We had the pleasure of speaking on a panel at ACI last week, including discussion of the terrific order from the Zantac MDL excluding all the plaintiffs’ general causation experts.  That order essentially did away with an entire MDL and came in fourth on our list of best decisions of 2022 .  Our thoroughly enjoyable panel discussion of that Rule 702 order caused us to go back through the files to see if there were other good expert orders that we may have missed.  That review turned up an order from the Zostavax MDL that is eminently blogworthy.

The order is In re Zostavax Products Liability Litig., No. 18-md-2848, 2023 WL 6626581 (E.D. Pa. Oct. 11, 2023), and technically we did not “miss” it.  Bexis does not miss anything, and Lisa Baird posted a one-paragraph update on this decision back when it came out.  There are, however, a few interesting angles we thought we could amplify. 

The Zostavax MDL has been mainly about shingles, but as we reminded you all just the other day, the shingles cases essentially went kaput because the plaintiffs could not prove causation.  The leftovers have fared no better, with the district court dismissing a case alleging peripheral neuropathy and excluding expert causation opinions on persistent daily headaches. 

The plaintiff in the order we are covering today alleged that he came down with Guillian-Barré syndrome, a rare autoimmune disorder characterized by diffuse weakness, just days after he received a Zostavax vaccine.  But as we reported in our update, the district court excluded the plaintiff’s expert on specific causation because his differential diagnosis did not pass muster.  There are four points we wanted to highlight. 

First, the district court dealt with general causation first and concluded that the plaintiffs’ experts’ reliance on epidemiological studies (or more accurately, one epidemiological study) was sound methodology.  The defendants obviously disagreed, and the court freely acknowledged that there was scientific evidence going the other way.  But at least the court ruled on general causation before it engaged in a differential diagnosis.  We have seen courts skip that step altogether, leaving us to wonder how a defendant’s product can be “ruled in” as a potential cause when it has not yet been established that the product is capable of causing the alleged injury in the first place.  This court did not make that mistake. 

Second, the court credited the experts’ reliance on epidemiology, but threw serious shade on one expert’s reliance on case reports and adverse event reports, which are “‘universally recognized as insufficient and unreliable evidence of causation’ in the absence of other reliable evidence.”  Id. at *5.  In other words, case reports are anecdotal and are make-weight evidence at best.  Thus, while experts can justifiably rely “in part” on them, “reliance on case reports should be minimized because they do not take into account the background rate of disease.”  Id.

Third, the court ruled that temporal proximity alone was insufficient to “rule in” the defendant’s vaccine as a potential cause.  This is a significant ruling because, in many cases, the only basis for the plaintiff’s case is that he or she experienced symptoms at some time after exposure to the defendant’s product.  Here, the plaintiff’s specific causation expert “ruled in” the vaccine based on the short time (three days) between when the plaintiff received the vaccine and when his symptoms began.  But that could have been a coincidence, and even the plaintiff’s expert conceded that contracting Guillian-Barré syndrome “less than one week after a triggering infection is unusual.”  Id. at *6.  The court ruled that the expert’s “ruling in” of Zostavax failed because of his “after this, therefore because of this” reasoning.  Id.

Fourth, the court ruled that the plaintiff’s expert’s differential diagnosis was unreliable and inadmissible also because he had not ruled out idiopathic causes.  This is a significant ruling too, because many diseases and conditions occur for unknown or unexplained causes (see, for example, mesothelioma).  This expert admitted that approximately one-third of Guillian-Barré syndrome cases resulted from unknown or unexplained causes, and his own clinical experience was that one-half of the cases he had seen were idiopathic.  Id. at *6.  Yet, the expert did not rule out idiopathic causes in his differential diagnosis, which doomed his opinions.  We do not take this ruling necessarily to mean that an expert has to rule out idiopathic causes in every case.  When, however, a significant number of cases are idiopathic, it needs to be on the differential.

So take these useful nuggets and run with them.  From a broader view, we will echo what we have said before—that this MDL seems to be on its last legs, with a hodgepodge of allege injuries and judge who is proactively steering the leftovers to a dignified conclusion.  We will keep you posted.