18 Mar 2021 – Late last year, a semi-retired British scientist co-authored a petition to Europe’s medicines regulator. The petitioners made a bold demand: Halt COVID-19 vaccine clinical trials.

Even bolder was their argument for doing so: They speculated, without providing evidence, that the vaccines could cause infertility in women.

The document appeared on a German website on Dec.1. Scientists denounced the theory. Regulators weren’t swayed, either: Weeks later, the European Medicines Agency approved the European Union’s first COVID-19 shot, co-developed by Pfizer Inc. But damage was already done.

Social media quickly spread exaggerated claims that COVID-19 jabs cause female infertility. Within weeks, doctors and nurses in Britain began reporting that concerned women were asking them whether it was true, according to the Royal College of Obstetricians & Gynaecologists. In January, a survey by the Kaiser Family Foundation (KFF), a non-profit organization, found that 13% of unvaccinated people in the United States had heard that “COVID-19 vaccines have been shown to cause infertility.”

What gave the debunked claim credibility was that one of the petition’s co-authors, Michael Yeadon, wasn’t just any scientist. The 60-year-old is a former vice president of Pfizer, where he spent 16 years as an allergy and respiratory researcher. He later co-founded a biotech firm that the Swiss drugmaker Novartis purchased for at least $325 million.

“These claims are false, dangerous and deeply irresponsible.”

In recent months, Yeadon (pronounced Yee-don) has emerged as an unlikely hero of the so-called anti-vaxxers, whose adherents question the safety of many vaccines, including for the coronavirus. The anti-vaxxer movement has amplified Yeadon’s skeptical views about COVID-19 vaccines and tests, government-mandated lockdowns and the arc of the pandemic. Yeadon has said he personally doesn’t oppose the use of all vaccines. But many health experts and government officials worry that opinions like his fuel vaccine hesitancy – a reluctance or refusal to be vaccinated – that could prolong the pandemic. COVID-19 has already killed more than 2.6 million people worldwide.

“These claims are false, dangerous and deeply irresponsible,” said a spokesman for Britain’s Department of Health & Social Care, when asked about Yeadon’s views. “COVID-19 vaccines are the best way to protect people from coronavirus and will save thousands of lives.”

Recent reports of blood clots and abnormal bleeding in a small number of recipients of AstraZeneca’s COVID-19 vaccine have cast doubt on that shot’s safety, leading several European countries to suspend its use. The developments are likely to fuel vaccine hesitancy further, although there is no evidence of a causative link between the AstraZeneca product and the affected patients’ conditions.

Yeadon didn’t respond to requests for comment for this article. In reporting this story, Reuters reviewed thousands of his tweets over the past two years, along with other writings and statements. It also interviewed five people who know him, including four of his former colleagues at Pfizer.

A Pfizer spokesman declined to comment on Yeadon and his stint with the company, beyond emphasizing that there is no evidence that its vaccine, which it developed with its German partner BioNTech, causes infertility in women.

References to Yeadon’s petition appear on the website of a group founded by influential vaccine skeptic Robert F. Kennedy Jr., scion of the American political dynasty, who recently was banned on Instagram because of his COVID-19 vaccine posts. Syndicated writer and vaccine skeptic Michelle Malkin reported Yeadon’s concern about fertility in a column last month under the headline, “Pregnant Women: Beware of COVID Shots.” And a blog with an alarmist headline – “Head of Pfizer Research: Covid vaccine is female sterilization” – was shared thousands of times on Facebook.

The visage and views of Yeadon, widely identified as an “Ex-VP of Pfizer,’’ can be seen on social media in languages including German, Portuguese, Danish and Czech. A Facebook post carries a video from November in which Yeadon claimed that the pandemic “fundamentally… is over.” The post has been viewed more than a million times.

In October, Yeadon wrote a column for the United Kingdom’s Daily Mail newspaper that also appeared on MailOnline, one of the world’s most-visited news websites. It declared that deaths caused by COVID-19, which then totaled about 45,000 in Britain, will soon “fizzle out” and Britons “should immediately be allowed to resume normal life.” Since then, the disease has killed about another 80,000 people in the UK.

