Another hallmark of conspiracy theorists: rage. "By analysing the language used in hundreds of thousands of tweets from the most popular conspiracy theorists on Twitter, we found that they express much more negative emotions -- particularly anger -- compared to their popular science counterparts," writes van der Linden, a psychologist at the University of Cambridge.

In their analysis of language patterns among conspiracy theorists, his team also found that they tended to "talk much more about other groups and power structures," and they used swear words more often than the comparison group.

Van der Linden proposes that misinformation and conspiracy theories represent "viruses of the mind" that can latch onto the brain and hijack its "basic cognitive machinery." Like other viruses, misinformation spreads via contact with other infected people, but van der Linden asserts that it can be stopped with a "psychological vaccine" -- one that "does not require any needles, just an open mind."

According to van der Linden, the idea that it might be possible to deliver a cognitive vaccine against propaganda was first proposed decades ago by psychologist William J. McGuire, whose research laid the groundwork, van der Linden says, for the concept of "prebunking." McGuire hypothesized that if you gave people detailed warning about the kind of propaganda they would encounter before they were exposed to it, they would be more likely to view it as misinformation and less prone to accept it. McGuire published a summary of his findings in 1970 in a Psychology Today article titled "A Vaccine for Brainwash."

McGuire died in 2007, but van der Linden and his colleagues have built upon his work in numerous experiments. One of these tested a tool that van der Linden's team created to train people to spot misinformation. "Bad News" is an online game that gives players a chance to become nefarious producers of fake news. The game allows players to try out the "six degrees of manipulation" -- techniques that van der Linden's group has identified as hallmarks of misinformation. These include discrediting ("a technique that deflects attention away from accusations by attacking the source of the criticism"); deliberately playing on emotions like fear and moral outrage to get people riled up; provoking polarization; posing as experts or legitimate news outlets; promoting conspiracies; and trolling.

The researchers tested players' ability to spot fake news before and after they'd taken part in the game, and in a dataset of 15,000 trials, they found that "everyone improved their ability to spot misinformation after playing the game," van der Linden writes. People who'd fared worst at spotting fake news in the pre-game quiz made the biggest improvements. But the improvements were modest: "On average, players adjusted their ranking of fake headlines downwards by about half a point (0.5) on the 1-7 reliability scale after playing."

In another experiment, van der Linden's team exposed volunteers to a specific set of real-world misinformation about global warming, but forewarned them that "some politically motivated groups use misleading tactics" to suggest that climate scientists disagree about the causes of climate change (when in fact the vast majority agree humans are to blame). The researchers found that this warning made volunteers less vulnerable to accepting climate misinformation. People exposed to two prebunking scenarios updated their estimates of the scientific consensus on human-caused climate change by about 6.5 to 13 percentage points, with the more detailed forewarning producing the biggest improvements. And the findings held regardless of the volunteers' initial attitudes. "We were not just preaching to the converted," he writes.

Van der Linden makes the case that it's possible to inoculate people against misinformation, but if there's one lesson that's come from the Covid-19 pandemic, it's that developing a vaccine is one thing; convincing people to take it presents a whole other challenge.