An international pressure group that spread false and conspiratorial claims about Covid-19 more than doubled the average number of interactions it got on Facebook in the first six months of 2021 in spite of renewed efforts to curb misinformation on the platform, according to a report.

Pages owned by the World Doctors Alliance – a group of current and former medical professionals and academics from seven countries – received 617,000 interactions in June 2021, up from 255,000 in January, according to a six-month rolling average.

The figures are revealed in a report by the Institute for Strategic Dialogue, which raises fresh questions for Facebook after the whistleblower Frances Haugen claimed that the company knew its products were damaging the mental health of teenage girls and fanning the flames of ethnic violence in Ethiopia.

The World Doctors Alliance includes prominent members who have falsely claimed Covid-19 is a hoax and that vaccines cause widespread harm. Researchers found members “used their qualifications to lend a veneer of credibility to claims that have been proven to be false and often dangerous”.

Imran Ahmed, the chief executive of the Center for Countering Digital Hate, said: “Facebook’s attempts to control the epidemic of misleading information on its platforms are nothing more than performative PR exercises.

“It has had more than a decade to get a handle on the rampant misinformation which has flooded its platforms. But the systems in place fall a long way short of the mark, as this research clearly demonstrates.

“With each new revelation of Facebook’s institutional failure to act, we move closer to social media’s so-called ‘big tobacco moment’, when it is forced to finally take responsibility for the demonstrable harms caused by their products.”

In March 2020, the World Doctors Alliance had a combined following on Facebook of about 4,000 users. This had increased to more than 460,000 by June this year. The increase was mostly driven by the two most prominent members of the group: Dr Dolores Cahill, a former professor at University College Dublin, and Dr Scott Jensen, a former state senator from Minnesota.

Jensen drew international attention after he said extra payments for Covid patients created an incentive for doctors to inflate patient numbers, despite no evidence of fraudulent reporting, according to a USA Today factcheck. Donald Trump then amplified this claim on the campaign trail in 2020.

Cahill, who until March was the chairperson of the rightwing Eurosceptic Irish Freedom party, has claimed Covid-19 vaccines will cause widespread harm and death. Cahill has also claimed that masks and social distancing measures are unnecessary because Covid-19 can be treated with “nutrition, vitamins and hydroxychloroquine“.

British members of the group include Dr Mohammad Adil, an NHS surgeon who was suspended by the General Medical Council after claiming Covid-19 was a hoax.

Researchers took a sample of the 50 most popular posts from Alliance members, and categorised them into different narratives. They found the most popular claims were “conspiratorial in nature, implying some sort of overarching ‘master plan’ involving world governments, the media and healthcare authorities”.

The ISD also found serious shortcomings in Facebook’s factchecking programme, particularly regarding content in languages other than English.

One part of the company’s strategy for dealing with misinformation involves using third-party organisations to add context to misleading claims. However, a review of the 50 most popular mentioning the World Doctors Alliance revealed that just 13% of English-language posts containing false or misleading content carried a factcheck label.

In languages other than English, the proportion was even lower: 8% of German posts, 5% of Spanish posts and just 2% of Arabic posts.

Aoife Gallagher, a researcher at the ISD, said: “The approach to factchecking content one post at a time essentially acts as a plaster on a gushing wound. Many of the influencers in the Covid and vaccine misinformation spaces produce huge amounts of content, making it impossible for factcheckers to keep up with debunking efforts.”

The ISD called on Facebook to take stronger action on “misinformation super-spreaders”, increase resources dedicated to moderation and factchecking in languages other than English, and improve AI technology to assist with moderation.

A spokesperson for Facebook said it had removed the parent group for the World Doctors’ Alliance, World Freedom Alliance, in July, as well as removing 200m pieces of misinformation during the pandemic.

The spokesperson said: “Since the pandemic began, our goal has been to promote reliable information about Covid-19, take more aggressive action against misinformation, and encourage people to get vaccinated.”

The World Doctors Alliance did not respond to a request for comment.