Yeadon isn’t the only respected scientist to have challenged the scientific consensus on COVID-19 and expressed controversial views.

Michael Levitt, a winner of the Nobel Prize for chemistry, told the Stanford Daily last summer that he expected the pandemic would end in the United States in 2020 and kill no more than 175,000 Americans – a third of the current total – and “when we come to look back, we’re going to say that wasn’t such a terrible disease.” And Luc Montagnier, another Nobel Prize winner, said last year that he believed the coronavirus was created in a Chinese lab. Many experts doubt that, but so far there is no way to prove or disprove it.

Levitt told Reuters that his projections about the pandemic in the United States were wrong, but he still believes COVID-19 eventually won’t be seen as “a terrible disease” and that lockdowns “caused a great deal of collateral damage and may not have been needed.” Montagnier didn’t respond to a request for comment.

What gives Yeadon particular credibility is the fact that he worked at Pfizer, says Imran Ahmed, chief executive of the Center for Countering Digital Hate, an organization that combats online misinformation. “Yeadon’s background gives his dangerous and harmful messages false credibility.”

In a debate last fall in Britain’s House of Commons about the government’s response to the pandemic, parliamentarian Richard Drax called Yeadon an “eminent” scientist, and cited his view “that the virus is both manageable and nearing its end.” Drax didn’t respond to a request for comment.

More recently, David Kurten, a member of the London Assembly – an elected body – tweeted there is a “real danger” that COVID-19 vaccines could leave women infertile. “The ‘cure’ must not be worse than the ‘disease’,” Kurten wrote. He, too, didn’t respond to a request for comment.

Why Yeadon transformed from mainstream scientist to COVID-19 vaccine skeptic remains a mystery. Thousands of his tweets stretching back to the start of the pandemic document a dramatic shift in his views – early on, he supported a vaccine strategy. But they offer few clues to explain his radical turnabout.

Some former colleagues at Pfizer say they no longer recognize the Mike Yeadon they once knew. They described him as a knowledgeable and intelligent man who always insisted on seeing evidence and generally avoided publicity.

One of those ex-colleagues is Sterghios A. Moschos, who holds degrees in molecular biology and pharmaceutics. In December, Yeadon posted on Twitter a spoof sign that said, “DITCH THE MASK.” Moschos tweeted back: “Mike what hell ?! Are you out to actively kill people? You do realize that if you are wrong, your suggestions will result in deaths ??”

“It’ll all fade away”

Yeadon joined Twitter in October 2018 and soon became a prolific user of the platform. The thousands of his tweets reviewed by Reuters were provided by archive.org, which stores web pages, and FollowersAnalysis, a social media analytics company.

When the coronavirus pandemic reached the UK in March 2020, Yeadon initially expressed support for developing a vaccine. He tweeted: “Covid 19 is not going away. Until we have a vaccine or herd immunity” – natural resistance resulting from prior exposure to the virus – “all that can be done is to slow its spread.” A week later he tweeted: “A vaccine might be along towards the end of 2021, if we’re really lucky.”

When a fellow Twitter user said vaccines “harm many, many people,” Yeadon replied: “Ok, please refuse it, but do not impede its flow to neutrals or those keen to get it, thanks.”

After Mathai Mammen, the global head of research & development for Janssen, the pharmaceutical division of Johnson & Johnson, posted on LinkedIn last summer that his company had started clinical trials of a vaccine, Yeadon responded: “Lovely to see this milestone, Mathai!” Mammen didn’t respond to a request for comment.

But as early as April, Yeadon had begun voicing unorthodox views.

While Britain was still in its first lockdown last spring, he declared: “there is nothing especially virulent or frightening about covid 19 … it’ll all fade away … Just a common & garden virus, to which the world overreacted.” And he predicted in a subsequent tweet that it was “unlikely” the death toll in the UK would reach 40,000.

