[13] In 2008, the media psychiatrist Raj Persaud was suspended from practicing medicine and resigned his academic position after being found guilty of plagiarism following an investigation by Deer.

[14][15] In a series of reports[16] between 2004[17] and 2010,[18] for The Sunday Times, Deer investigated and helped debunk controversial claims linking the MMR vaccine to autism that had first emerged with the publication in 1998 of a fraudulent research paper in the medical journal The Lancet written by Andrew Wakefield, and his colleagues.

[19] Deer revealed that Wakefield had multiple undeclared conflicts of interest,[20][21] had manipulated evidence,[22] and was responsible for what the BMJ later called "an elaborate fraud".

[27][28] In January 2011, Deer published his findings in the BMJ[29][30][31] which in a signed editorial stated of the journalist, "It has taken the diligent scepticism of one man, standing outside medicine and science, to show that the paper was in fact an elaborate fraud.

[33][34] Television critic Nancy Banks-Smith wrote in The Guardian: "After a year of rebuffs, Deer ran Dr Wakefield to ground at an Indianapolis conference on autism.

[37][38] In October 2014, in an article published in The Sunday Times, Deer reported on a ruling from the Court of Protection, then recently made public but with the identities of the parties redacted.

[40] In September 2020 Johns Hopkins University Press published in North America Deer's investigation of Andrew Wakefield and the origins of the anti-vaccine movement in his book, The Doctor Who Fooled the World: Science, Deception, and the War on Vaccines.

"[41] Reviewing for the leading science journal Nature, Saad Omer praised the book as "riveting… a compelling portrait of hubris and the terrible dark shadow it can cast.

"[42] Among other reviews, Michael Shermer in The Wall Street Journal wrote, "Exposing researchers who lie, cheat and fake their data often requires the work of courageous whistleblowers or tenacious investigative journalists.