Since the World Health Organization declared the novel coronavirus an international health emergency in January, Facebook Inc has removed more than 7 million pieces of content with false claims about the virus that could pose an immediate health risk to people who believe them.The social media giant, which has long been under fire from lawmakers over how it handles misinformation on its platforms, said it had in recent months banned such claims as 'social distancing does not work' because they pose a risk of 'imminent' harm. Under these rules, Facebook took down a video post on Wednesday by US President Donald Trump in which he claimed that children are "almost immune" to COVID-19. But in most instances, Facebook does not remove misinformation about the new COVID-19 vaccines that are still under development, according to the company's vaccine policy lead Jason Hirsch, on the grounds that such claims do not meet its imminent harm threshold. Hirsch told Reuters the company is "grappling" with the dilemma of how to police claims about new vaccines that are as yet unproven."There's a ceiling to how much we can do until the facts on the ground become more concrete," Hirsch said in an interview with Reuters, talking publicly for the first time about how the company is trying to approach the coronavirus vaccine issue.Tom Phillips, editor at one of Facebook’s fact-checking partners Full Fact, sees the conundrum this way: “How do you fact check about a vaccine that does not exist yet?”For now, misinformation ranging from unfounded claims to complex conspiracy theories about the developmental vaccines is proliferating on a platform with more than 2.6 billion monthly active users, a review of posts by Reuters, Facebook fact-checkers and other researchers found.The worry, public health experts told Reuters, is that the spread of misinformation on social media could discourage people from eventually taking the vaccine, seen as the best chance to stem a pandemic that has infected millions and killed hundreds of thousands worldwide, including 158,000 people in the United States alone.At the same time, free speech advocates fret about increased censorship during a time of uncertainty and the lasting repercussions long after the virus is tamed.Drawing the line between true and false is also more complex for the new COVID-19 vaccines, fact-checkers told Reuters, than with content about vaccines with an established safety record.Facebook representatives said the company has been consulting with about 50 experts in public health, vaccines, and free expression on how to shape its response to claims about the new COVID-19 vaccines.Even though the first vaccines aren’t expected to go to market for months, polls show that many Americans are already concerned about taking a new COVID-19 vaccine, which is being developed at a record pace. Some 28% of Americans say they are not interested in getting the vaccine, according to a Reuters/Ipsos poll conducted between July 15-21. Among them, more than 50% said they were nervous about the speed of development. More than a third said they did not trust the people behind the vaccine's development.The UK-based non-profit Center for Countering Digital Hate reported in July that anti-vaccination content is flourishing on social media sites. Facebook groups and pages accounted for more than half of the total anti-vaccine following across all the social media platforms studied by the CCDH.One public Facebook group called "REFUSE CORONA V@X AND SCREW BILL GATES," referring to the billionaire whose foundation is helping to fund the development of vaccines, was started in April by Michael Schneider, a 42-year-old city contractor in Waukesha, Wisconsin. The group grew to 14,000 members in under four months. It was one of more than a dozen created in the last few months which were dedicated to opposing the COVID-19 vaccine and the idea that it might be mandated by governments, Reuters found.Schneider told Reuters he is suspicious of the COVID-19 vaccine because he thinks it is being developed too fast to be safe. "I think a lot of people are freaking out," he said.Posts about the COVID-19 vaccine that have been labeled on Facebook as containing "false information" but not removed include one by Schneider linking to a YouTube video that claimed the COVID-19 vaccine will alter people’s DNA, and a post that claimed the vaccine would give people coronavirus. Facebook said that these posts did not violate its policies related to imminent harm. "If we simply removed all conspiracy theories and hoaxes, they would exist elsewhere on the internet and broader social media ecosystem. This helps give more context when these hoaxes appear elsewhere," a spokeswoman said.Facebook does not label or remove posts or ads that express opposition to vaccines if they do not contain false claims. Hirsch said Facebook believes users should be able to express such personal views and that more aggressive censorship of anti-vaccine views could also push people hesitant about vaccines towards the anti-vaccine camp.‘IT’S KIND OF ON STEROIDS’At the crux of Facebook’s decisions over what it removes are two considerations, Hirsch said. If a post is identified as containing simply false information, it will be labeled and Facebook can reduce its reach by limiting how many people will be shown the post. For example, it took this approach with the video Schneider posted suggesting the COVID-19 vaccine could alter people’s DNA.If the false information is likely to cause imminent harm, then it will be removed altogether. Last month, under these rules, the company removed a video touting hydroxychloroquine as a coronavirus cure – though only after it racked up millions of views.In March 2019, Facebook said it would start reducing the rankings and search recommendations of groups and pages spreading misinformation about any vaccines. Facebook’s algorithms also lift up links to organizations like the WHO when people search for vaccine information on the platform.Some public health experts want Facebook to lower their removal standards when considering false claims about the future COVID-19 vaccines. "I think there is a duty (by) platforms like that to ensure that they are removing anything that could lead to harm,” said Rupali Limaye, a social scientist at the Johns Hopkins Bloomberg School of Public Health, who has been in talks with Facebook. "Because it is such a deadly virus, I think it shouldn’t just have to be 'imminent.'"But Jacob Mchangama, the executive director of Copenhagen-based think tank Justitia who was consulted by Facebook about its vaccine approach, fears the fallout from mass deletions: "This may have long-term consequences for free speech when this virus is hopefully contained," he said.Misinformation about other vaccines has rarely met Facebook's threshold for risking imminent harm.However, in Pakistan last year, the company intervened to take down false claims about the polio vaccine drive that were leading to violence against health workers. In the Pacific island state of Samoa, Facebook deleted vaccine misinformation because the low vaccination rate was exacerbating a dangerous measles outbreak.“With regard to vaccines, it's not a theoretical line … we do try to determine when there is likely going to be imminent harm resulting from misinformation and we try to act in those situations,” Hirsch told Reuters.To combat misinformation that doesn’t meet its removal criteria, Facebook pays outside fact-checkers – including a Reuters unit – who can rate posts as false and attach an explanation. The company has said that 95 percent of the time, people who saw fact-checkers' warning labels did not click through to the content. Still, the fact-checking program has been criticized by some researchers as an inadequate response to the amount and speed of viral misinformation on the platforms. Fact-checkers also do not rate politicians' posts and they do not judge posts that are exclusively in private or hidden groups.Determining what constitutes a false claim regarding the COVID-19 shot is much harder than fact-checking a claim about an established vaccine with a proven safety record, Facebook fact-checkers told Reuters."There is a lot of content that we see and we don't even know what to do with it," echoed Emmanuel Vincent, founder of Science Feedback, another Facebook fact-checking partner, who said the number of vaccines in development made it difficult to debunk claims about how a shot would work.In a study published in May in the journal Nature, physicist Neil Johnson's research group found that there were nearly three times as many active anti-vaccination groups on Facebook as pro-vaccination groups during a global measles outbreak from February to October 2019, and they were faster growing.Since the study was published, anti-vaccine views and COVID-19 vaccine conspiracies have flourished on the platform, Johnson said, adding, "It's kind of on steroids."