Registered nurse Melody Butler seeks to provide science-based answers to American parents as she urges them to vaccinate their children against Covid-19.

But her efforts to do so on social media through Nurses Who Vaccinate -- a volunteer group she founded -- is up against a deluge of claims that the shots are dangerous.

The claims are designed to evoke fear: a 16-year-old girl said to have been "permanently damaged" by Pfizer-BioNTech's shot. An image of a 17-year-old playing basketball juxtaposed with a photo of a boy hooked up to machines in a hospital after allegedly suffering "blood clots in his brain" following vaccination.

Such claims are nearly impossible to verify without access to private medical records, allowing them to escape content moderation on social media platforms and spread doubt about the safety of vaccination

"A lot of times these stories are being used and the stories are being manipulated by anti-vaccine organizations," Butler told AFP. "Their main goal is to scare people away from vaccinating."

When talking to mothers like herself, Butler says she "will never say that adverse reactions don't happen, because they do happen," but she emphasized that evidence does not point to a high risk of severe side effects from Covid-19 vaccination.

The US Centers for Disease Control and Prevention (CDC) says that children have most commonly reported arm pain or fever following vaccination.

- Personal appeals -

Parents have also been targeted with misleading posts featuring obituary photos of vaccinated teenagers who later died. The posts claim a direct link to the shots, but no such deaths have been confirmed.

CDC spokeswoman Martha Sharan said that officials investigate all reports of serious reactions but cannot comment on individual cases.

The CDC has "not detected any unusual or unexpected patterns for deaths following immunization that would indicate that Covid vaccines are causing or contributing to deaths, outside of the five confirmed deaths following the Janssen vaccine," she said, using another name for the Johnson & Johnson shot.

US regulators recently authorized the Pfizer-BioNTech shot for young children -- the only one of the vaccines currently allowed for this use.

Even when parents acknowledge that vaccination can protect children from severe Covid-19, this can be pushed to the background by claims of vaccine injury, said Tara Kirk Sell, a public health researcher at Johns Hopkins University.

"Science has shown us that those types of efforts at persuasion really work," she said.

Disinformation purveyors know that a personal story will resonate, especially with parents, "because you just think about your child in distress and how terrible that would be."

'Conspiracy narrative'

Texas resident Katie Vitale Pickett, a mother whose children are too young to be vaccinated, is worried about their health -- and about the impact of inaccurate claims circulating online.

"The way the misinformation and anecdotes were shared, like medical fact, was really bothersome... It was presented as on equal footing or standing with sound medical advice from doctors," said Pickett, whose vaccine advocacy led to her being kicked out of a Facebook group for mothers.

Facebook says it regularly removes false claims about Covid-19 and vaccination. It also applies labels affirming that vaccines are monitored for safety, and flags posts that have been fact-checked by independent organizations, including AFP.

But Sell pointed out that "authoritative sources only go so far, and only with a certain population."

A "conspiracy narrative" surrounding the pandemic has turned people away from public health advice, she said, adding: "It's really hard to take apart that narrative, because it's not just one piece of misinformation you have to combat."

Anti-vaccine claims are an online fixture but are now focused on Covid-19, undermining efforts to combat the pandemic.

This was evident in a Kaiser Family Foundation poll from late October that found two-thirds of the parents expressed concern that the vaccine may affect their child's future fertility, despite this claim having been repeatedly debunked.

Stories about alleged negative outcomes from vaccination are much more evocative than those on the success of preventive medicine, said Sell, urging experts to find new ways to talk about public health.

"Health providers always try to provide the numbers, and that's just not convincing to a lot of people. These stories are what's convincing them."