Oct. 22, 2009 -- Nearly four in 10 parents do not plan to have their children get the swine flu vaccine this year, with doubts about its safety overwhelmingly cited as the chief reason, underscoring safety concerns as potentially a major impediment to vaccination efforts.

Other results in the latest ABC News/Washington Post poll buttress the point: Three in 10 adults are not confident the vaccine is safe (including one in three parents), and 22 percent believe it's "very" safe. These attitudes heavily influence intentions to get vaccinated, with views of the vaccine's safety a stronger factor than the perceived risk of getting the flu itself.

Click here for PDF with charts and questionnaire.

Even though concern about catching the flu has risen sharply since August, only 35 percent of adults plan to get vaccinated (including 2 percent who say they've already done so); 62 percent say they probably will not get vaccinated. More parents, 56 percent, intend to have their children vaccinated (including 4 percent who say they've done so), but even among parents, 39 percent say they probably won't.

WHY NOT? – This poll asked those parents, open-endedly, why they don't plan to have their children vaccinated, a robust approach because it doesn't prompt for predetermined answers. Far surpassing other mentions, 53 percent in this group raised safety concerns, citing worry about side effects or doubts whether the vaccine's been sufficiently tested.

Far behind that reason, 18 percent of parents who intend not to have their children vaccinated said they're not worried about the flu or don't believe getting the vaccine is worth the trouble; 15 percent said they don't believe the illness is serious enough; 3 percent were unsure about the vaccine's availability; and 1 percent were unsure about its cost. The rest gave scattered other answers.

Swine Flu Vaccine: Parents and Kids

The outcome's similar when comparing views of the vaccine's safety with the intention to get vaccinated. Among parents who are very or somewhat confident the vaccine is safe, 72 percent plan to get their children vaccinated. By contrast, among those who suspect it may not be safe -- again, one in every three parents -- only 13 percent plan to get vaccinations for their kids.

Safety concerns likewise influence personal intentions. Among people who are very confident about the vaccine's safety, 60 percent plan to get it themselves. Among those who are "somewhat" confident, this drops to 40 percent. Among those less confident than that, a mere 6 percent plan to get vaccinated against the swine flu.

Worry about getting the flu, naturally, pushes intention to get vaccinated in the other direction -- up -- but less strongly. In a statistical model testing these relationships, concern over vaccine safety and concern about getting the flu both independently predict intention to get vaccinated, but concern over vaccine safety does so with nearly twice the predictive power.

These results suggest that encouraging vaccinations depends not merely on warning people about getting the flu but as much on persuading doubters that the vaccine is safe.

It should be noted that vaccination intention is naturally based on current information -- how extensive and how serious people perceive the flu to be, what they've heard about the safety of the vaccine and the need to get it, its availability and more. If and when these change, intention to get vaccinated may well move too. (The ABC/Post poll in August, for instance, found a sharp rise in intention to get vaccinated if people's doctors recommended that they do so.)

CONCERN and RESPONSE – As noted, concerns about getting the flu are up; 52 percent in this poll are very or somewhat worried they themselves or someone in their immediate family will get the swine flu, up from 39 percent in August. Many less, though, 21 percent, say this is something that worries them "a great deal," possibly reflecting a sense (or hope) that, if contracted, the flu might be mild.

Concern, Vaccine Safety and Plans to Vaccinate

Concern is higher than for two previous incidents: In March 2006, 41 percent were concerned about catching bird flu; in April 2003, 38 percent expressed worry about getting severe acute respiratory syndrome, or SARS. Worry about swine flu is considerably higher.

Among people who are very concerned about someone in their family contracting swine flu, 50 percent plan to get vaccinated; this declines to 34 percent of those who are somewhat worried, about a quarter of those who are not too worried and a fifth of those who aren't worried at all. There's less of a relationship, though, between worry about contracting the flu and parents' intentions to get their children vaccinated.

In another factor, faith in the ability of the federal government and local hospitals and health agencies to deal with an outbreak of swine flu remains high -- 69 and 79 percent are they're confident in these entities, respectively, although much less are "very confident."

People who are confident in federal and local authorities also are somewhat likelier to plan to get vaccinated, because they're also more confident in the safety of the vaccine.

GROUPS – There are some differences across groups, with plans to get vaccinated higher among older adults (despite the government's advice that younger people are at greater risk), and higher among better-educated adults; 51 percent with post-graduate educations plan to get vaccinated (or have done so) versus 32 percent of those with less formal schooling. One reason, again: Post-graduates are more apt to think the vaccine is safe.

Worry about someone in the household getting swine flu is 11 points higher among parents of children under 18 than among those with no kids at home. Also, women are 17 points more apt than men to worry that they or someone at home may get swine flu, 60 percent versus. 43 percent. Women are a bit more likely than men to plan to get vaccinated, but just slightly so, because they're also 8 points less apt to be confident that the vaccine is safe.

METHODOLOGY – This ABC News/Washington Post poll was conducted by telephone Oct. 15-18, 2009, among a random national sample of 1,004 adults, including landline and cell-phone-only respondents. Results for the full sample have a 3.5-point error margin. Click here for a detailed description of sampling error. Sampling, data collection and tabulation by TNS of Horsham, Pa.