WASHINGTON (BLOOMBERG) - The excuses range from the merely false to the absurd. The shots do not work. They impair fertility. They will alter your DNA. They will magnetise you. They actually spread the virus.

Unvaccinated Americans cite a litany of myths to explain their hesitance to get shots, confounding local health officials battling yet another surge of coronavirus cases fuelled by the more transmissible Delta variant. Inside the White House, the concern is so acute that President Joe Biden has publicly lashed out at Facebook for helping to spread disinformation.

"Everything from Bill Gates putting a microchip in it - I've heard everything. It's ridiculous," said Mr Tom Keller, chief executive of Ozarks Health Care in southern Missouri, a region with low vaccination rates that is an epicentre of the US Delta-variant outbreak.

"People are listening to social media instead of listening to their docs," he said. "Somebody who has a million followers all of the sudden becomes the expert on not getting the vaccine."

Just as the Biden administration appeared on the verge of snuffing out Covid-19 in the United States, a shadow pandemic of disinformation threatens to prolong the crisis. Promulgated virus-like itself through social media platforms, a miasma of uncertainties, anecdotes and outright lies has seized the imaginations of Americans hesitant to be vaccinated, slowing the US campaign to inoculate its population.

Mr Biden himself showed his frustration last week, accusing Facebook and other social media giants on Friday of "killing people" by allowing posts with falsehoods about the virus and vaccines.

On Wednesday (July 21), during a town hall hosted by CNN, Mr Biden said that "what we're trying to do is use every avenue we can - public, private, government, non-government - to try to get the facts out, what they really are".

He walked back his remarks about Facebook this week after the company rebuked him in a blog post, citing data showing that its platform has helped to increase vaccination rates and reduce hesitancy among its users.

Mr Biden instead cited a report from the Centre for Countering Digital Hate (CCDH), a non-profit with offices in London and Washington, that found 12 leading anti-vaccine individuals and organisations are responsible for as much as 70 per cent of Facebook content discouraging Covid-19 vaccinations.

"Facebook isn't killing people," Mr Biden said on Monday. "These 12 people who are out there giving misinformation, anyone listening to it is getting hurt by it, it's killing people. It's bad information."

He added that "instead of taking it personally", Facebook should "do something about the misinformation".

Slowing US vaccinations

The campaign against vaccination has contributed to a sharp slowdown in the pace of inoculations since April, forcing the government to shift to what Mr Biden has called a "door-to-door" effort to get shots in arms - a remark that itself has been portrayed as conspiratorial by some Republican leaders.

While more than half the US population overall has received at least one dose of a vaccine, a recent Bloomberg analysis found that among the least-vaccinated counties in the US, the proportion with a shot is only about 28 per cent.

A political divide has also emerged, with Republicans far more likely to be unvaccinated than Democrats, polls show. Conservative media and some Republican office-holders have in some cases amplified disinformation, or have tacitly supported vaccine hesitancy by refusing to get shots themselves - or admit they have.

Several Fox News hosts including Mr Sean Hannity urged their viewers this week to get vaccinated, after criticism that the network's programmes had previously aired segments downplaying the threat of Covid-19 and questioning the necessity and safety of the shots.

The US surgeon-general, Dr Vivek Murthy, issued an advisory on misinformation last week.

"Today, we live in a world where misinformation poses an imminent and insidious threat to our nation's health," he said at a White House briefing.

About 150 leading anti-vaccine online accounts gained more than 10 million social media followers from December 2019 to December last year, especially on Instagram and YouTube, according to CCDH.

Dr Murthy accused large social media companies of practically designing their products to spread misinformation.

"Modern technology companies have enabled misinformation to poison our information environment with little accountability to their users," he said.

"They've allowed people to intentionally spread misinformation, what we call disinformation, to have extraordinary reach. They design product features, such as like buttons, that reward us for sharing emotionally charged content, not accurate content, and their algorithms tend to give us more of what we click on, pulling us deeper and deeper into a well of misinformation."

Mr Biden's chief of staff, Mr Ron Klain, recently called Facebook chief executive Mark Zuckerberg to complain about the social media platform's role in the spread of vaccine misinformation.

"The platforms need to do better, I think particularly Facebook needs to do better," Mr Klain told the New York Times in a podcast released on July 1. "There is just no question that a lot of misinformation about vaccines is coming from postings on Facebook, and this is a life or death situation here."

