Recently, when we have spoken of vaccine litigation, it has mostly been about challenges to public health policies requiring vaccination against COVID-19 for healthcare workers, students at public universities, etc.  We have been pleased to report that these challenges have been failing without lingering too long at the trial court level, like here, here, and here.  There was a time when lawsuits against the manufacturers of a number of different vaccines were prevalent and fiercely litigated.  One of the responses to this was the enactment of the National Childhood Vaccine Injury Act of 1986, which set up a fund for compensation for certain injuries allegedly connected to certain vaccines and preempted tort claims against manufacturers of those same vaccines.  The Supreme Court upheld the Act’s preemption provision in 2011 and, since then, product liability litigation over vaccines has been relatively quiet.  The Act does not cover the vaccine for herpes zoster (shingles) and, things being as they are in litigation, there is a fairly large (about 2500 pending cases) MDL about whether the shingles vaccine causes shingles.

The MDL is in the Eastern District of Pennsylvania before Judge Bartle.  (While we do not go as far back as some, we recall hearings before Judge Bartle from long ago, including on a case where the novel claim that was eventually recognized on appeal in Lance was first offered up.)  We have blogged about a number of good rulings from this MDL, ranging from personal jurisdiction  to pleadings to statutes of limitations to legal malpractice.  The litigation has progressed to bellwether cases and a challenge to plaintiffs’ specific-causation expert.  In re Zostavax (Zoster Vaccine Live) Prods. Liab. Litig., MDL No. 2848, 2021 WL 5631687 (E.D. Pa. Dec. 1, 2021).  To spoil the suspense, the court excluded the challenged causation opinions as to five plaintiffs in a well-reasoned opinion that saw through the sort of misdirection that sometimes trips up courts when applying Rule 702 to specific-causation opinions.

The bane of our existence when it comes to Rule 702 and specific-causation is some courts’ misapprehension of the concept of differential diagnosis.  (See here and here for some flavor of our discontent.)  In addition to the general concern about courts shirking their gatekeeping responsibility, we have seen cases where a reference to an expert’s use of a differential diagnosis (or differential etiology) with a plaintiff was seen as satisfying the quite separate requirement of general causation.  We have seen cases where the claim that the defendant’s product was the most likely cause of the potential causes considered was enough; to be the likely cause, it would have to be more likely than all the other potential causes put together.  We have seen cases where the analysis into whether a potential cause was properly ruled out was no deeper than “the expert says she did so using her training, experience, and clinical judgment.”  We have seen cases where diagnostic studies, pathology, or images were interpreted by the plaintiff’s expert well beyond how they were interpreted by the plaintiff’s treating physicians.  We have seen cases where a call to a temporal relationship weighed heavily in favor of the reliability of the challenged causation opinion even without examining why the timing of the exposure to the defendant’s product and the onset of the alleged complications was supposedly supportive.

The decision in Zostavax makes none of these mistakes.  What it does in excluding the challenged expert’s specific-causation opinions as unreliable is display the value of common sense in carrying out the gatekeeping role.  Rather than explaining the court’s analysis as to each plaintiff separately—as the court did—we will lump them together.  The first issue the court recognized was the logical difficulty of sorting out specific causation when the allegation was that a vaccine caused the condition that it was supposed to prevent, given that the vaccine did not have (or promise) 100% efficacy and the condition occurs anyway in the relevant population.  Because shingles occurs from reactivation of the virus that causes chicken pox and almost everyone over 30 in the U.S. has had chicken pox, approximately 1/3 of adults develop shingles during their lifetimes.  Id. at *1.  The reactivation apparently happens randomly or can be brought on by a variety of stressors.  Thus, the court’s statement that “There is no doubt that defendants have presented an obvious alternative cause of the plaintiffs’ shingles, that is, the activation of the natural wild-type virus latent in their bodies” could apply to any plaintiff who did not have the simple PCR test to distinguish between the type of virus used in the vaccine and the one that caused their past chicken pox.  Id. at *3.  “A simple PCR test?” one might ask.  “Then why, pray tell, don’t we just look at the test results for each plaintiff?”  Well, these five did not have them.  Why not?  We do not know.

The implication should be obvious, though.  For a differential diagnosis to be meaningful—and the Third Circuit was an early adopter of looking to a differential diagnosis as a potentially reliable methodology for a specific causation opinion (paired with a reliable general causation opinion)—there needs to much more than a guess that the shingles was from the virus in the vaccine as opposed to the lurking dormant virus’s reactivation.  Perhaps the rash caused by the shingles—its typical manifestation—looks different depending on which virus caused it, something the expert seemed to imply for at least one of the plaintiffs.  That cannot be a reliable basis where the expert has not even seen a picture of the rash and cannot identify medical literature describing different appearances by the type of virus (but the manufacturer can identify literature saying they do not look different).  Id. at 4.  Maybe the temporal relationship of vaccination to onset of symptoms provides a reliable basis.  But the times to onset in these five plaintiffs were seven days, ten days, four months, one year, and four years, all of which the expert claimed supported causation even though he had no basis in the literature.

The court cannot admit expert testimony based solely on the post hoc ergo propter hoc fallacy, that is, the fallacy that the mere happening of an evidence such as vaccination injection must be the cause of a later happening such as an illness of injury.

Id. at *7 (citations omitted).  We wish more courts could see that inconsistent approaches to causation by the same expert undercut the reliability of his opinions as to all, because the inconsistency tends to show the expert uses no methodology other than justifying a foregone conclusion.

Other arguments for ruling out the “wild” virus in favor the virus in the vaccine were considered.  Maybe the location of the rashes or their duration suggested some sort of fingerprint for the vaccine.  Nope.  There was no literature supporting that and the plaintiffs had very different presentations.  What about the absence of some potentially triggering stress before the rash occurred?  Again, some had identifiable stresses and some did not.  For those who did, the expert pivoted to the idea that maybe the vaccine’s virus had been triggered.  “[S]ince stress can activate shingles whether or not a person has received the vaccine, any reliance on stress as causing shingles from the live-attenuated virus as opposed to the wild-type virus cannot stand.”  Id. at *6.

At the end of the day, there was just no basis for ruling out the “wild” virus for any of these plaintiffs and it was apparent that it was the expert’s ipse dixit at the root of his opinion, his call to a differential diagnosis notwithstanding.  We cannot say it better than the court did:

During the lengthy oral argument on the pending motion, the court asked plaintiffs’ counsel to guide the court to the place or places in the expert reports or the deposition of Dr. Poznansky where he ruled out the reactivation of wild-type virus as the cause of shingles suffered by the plaintiffs. Counsel, with appreciated candor, conceded that there is nothing to this effect as to any plaintiff in Dr. Poznansky’s initial and third reports and nothing explicit in his second report. Likewise, counsel could not cite anything on point in Dr. Poznansky’s deposition. At best, according to counsel, any ruling out of the wild-type virus is implicit or must be inferred. Unfortunately for plaintiffs, no straining or stretching of the words of Dr. Poznansky can satisfy Daubert or Rule 702 of the Federal Rules of Evidence.

Id. at *9.  The Zostavax court’s insistence that the expert explain how he reached his conclusion in each step of his purported differential diagnosis is something we would like to see from more courts in fulfilling their gatekeeping role.  Sometimes, differential diagnosis is just going to be a label, not a true methodology for evaluating specific causation.