Two-thirds of anti-vaccination propaganda posted online is created by just 12 so-called influencers, research has found.

Different to those who describe themselves vaccine hesitant, anti-vaxxers tend to employ aggressive methods to persuade others not to get injections designed to help prevent disease.

The list was compiled by the Centre for Countering Digital Hate (CCDH) and found most of the figures, who claim to be political or medical leaders, are based in America.

After social media companies were made aware of the prevalence of the material some was removed, but many videos and articles remain online today.

Critics believe some are exploiting loopholes which mean that if they post content under another name or appear on a page hosted by another user their anti-vax content is not removed.

Imran Ahmed, the chief executive of the CCDH, told Sky News that social media giants “bear none of the cost for the content” they host, including dangerous material which can drive users to their platforms.

He called on the companies to do more to remove it quickly, amid fears that those left unvaccinated remained more vulnerable to COVID-19 infection and, crucially, hospitalisation.

He said the most effective anti-vaxxers were “great marketers” and drew people in by generating content related to wellness or fertility, then gradually linked these issues to vaccination.

Mr Ahmed said the algorithms used by social media platforms then fed people more and more similar content, until they see it frequently while online – thus normalising the opinions.

“All the platforms care about is content that people will spend time on so they can serve them adverts at the same time… they are reluctant to take any credible action,” he said.

Ed Stubbs, a teacher who developed a package of lessons designed to tackle vaccine hesitancy in schools, said that because young people spent so much time online they could easily find themselves watching a lot of anti-vax content.

He warned that fear over the COVID-19 vaccine programme had fed into fears about other vaccines administered to young people as a matter of course in schools and prompted growing general hesitancy to getting vaccinated for anything.

“Young people obviously look on social media, they see quite a lot of jokes on Instagram and Tik Tok, things like ‘I got my vaccine and then this happened to me’,” he said.

“They are jokes and the students would even tell me and be laughing while they say them, but it still has an effect on them and instead of vaccines being something quite dull, boring, and necessary, it’s something that is controversial, weird and slightly alarming.”

Mr Stubbs added that labelling people who are vaccine hesitant as anti-vaxxers can be dangerous, especially in schools, as it drives discussion underground and gives teachers less opportunity to open up conversations which could encourage uptake.

But he also warned that teachers must be prepared to be unequivocal about the benefits of getting vaccine and not sit on the fence, because they are in a position of trust.

Chris Philp, a minister in the department for digital, culture, media and sport, said the government would legislate for fines and other action to force social media companies to remove content deemed damaging but admitted that policing the internet was not an easy task.

“The internet is a large space and there is definitely more to do and we are determined to make sure that with social media firms, we take the action necessary,” he said.

“There’s always more to do. And in fact, in the coming months, we’re going to be introducing a piece of legislation, the online safety bill, to go even further in imposing statutory legal duties on social media firms to make sure they act in this area.”