[2] He has been criticised for suggesting COVID-19 deaths have been over-counted,[3] repeating false claims about the use of ivermectin as a COVID-19 treatment, and providing misleading commentary about the safety of COVID-19 vaccines.

A review in Emergency Nurse magazine said that the latter textbook contained "excellent [and] inexpensive notes on the causes, pathophysiological changes, and clinical features seen in disease processes".

Referencing a study on mice, he said that myocarditis could be caused if the person injecting the vaccine does not perform aspiration (checking that the needle does not hit a blood vessel by initially drawing back the plunger).

However, the drug had never been officially authorised for such use in the country; its use was merely promoted by the chair of a non-governmental medical association in Tokyo and it has no established benefit as a COVID-19 treatment.

"[2] In November 2021, Campbell quoted from a non-peer-reviewed standalone journal abstract by Steven Gundry saying that mRNA vaccines might increase the risk of heart attack, and said that this might be "incredibly significant".

[24] This video was viewed over 2 million times within a few weeks and was used by anti-vaccination activists as support for the misinformation that COVID-19 vaccination causes heart attacks.

[24] According to a FactCheck.org review, although Campbell had drawn attention to the abstract's typos and its lack of methodology and data, he did not mention the expression of concern that had been issued against it.

[25] In October 2022, Campbell uploaded a YouTube video in which he said he was sharing a scandalous "revelation" that the Pfizer COVID-19 vaccine did not prevent viral transmission, something he claimed had been hitherto hidden from the public.

[20] In December 2022 Campbell posted a video in which he made selective use of statistics to make the misleading claim that COVID-19 vaccines were so harmful that they should be withdrawn.

David Spiegelhalter, chair of Cambridge University's Winton Centre for Risk and Evidence Communication, said that such use of the data seemed "entirely inappropriate".

[26] In February 2023, nanomedicine specialist Susan Oliver published a YouTube video debunking false information Campbell has posted about vaccine brain injury.

[3] In January 2022, Campbell posted a video in which he cited figures from the British Office for National Statistics (ONS) and suggested that they showed deaths from COVID-19 were "much lower than mainstream media seems to have been intimating".

[3][33] In October 2023, the BBC Radio 4 programme More or Less debunked a video that Campbell had made in September 2023 in which he wrongly claimed that excess deaths were higher among those who had had a COVID-19 vaccine than those who had not; the figures he used in fact showed the opposite.

The misinformation was embraced and amplified by Jimmy Dore and his comedy co-host Kurt Metzger, achieving wide currency on social media.