By September 2020, Yeadon’s statements were attracting attention beyond Twitter. At the time, a movement had emerged in Britain against lockdowns and other restrictions meant to curb the disease. He co-authored a lengthy article on a website called Lockdown Sceptics. It declared that the “pandemic as an event in the UK is essentially complete.” And, “There is no biological principle that leads us to expect a second wave.” Britain soon entered a much more deadly second wave.

On Oct. 16, he wrote another lengthy article for the same website: “There is absolutely no need for vaccines to extinguish the pandemic. I’ve never heard such nonsense talked about vaccines. You do not vaccinate people who aren’t at risk from a disease.”

In November, Yeadon appeared in a 32-minute video for the anti-lockdown group, Unlocked, sitting in a shed with a motorbike behind him. A shorter version appeared on Facebook titled, “The pandemic is over.”

Yeadon called for an end to mass testing and claimed that 30% of the population was already immune to COVID-19 even before the pandemic started. By the time of the recording, he said, there was little scope for the virus to spread further in the UK because most people had already been infected or were immune.

Those views ran counter to the findings of the World Health Organization. In December – nine months after declaring the COVID-19 outbreak a pandemic – the agency said testing suggested that less than 10% of the world’s population had shown evidence of infection.

Yeadon’s petition to the European Medicines Agency to halt vaccine trials followed on Dec. 1. The agency didn’t respond to requests for comment for this article.

“This does not sound like the guy I knew 20 years ago.”

It’s impossible to measure the impact of Yeadon’s claim that COVID-19 vaccines could cause female infertility. Anecdotally, though, many women have bought into it.

Bonnie Jacobson, a waitress in Brooklyn, New York, can’t recall where she first heard about the fertility issue. But she told Reuters that it has made her hesitant to take a vaccine, as she’d like to have children “sooner than later.”

“That’s my main concern,” she said. “Let more research come out.” After recently declining to get vaccinated, she said, the tavern where she worked fired her. Jacobson’s employer didn’t respond to a request for comment.

A good scientist

According to Yeadon’s LinkedIn profile, he joined Pfizer in 1995;  the company had a large operation then in Sandwich in southern England. He rose to become a vice president and head of allergy and respiratory research.

Many former colleagues say they are baffled by his transformation.

Mark Treherne, chairman of Talisman Therapeutics in Cambridge, England, said he overlapped with Yeadon at Pfizer for about two years and sometimes had coffee with him. “He always seemed knowledgeable, intelligible, a good scientist. We were both trained as pharmacologists … so we had something in common.”

“I obviously disagree with Mike and his recent views,” he said. Treherne’s company is researching brain inflammation, which he said could be triggered by coronaviruses. “This does not sound like the guy I knew 20 years ago.”

Moschos, the ex-colleague who took issue with one of Yeadon’s tweets, said he considered him a mentor when they worked together at the drugmaker from 2008 to 2011. More recently, Moschos has been researching whether it’s possible to test for COVID-19 with breath samples. He said Yeadon’s views are “a huge disappointment.” He recounted hearing Yeadon in a radio interview last year.

“There was a tone in his voice that was nothing like I ever remembered of Mike,” Moschos said. “It was very angry, very bitter.”

John LaMattina, a former president of Pfizer Global Research and Development, also knew Yeadon. “His group was very successful and discovered a number of compounds that entered early clinical development,” LaMattina told Reuters in an email. He said Yeadon and his team were let go by Pfizer, however, when the company made the strategic decision to exit the therapeutic area they were researching.

LaMattina said he had lost touch with Yeadon in recent years. Shown links to Yeadon’s video declaring the pandemic over and a copy of his petition to halt COVID-19 clinical trials, LaMattina replied: “This is all news to me and a bit of a shock. This seems out of character for the person I knew.”

“Chutzpah”

After losing his job at Pfizer in 2011, Yeadon set up a biotech company called Ziarco with three Pfizer colleagues. They wanted to continue researching promising therapies that targeted allergies and inflammatory diseases, ideas Pfizer had been developing but were at risk of being abandoned. Yeadon served as Ziarco’s chief executive.

