaccine, with some reporting a paralyzing condition called Guillain-Barre syndrome.
Health officials did not find evidence the vaccine caused the condition, noting it occurs naturally anyway and would be bound to show up in such a large group. Many people were unjustifiably blaming all sorts of health problems on the vaccine, some health experts believe.
That's why the government is already trying to educate people about how common many health problems are, and why it's handing out cards telling people how to report any side effects.
Forsome parents, fears are compounded by worries about thimerosal, a mercury-based preservative that will be in roughly 60 percent of the 225 million swine flu doses ordered for Americans.
The preservative is not in the FluMist nasal spray, which can be given to healthy kids age 2 and older. But it's in many injectable doses, which are packaged in multi-dose vials that require thimerosal to prevent bacterial contamination.
Fears that the preservative or something in vaccines themselves can lead to autism remain entrenched in some quarters _ despite no evidence from the most rigorous scientific studies.
Some autism advocacy groups echo parents' concerns about swine flu vaccine, and also argue it's a bad idea to spend so much time and money on the new flu.
"We're flipping out over swine flu, but it's only affected a few thousand people. Why isn't somebody freaking out about the autism epidemic?" said Wendy Fournier, president of the National Autism Association.
Vaccine makers are sensitive to demand for preservative-free shots. Parents can ask their doctors to order preservative-free, single-dose vaccine for their kids, said Dr. Tom Frieden, head of the Centers of Disease Control and Prevention.
As for his own two school-age children, Frieden said in a recent interview: "I would have no hesitation about getting my kids vaccinated by thimerosal-containing vaccines."
Health officials and many parents are strong believers in the vaccine, and warn about the potential dangers of a virus that has caused at least 9,000 U.S. hospitalizations and at least 600 deaths, including 60 children.
Jennifer Barnes enrolled herself and her two children in one of the government studies of the new vaccine, seizing an opportunity to get them all immunized before the illness became widespread.
"I thought, 'This is an opportunity to get the kids vaccinated, and I better jump on it,'" said Barnes, 32, a speech language pathologist who lives in Decatur, Ga.
Barnes said she gets her kids vaccinated against flu each year not only for their own health but to protect others. "My kids hang around kids who might have lowered immune systems. I would hate for them to get something and pass it on," she said.
Shea said she appreciates those arguments, but she's hesitated to talk about swine flu vaccine with other parents, who seem polarized on the topic. "There's the crunchy granola group" against flu vaccinations, she said, "and the very staunch, follow everything group" who extol them.
She also worries that swine flu could become more widespread and dangerous than it is now. If that happens, she said, she would probably try to get her son vaccinated, though she's aware there are risks in waiting, too.
"It's one of those things where you're almost damned if you do, damned if you don't," she said.
The AP-GfK poll was based on a nationally representative sample of 1,003 adults age 18 or older, contacted by telephone on land lines and cell phones. The margin of sampling error is plus or minus 3.1 percentage points for all adults, 5.2 percentage points for parents.
On the Net:
U.S. government swine flu Web site: http://www.flu.gov