An open letter urging Spotify to crack down on COVID-19 misinformation has gained the signatures of more than a thousand doctors, scientists and health professionals spurred by growing concerns over anti-vaccine rhetoric on the audio app's hit podcast, The Joe Rogan Experience.

The medical and scientific experts slammed Rogan's track record of airing false claims about the coronavirus pandemic, vaccines and unproven treatments, calling it "a sociological issue of devastating proportions." Spotify, they say, has enabled him.

While audio apps so far have escaped the scrutiny that has befallen social media platforms such as Facebook and Twitter, the pressure on Spotify illustrates how podcasts have emerged as an influential source of misinformation.

In a December episode of his podcast, Rogan interviewed Dr. Robert Malone, a scientist who worked on early research into the mRNA technology behind top COVID-19 vaccines, but who is now critical of the mRNA vaccines.

Malone made baseless and disproven claims, including falsely stating that getting vaccinated puts people who already have had COVID-19 at higher risk.

The episode immediately raised alarm bells for Katrine Wallace, an epidemiologist at the University of Illinois Chicago's School of Public Health, who signed the letter. She is part of a community of experts who debunk medical misinformation on social media, and she says she received hundreds of messages from followers about Rogan's Malone interview.

"Their friends and family were sending it to them as evidence that the vaccines are dangerous and that they shouldn't get it," she said. "It provides a sense of false balance, like there's two sides to the scientific evidence when, really, there is not. The overwhelming evidence is that the vaccines are safe and that they're effective."

Rogan's reach worries health experts

Wallace was particularly worried because Rogan, a stand-up comedian and TV personality, has such a big audience. While Spotify does not disclose how many people listen, his show ranked as the platform's most popular podcast globally for the last two years. And he's worth a lot to the company: In 2020, he signed an exclusive licensing deal with Spotify reportedly worth $100 million.

"We are in a global health emergency, and streaming platforms like Spotify that provide content to the public have a responsibility not to add to the problem," Wallace said.

It wasn't the first time Rogan or his guests have floated dubious or outright false information about the pandemic. He has claimed young and healthy people don't need COVID-19 vaccines. He has promoted taking ivermectin as a treatment, which the Food and Drug Administration has warned against.

Wallace and the other letter signers are not asking Spotify to kick Rogan off its platform. But they want the company to be more transparent about its rules, do more to moderate misinformation and make it easier to flag these kinds of baseless claims.

Spotify declined to comment to NPR. It has previously said it bans "dangerous false, deceptive, or misleading content about COVID-19 that may cause offline harm and/or pose a direct threat to public health."

The company says it has taken down 20,000 podcast episodes for breaking that policy since the start of the pandemic. It has also taken down other episodes of Rogan's show, including an interview with conspiracy theorist Alex Jones. But Rogan's Malone interview is still available.

Last year, Spotify CEO Daniel Ek told Axios that the company does not take responsibility for what Rogan or his guests say. He compared the podcaster to "really well-paid rappers" on Spotify, saying, "We don't dictate what they're putting in their songs, either."

Rogan did not respond to NPR's request for comment.

Researchers say scrutiny of podcasts is overdue

Misinformation researchers say it was only a matter of time until the spotlight turned to podcasts.

"Wherever you have users generating content, you're going to have all of the same content moderation issues and controversies that you have in any other space," said Evelyn Douek, a research fellow at Columbia University's Knight First Amendment Institute.

So why haven't podcasts gotten the same kind of attention as social networks?

For one thing, it's a fragmented medium. Podcasts exist across lots of different platforms and apps.

Douek says it's also harder to ferret out falsehoods and hate speech in podcasts compared with posts written on Facebook and Twitter.

But audio can be a powerful way to spread misinformation because of all the qualities that make the format so compelling to listeners, said Valerie Wirtschafter, a senior data analyst at the Brookings Institution.

"The podcaster is in your ear," she said. "It's a really unique relationship in that respect, and so the podcaster gains a level of authority and a level of credibility among listeners."

Wirtschafter says as more people become aware of how misinformation spreads online, audio deserves the same scrutiny as social media.

She has studied how the "Big Lie" that the 2020 presidential election was stolen from Donald Trump spread on political podcasts in the lead-up to the insurrection at the U.S. Capitol. She found that half the episodes of the most popular shows released between Election Day and Jan. 6, 2021, contained misleading or false claims about voter fraud and election integrity.

"We're not talking about fringe ideas," she said. "These are the most popular podcasts in the United States."

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