“I simply showed chutzpah and asked the senior-most people up the research line” at Pfizer to support the venture, Yeadon later recalled in an interview with Forbes. “And they said, ‘OK, assuming you raise private capital.’”

In 2012, Ziarco announced it had initially secured funding from several investors, including Pfizer’s venture capital arm. Other investors later joined, including an Amgen Inc corporate venture capital fund. Amgen didn’t respond to a request for comment.

“The intensity of effort took me away almost completely from my family and other interests for almost five years and you get only one life,” Yeadon told Forbes.

On Twitter, Yeadon said he is married and has two adult daughters, and described a tough childhood – he said his mother committed suicide when he was 18 months old and his father, a doctor, abandoned him when he was 16. He said he was saved by a local social worker and adopted by a Jewish family whose “open handed love turned my life around.”

While at Ziarco, Yeadon also worked as a consultant for several years at two Boston-area biotech companies, Apellis Pharmaceuticals and Pulmatrix Inc. Both firms said he no longer advises them. A spokeswoman for Apellis said, “His views do not reflect those of Apellis.” She didn’t elaborate.

The hard work at Ziarco paid off. In January 2017, Novartis acquired the company for an upfront payment of $325 million, with the promise of $95 million more if certain milestones were met, according to Novartis’ 2017 annual report. Novartis was betting on the promise of a Ziarco drug, known as ZPL389, that had the potential to be a “first-in-class oral treatment for moderate-to-severe eczema,” a common and sometimes debilitating rash.

Reuters wasn’t able to determine how much money Yeadon made from Novartis’ purchase of Ziarco. But in January 2020 he tweeted: “Oddly enough, I made millions from founding & growing a biotech company, creating many highly paid jobs, using my PhD & persuasion around the world.”

Last July, Novartis disclosed it had discontinued the ZPL389 clinical development program and had taken a $485 million write down. A Novartis spokesman said the company decided to terminate the program after disappointing efficacy data in an early-stage clinical trial.

“I’ll soon be gone”

Earlier this year, a group of Yeadon’s former Pfizer colleagues expressed their concern in a private letter, according to a draft reviewed by Reuters.

“We have become acutely aware of your views on COVID-19 over the last few months … the single mindedness, lack of scientific rigour and one sided interpretation of often poor quality data is far removed from the Mike Yeadon we so respected and enjoyed working with.”

Noting his “vast following on social media” and that his claim about infertility “has spread globally,” the group wrote, “We are very worried that you are putting people’s health at risk.”

Reuters couldn’t determine whether Yeadon received the letter.

On Feb. 3, Yeadon’s Twitter account had a message for his 91,000 followers: “A tweet recently appeared under my ID, which was horribly offensive. As a result my account was locked. I of course deleted it. I want you to know of course that I didn’t write it.” A Twitter spokesman declined to comment.

Yeadon didn’t make clear what tweet he was referring to. But shortly after, several Twitter users and a blog called Zelo Street posted screenshots of numerous offensive anti-Muslim tweets from Yeadon’s account from about a year ago. Many were captured at the time by archive.org.

The next day, on Feb. 4, Yeadon cryptically mentioned in a tweet, “I’ll soon be gone.”

Two days later, he was off Twitter. His followers were greeted with this message: “This account doesn’t exist.” His LinkedIn profile also soon changed, now stating that he is “Fully retired.”

Clare Craig, a British pathologist, compared Yeadon’s treatment on Twitter – where some users derided his views as nonsense and dangerous – to medieval societies burning heretics at the stake.

“There is no other way to see it than the burning of the witches,” said Craig, who has criticized lockdowns and COVID-19 tests. “Science is always a series of questions and the testing of those questions and when we are not allowed to ask those questions, then science is lost.”

She said she spoke to Yeadon after he closed his Twitter account. “He will have a think about how he will contribute in the future,” she said.