Facebook said in its blog post on Saturday that more than two billion people worldwide have viewed "authoritative information" on Covid-19 and vaccines using its platform, and that 3.3 million Americans used its vaccine finder tool to locate a vaccination site and make an appointment.

"When we see misinformation about Covid-19 vaccines, we take action against it," Facebook vice-president of integrity Guy Rosen wrote in the post.

He said the company had removed 18 million "instances" of Covid-19 misinformation since the beginning of the pandemic and had labelled and reduced the visibility of 167 million posts that had been "debunked by our network of fact-checking partners".

Partisan divide

Social media posts can reinforce pre-existing doubts about the vaccines. A Kaiser Family Foundation survey of unvaccinated adults published on June 30 found that 53 per cent think the shots are too new and 53 per cent are worried about side effects.

About 43 per cent said they just do not want it, 38 per cent do not trust the government, 38 per cent do not think they need a shot and 26 per cent said they do not trust vaccines in general.

Smaller percentages of people said they did not know where to get a shot or were concerned about missing work or having to pay for the vaccine. It is free for anyone in the US.

Republicans, rural residents, younger people and people of colour are among the most wary of Covid-19 vaccination, but demographics do not easily explain hesitancy - or how to combat it. Two-thirds of Democrats live in homes in which everyone is vaccinated, the Kaiser survey found, while 39 per cent of Republicans live in homes in which no one has got a shot.

"Not everyone is going to be hesitant for the same reasons," said Dr Timothy Callaghan, who studies rural health at Texas A&M University. "The most important thing public health can do right now is first understand the beliefs people have. And then explain what is true and what is not. The last thing you want to do is disregard someone's entire belief."

For many hesitant people, the issue comes down to a fundamental lack of trust, Dr Callaghan said. That means government public health messages are often less powerful than counsel from a trusted friend, relative or community leader.

Another Kaiser survey found that people initially sceptical of the vaccine got shots after seeing friends and family inoculated without side effects, after being pressured by friends or family, or after speaking with their doctors.

But in communities where fewer people are vaccinated overall, there is less encouragement or pressure from peers.

"These people have had the opportunity to vaccinate for months. At this point not vaccinating is deeply ingrained in their beliefs," Dr Callaghan said. Changing people's minds at this point, he said, is "about building trust and building relationships".

Corrosive social media

In those places, social media is having a corrosive effect on the vaccination campaign. The large social networks have been slow to take action against unsubstantiated claims about Covid-19 and the vaccines, and when interventions do happen, they are often half-measures.

Instagram, for instance, banned celebrity vaccine opponent Robert Kennedy Jr in February - but he remains on Facebook, Instagram's parent company, and his organisation is on Instagram, Facebook and YouTube.

In Springfield, the city health department's Facebook account has found itself beating back ridiculous allegations, including that the vaccine itself spreads the virus.

"Honestly, I don't know how to find all of the sources because we don't see them," said Ms Katie Towns, assistant director of the Springfield-Greene County health department, in Missouri. "I don't know how to even get to some of this stuff."

Complicating the situation further, the misinformation spread by vaccine opponents has begun to overlap with that of anti-government conspiracy theorists and figures in the far right, including the QAnon movement.

Misinformation about the effect of coronavirus shots on children has found particular resonance among QAnon adherents, who maintain that prominent Democrats are involved in convoluted conspiracies to traffic children.

Some of the disinformation spread by vaccine opponents is simply odd, like a claim the shots will magnetise patients that is popular on TikTok in particular. In the Midwest and South, regions where hesitancy runs deep, questions circulate about whether the vaccines affect fertility (there is no evidence for it) or alter human DNA (they do not).

Politicians could help, especially if more high-profile Republicans would endorse vaccination, work with local leaders to promote shots and stop spreading misinformation themselves, said Dr Matt Motta, a political science professor at Oklahoma State University in Stillwater.

But in many cases, the absence of politicians might be even more helpful. In Springfield, for example, Ms Towns said one of the city's most successful vaccine clinics was an event held at a fire station - Americans still trust firefighters.

In Alabama, one of the country's least vaccinated states, the state health officer, Dr Scott Harris, said that pharmacists, doctors and religious leaders are some of the best proponents for shots.

"These folks who are struggling with getting vaccinated or are opposed to it... they just have such a low level of trust for everybody - and that includes politicians," he said.