Researchers have found just 12 people are responsible for the bulk of the misleading claims and outright lies about COVID-19 vaccines that proliferate on Facebook, Instagram and Twitter.

"The 'Disinformation Dozen' produce 65% of the shares of anti-vaccine misinformation on social media platforms," said Imran Ahmed, chief executive officer of the Center for Countering Digital Hate, which identified the accounts.

Now the vaccine rollout is reaching a critical stage in which most adults who want the vaccine have gotten it, but many others are holding out, these 12 influential social media users stand to have an outsize impact on the outcome.

After this story published on Thursday, Facebook said it had taken down more of the accounts run by these 12 individuals.

These figures are well-known to both researchers and the social networks. They include anti-vaccine activists, alternative health entrepreneurs and physicians. Some of them run multiple accounts across the different platforms. They often promote "natural health." Some even sell supplements and books.

Many of the messages about the COVID-19 vaccines being widely spread online mirror what's been said in the past about other vaccines by peddlers of health misinformation.

"It's almost like conspiracy theory Mad Libs. They just inserted the new claims," said John Gregory, deputy health editor at NewsGuard, which rates the credibility of news sites and has done its own tracking of COVID-19 and vaccine misinformation "superspreaders."

The claims from the "Disinformation Dozen" range from "denying that COVID exists, claiming that false cures are in fact the way to solve COVID and not vaccination, decrying vaccines and decrying doctors as being in some way venal or motivated by other factors when they recommend vaccines," Ahmed said.

Many of the 12, he said, have been spreading scientifically disproven medical claims and conspiracies for years.

Which provokes the question: Why have social media platforms only recently begun cracking down on their falsehoods?

Both members of Congress and state attorneys general have urged Facebook and Twitter to ban the "Disinformation Dozen."

"Getting Americans vaccinated is critical to putting this pandemic behind us. Vaccine disinformation spread online has deadly consequences, which is why I have called on social media platforms to take action against the accounts propagating the majority of these lies," Sen. Amy Klobuchar, D-Minn., told NPR.

Social networks crack down on COVID-19 vaccine claims

The companies have stopped short of taking all 12 figures offline entirely, but they have stepped up their fight: They've labeled misleading posts. They've removed falsehoods. In some cases, they've banned people who repeatedly share debunked claims.

After NPR's reporting, Facebook said it had taken additional action against some of the figures identified by the Center for Countering Digital Hate, several of which operate multiple accounts on the social network's apps. The company said on Thursday it had found new posts violating its rules.

Facebook has now removed 16 accounts from Facebook or Instagram and placed restrictions on 22 others, such as preventing them from being recommended to other users, reducing the reach of their posts and blocking them from promoting themselves through paid ads.

"We reacted early and aggressively to the COVID-19 pandemic by working with health experts to update our misinformation policy to target harmful claims about COVID-19 and vaccines, including taking action against some of the accounts in the CCDH report," spokesperson Kevin McAlister said in a statement. "In total, we've removed more than 16 million pieces of content which violate our policies and we continue to work with health experts to regularly update these policies as new facts and trends emerge."

However, Facebook also disputed the methodology of the center's report, saying it was not clear what criteria the group used to choose the set of social media posts at which it looked.

Twitter said it permanently suspended two of the "Disinformation Dozen" accounts for repeatedly breaking its rules, required other accounts to delete some tweets and applied labels that link to credible information about vaccines and don't allow the tweets to be shared or replied to. Overall, it's removed more than 22,400 tweets for violating its COVID-19 policies.

However, spokesperson Elizabeth Busby said Twitter distinguishes between "harmful vaccine misinformation that contradicts credible public health information, which is prohibited under our policy, and negative vaccine sentiment that is a matter of opinion."

And so the "Disinformation Dozen" are still easy to find on social media.

"Tried and true" tactics

Sometimes they skirt the platforms' rules by using codes.