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YouTube users searching for vaccine-related content in Portuguese can end up in a network of antivaccination videos.

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Antivaccine videos slip through YouTube’s advertising policies, new study finds

As COVID-19 vaccines approach the finish line, public health officials around the world are battling waves of vaccine misinformation that could derail efforts to protect their citizens. The video platform YouTube recently pledged to help by removing videos containing COVID-19 misinformation and expanding on earlier efforts to limit recommendations for antivaccination videos. Now, a new study in Brazil suggests YouTube’s moderation policies miss many antivaccination videos in Portuguese.

Vaccine hesitancy is as old as inoculation itself. But it has been on the rise for 2 decades, and last year the World Health Organization listed it as one of 10 threats to global health. In Brazil, where 20 vaccines are offered for free through the country’s National Immunization Program, many are also wary. In 2019, about 13% of 2002 Brazilians said they had missed at least one vaccine or did not vaccinate a child under their care. When asked why, more than half replied with an incorrect statement like, “vaccines have a high chance of causing serious side effects.”

To curb its role in the spread of vaccine misinformation, YouTube in January 2019 began to limit recommendations for videos with harmful, vaccine-related content. In an email to Science, a YouTube spokesperson wrote that the watch time for such videos has decreased more than 70% since. A month later, the company announced it would demonetize videos with antivaccination content following a BuzzFeed report showing ads running before these videos.

A new study suggests it hasn’t quite succeeded, at least in Portuguese. Researchers at the State University of Campinas (UNICAMP) and the University of California, Berkeley, simulated the experience of a YouTube user searching for vaccine-related content in Portuguese. Dayane Machado, a misinformation researcher at UNICAMP, says the team wanted to know which videos YouTube’s recommendation algorithm suggested once viewers finished watching their first video.

In February, the researchers used open-source tools that approximate YouTube’s “up next” feature and searched for “vacina+autismo” (vaccines + autism), running the test three times to generate networks of related videos. Each run spit out 2045 videos on average. The researchers selected those that had “vaccine” in the title, had amassed more than 10,000 views, and were connected to at least two other vaccine-related videos via the recommendation panel. They watched each of the selected videos and checked them for vaccine misinformation.

The efforts uncovered a network of 52 videos in 20 channels containing vaccine misinformation in Portuguese, they reported last week in Frontiers in Communication. One-quarter of the videos were preceded by ads, despite YouTube’s demonetization policy. The most common contained misinformation related to vaccine safety and vaccine alternatives. Some videos linked the use of vaccines to “population control” and other conspiracy theories. Nearly half called on viewers to do their own research and use freedom of choice to protect themselves from malevolent actors.

Machado knows of no similar studies into English-language content (though some advocacy groups say they have uncovered such content). Vaccine misinformation videos may still be available in other languages; according to another study out this year, for example, 72% of the most viewed French-language videos about vaccines had antivaccine stances. Such content often grabs people’s interest: Two papers from Italy found that negative videos about vaccines had higher levels of engagement—likes, dislikes, comments and shares—than pro-vaccine videos.

One of the difficulties of monitoring antivaccination videos, Machado says, is that their content isn’t always explicit, allowing them to slip by moderation tools. “We need human moderators,” Machado says.

A spokesperson for YouTube wrote to Science in an email that the company does have human reviewers for content in languages including Portuguese, and that its policies are enforced globally. Links to six monetized videos in the study were sent to YouTube for review. In a follow-up email, a YouTube spokesperson wrote that the videos did not violate the platform’s Community Guidelines, but that a handful violated their monetization policies, and ads were removed.

Meanwhile, it isn’t getting any easier for public health officials to combat vaccine misinformation. Brazilian President Jair Bolsonaro, for instance, has repeatedly stressed that COVID-19 vaccines won’t be compulsory. The messages may reinforce the notion that vaccines aren’t safe and could “create a problem” says public health researcher Kenneth Camargo of Rio de Janeiro State University, Rio de Janeiro. And antivaccine proponents are taking advantage of the president’s comments. “Every time there’s a political discussion about vaccination … fake news is ready to go,” says Isabella Ballalai, vice president of the Brazilian Immunization Society. “They’re very good at this. We need to be as good as them.”