Fact Check-Fact check: Ex-Pfizer scientist repeats COVID-19 vaccine misinformation in recorded speech

A former Pfizer scientist turned anti-vax proponent has made unfounded claims about the novel coronavirus in videos of a speech he gave that have been posted on social media.

Mike Yeadon, a former vice president of Pfizer, who recently featured in a Reuters Special Report (here), was filmed giving a speech making claims about asymptomatic infection, virus variants, the vaccine and its risks to pregnant women. The claims were viewed thousands of times on Facebook (here , here and here), and this check will examine those which are most damaging.


In his speech, Yeadon says his “favourite lie” is that people can transmit the virus without any symptoms, adding: “I would say it’s somewhere between rare and doesn’t happen.”

But a report from the United States’ Centers for Disease Control and Prevention (CDC) in March this year estimated that 50% of COVID-19 transmission happens before people develop symptoms, while 30% of infected people stay symptom-free (here). Another from January 2021, published in the JAMA Network medical journal, judged that 59% of COVID-19 transmission could be from asymptomatic cases (here).

Experts at Meedan’s Health Desk, a group of public health scientists working to tackle medical misinformation online, said that symptom-free people can spread COVID-19 and have about the same amount of virus as people with symptoms (here).


Yeadon also dismisses concerns in his speech about COVID-19 variants by claiming there is “zero chance” immunised people - either through the vaccine or prior infection - can be susceptible to them.

The same Meedan experts said this claim was false. While there are reasons to be optimistic that immunised individuals are protected against variants (here and here), mutations mean vaccines could be less effective.

Clinical trials showed the Pfizer/BioNTech vaccine, for instance, was 95% effective at preventing COVID-19 infections (here); however, a later study carried out in Qatar showed it may be less so – around 75% effective – when up against the South African variant. (here)

Natural antibodies developed after someone recovers from COVID-19 may be able to block new variants, Meedan’s experts said - but added that they would still remain cautious due to a concept called “escape mutation”, where variants evade immunity protection (here).


Another “major lie”, according to Yeadon, is that coronavirus shots are safe and effective. He points to the number of side effects listed in U.S. and UK monitoring systems as alleged proof; however, Reuters has already explained these reported reactions are not necessarily caused by the vaccine (here and here).

The shots have been proven to be safe and to give the best protection against COVID-19 (here), while regulators have acted with extreme caution over rare potential adverse reactions (here).


Later in the speech, Yeadon said a decision to immunise pregnant women “when we have not done reproductive toxicology” is further proof of pandemic falsities.

Yeadon has previously speculated, without evidence, that vaccines cause infertility in women, having launched a petition to Europe’s medicines regulator last year. This was spread widely on social media at the time (here).

Like nearly all clinical trials, COVID-19 vaccine studies initially excluded pregnant women, meaning there was limited evidence as to how they would be affected (here).

In December, Public Health England initially advised against pregnant individuals getting a COVID-19 vaccine while waiting for more data ( New advice was issued in April 2021 after real-world data from the U.S. showed 90,000 pregnant women had been safely vaccinated (here).


False. Infected but symptom-free people can spread the coronavirus; vaccinated people are better protected but not 100% immune; research shows COVID-19 vaccines are safe and effective for adults and pregnant women.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here .