If anyone hasn't read through these letters yet, I recommend reading them...
One letter (Simon McGrath) effectively trashes the conclusions of PACE trial mediation analysis, and points out that the investigators didn't actually demonstrate a mediation effect, and that their conclusions were not based on the evidence. (i.e. the conclusions were fabricated and based on wishful thinking rather than robust evidence - This is my own interpretation of McGrath's letter.)
Another letter (Robert Courtney) highlights that the deconditioning theory of CFS has effectively been debunked by the PACE authors, in the mediation analysis, and that the fear-avoidance theory was not supported by the PACE outcomes either.
Frank Twist points out that "fear avoidance in patients with post-exertional malaise is a reasonable and learned response, serving as a rational defence mechanism to avoid long-lasting relapses".
George Faulkner discusses the significance of objective measures in a non-blinded medical trial, and comments that "this latest report might merely be providing information about how response bias can change patient self-report measures."
And Sean Kirby asks that the authors "release the results for all of the outcomes as laid out in the published trial protocol, so that other researchers, and clinicians and patients, can decide for themselves" the value of the interventions.
The PACE authors acknowledge the limitations of the analysis as discussed by McGrath (i.e. that their conclusions were not supported by the evidence), and they then go on to say: "Most correspondents make criticisms of the trial as a whole [...] which might reflect the apparent campaign to bring the robust findings of the trial into question."
So they've engaged in a thorough and proper scientific discussion there! Not! Their response seems more like an ad hominem attack on the motives of the correspondents, rather than scientific discourse. They make ad hominen comments and then presume to judge the correspondents? I'm surprised that the Lancet published such a comment. Oh, wait, it's the Lancet.