It's flu season, a time when health authorities loudly advise getting a flu shot (even if, yes, this year's shot may be somewhat less effective than in other years). But unfortunately -- as with all things vaccine related -- it's also the season for misinformation, especially among the subset of the U.S. public that is worried about vaccines or that, erroneously, believes them to be somehow dangerous.

In particular, one myth about the flu vaccine -- widely enough held that the FDA and CDC have tried to directly debunk it -- is that you can actually get the flu from getting the shot. The reality, of course, is that the shot contains viruses that have been inactivated and can't make you sick. Nonetheless, the prevalence of this false belief may partly explain why flu vaccine rates are quite low -- only about 42 percent among U.S. adults.

So what do you do to rid people's heads of myths like these, and get them to vaccinate? Unfortunately, suggests a new study, telling them the straight up facts may not work -- it may even backfire.

The new study is by Dartmouth's Brendan Nyhan and the University of Exeter's Jason Reifler, two longtime scholarly chroniclers of people's irrationality when it comes to accepting facts that challenge their belief systems -- a phenomenon that is pervasive in public debates about science, health, the environment, and much more. Nyhan and Reifler have previously documented a so-called "backfire effect" in studies of conservative views about George W. Bush's tax cuts and the Iraq war -- where providing a factual correction of false statements attributed to Bush in a newspaper article led conservatives to believe them more strongly afterwards . Moreover, in a study last year, they similarly showed that a variety of pro-vaccine messages not only failed to sway opponents of vaccinations, but some messages actually decreased their intent to vaccinate or made their wrong beliefs worse.

Now, in their new study in the journal Vaccine, Nyhan and Reifler present test subjects with messages about the flu vaccine. One message (based on language from the CDC) directly debunked the idea that the vaccine can give you the flu. Another message (also based on CDC language) simply described how dangerous the flu can be. Finally, there was a control group, in which subjects didn't hear a message about the flu at all, but were simply asked (as were all participants) about their views on how risky vaccines are, whether the flu vaccine can cause you to get sick, and whether they intended to get a flu shot.

There was some bad news right off the bat: Fully 43 percent of people believed that getting the flu vaccine can actually cause you to get the flu. When it came to hearing a correction of this myth, though, results were a little better: The correction did seem to make people less likely to believe the myth about the dangers of the vaccine -- and even did so among those research subjects who were most fearful of vaccine side effects in general.

However, when the researchers then examined subjects' likeliness to vaccinate themselves against the flu, they found -- disturbingly -- that among these vaccine fearful individuals, hearing a debunking of flu vaccine risks actually led to them being less likely to say they planned on getting the flu vaccine. That's right -- the CDC's language was "actually counterproductive among the group that we’d be most concerned about from a public health perspective, which is the people who are most hesitant about vaccines," explains Dartmouth's Nyhan.

Here's a figure from the study, showing this effect -- the vaccine hesitant people are on the right ("High side effects concern"), and the "Correction" group is the one in which subjects heard the flu vaccine myth actively debunked:

In sum, it looks like yet another backfire effect!

So –what’s up with this? Or more precisely, how can vaccine skeptics simultaneously be swayed by good and accurate pro-vaccine information, and yet simultaneously become less likely to get vaccinated? The result, says Nyhan, suggests that factual misperceptions about vaccines -- like the myth that the flu vaccine causes the flu --"are more a consequence of people’s mixed or negative attitudes towards vaccines, rather than the cause. So when we challenge one misperception, people may simply bring to mind other misconceptions or concerns that they have, and remind themselves of their more general concern about vaccines in the first place."

In light of recent revelations that the flu vaccine may be less effective than usual this season, public health authorities already have their hands full trying to explain why people should, nonetheless, go out and get a flu shot. The latest research suggests they're not going to get a lot of help from the human mind.