On 2020-08-28 07:43:07, user Hilda Bastian wrote:
At several points, the authors rely on what's described as the "historical efficacy of passive antibody therapy for infectious diseases". This is based on a small amount of data, much of it from the pre-intensive care era, and none from a publication later than 2010. As a result, no randomized trial is included, as they were published after 2010: 2 NIH randomized trials of convalescent plasma in influenza and 2 randomized trials of IVIG for influenza. Meta-analysis shows no benefit. [1] This also fails to consider the post-2010 ebola outbreak, and the failure of convalescent plasma to improve mortality from that disease. [1] Thus, there is no historically proof of efficacy of convalescent plasma, and what randomized data exists, does not suggest there has been important benefit in the past.
In addition to relying on this biased assessment of historical evidence to support a conclusion of effectiveness in this study, the authors cite this claim as a reason for not conducting a randomized trial: "Many COVID-19 patients would likely have been distrustful of being randomized to a placebo based on historical precedent". However, if they were accurately informed, prospective participants would be told there was no evidence of benefit. In a randomized trial in the Netherlands stopped because it was determined no benefit was likely in the study as designed, the authors reported that only 1 in 4 eligible patients declined, and that was typically because of fear of adverse events. [2] The requirement for adequate trial recruitment has more to do with doctors and patients in outbreaks not being misled about the state of uncertainty of this treatment.
The authors argue that the patients in the Expanded Access Program are diverse. However, it is important to point out that their diversity is not representative of the people severely ill with Covid-19 and at risk of dying. For example, 19% of the group are Black, whereas the CDC reports that they are over 30% of those hospitalized with Covid-19 and twice as likely to die. [3,4]
In respect of the representativeness of the small non-random sample described as "pseudo-randomized" in this preprint, no data is provided on the hospitals providing those samples.
In addition, as others have already pointed out in a discussion linked here, [5] critical information on timing of deaths is not provided. Those transfused earlier in the "epochs" have far longer follow-up for deaths than the larger number more recently. Given that since early in the outbreak, it's been observed that deaths occur across 2 to 8 weeks from the onset of symptoms, [6] the impact of this could be substantial, as participation in the EAP was higher later. In the group on the Diamond Princess cruise, for example, per Wikipedia's tallying, half the deaths may have occurred in that second month [7], and assessment of mortality appropriately included censoring for this. [8] Case series in the US typically report substantial proportions of people still in intensive care at study's end.
The authors' interpretation of their subgroup analysis based on a non-random set of blood samples preserved for blood bank quality assurance proceeds as though the safety of convalescent plasma for Covid-19 has been established, based on the data of their own uncontrolled study. However, controlled study is required to be certain, for example, whether plasma with lower levels of antibodies trigger antibody dependent disease enhancement. [5] As the FDA's memorandum reports that the results are also dependent on which assay results are used, this should be reported in any discussion of this subgroup analysis. [9]
In the absence of adequate controlled study of convalescent plasma establishing that it does more good than harm in infectious respiratory disease generally in contemporary medical settings, and Covid-19 in particular, the authors' claim that their uncontrolled study provides "strong evidence" is unjustified.
Disclosure: I have written about this study for the general public at WIRED, and am in the process of doing so at PLOS Blogs.
[1] Devasenapathy (2020). https://www.cmaj.ca/content...
[2] Gharbharan (2020). https://www.medrxiv.org/con...
[3] CDC COVID-Net (2020). https://gis.cdc.gov/grasp/C...
[4] CDC surveillance data (2020). https://www.cdc.gov/coronav...
[5] Harrell (2020). https://discourse.datametho...
[6] WHO (2020). https://www.who.int/docs/de...
[7] Wikipedia (2020). https://en.wikipedia.org/wi...
[8] Russell (2020). https://www.medrxiv.org/con...
[9] FDA Clinical Memorandum (2020). https://www.fda.gov/media/1...