dissenting:
I would affirm the district court’s judgment in this case under the binding precedent of the circuit. In In re Sabin Oral Polio Vaccine Products Liability Litigation, 984 F.2d 124 (4th Cir.1993) (“Sabin IV”), we determined that under a tort regime, identical in all relevant respects to the one at issue here, an injury, identical to the one at issue here, was proximately caused by tortious conduct identical to that alleged here. On the basis of the reasoning which we adopted in that case, I must conclude that our application here of Missouri state law yields the conclusion that appellee SLU proffered sufficient evidence to establish the legally necessary causation for it to prevail.
The majority reaches the opposite conclusion. It reasons that “our decision in Sabin IV [does not] serve as binding precedent in this case,” ante at 300, because “the proximate cause determination in Sabin III was reached by applying Maryland and Florida law, while the proximate cause determination in this case must be made by applying Missouri law.” Ante at 300. *305This reasoning would be compelling if SLU proposed that we apply the state law holdings of Sabin IV to the facts of the case before us today. But, the majority is wrong to suggest that SLU, or by implication, I, argue that Sabin IV is binding as a matter of Missouri state law. All that SLU asks, and all that I contend is appropriate, is that we reach our judgment by applying the binding reasoning of Sabin IV.
While our decision in Sabin IV resulted in state law holdings, it also produced reasoning, by which we reached those state law holdings. This reasoning is uniquely the creature of this court, and, as it is binding upon us, we must apply it in other cases involving the same predicate facts (ie., functionally identical underlying tort regime, facts, and causation theories). In this manner, Sabin TV binds us as a matter of federal law, delimiting the open field that we would otherwise face in formulating our reasoning. Because the question before us is simply how we will reason to our application of Missouri’s tort regime, which regime is functionally identical in the relevant regards to those from which we reasoned in Sabin IV, our conclusion as to how to reason to this application is governed by Sabin IV.
The majority, to its credit, does not attempt to deny the crucial point in this case, namely, that in Sabin IV we reasoned from two state tort law regimes, from injuries, and from asserted causation theories, that were functionally indistinguishable from those before us today. But, absent such a denial, it has no basis on which to reach the conclusion it reaches today other than that it disagrees with the reasoning we adopted in Sabin TV. While I am somewhat sympathetic to the critique the majority implicitly levels at that reasoning, the majority, as am I, is bound to abide by it until this court en banc or the Supreme Court holds otherwise.
Having mistakenly rejected the authority of Sabin TV, the majority asserts that the district court erred here because it engaged in no proximate cause determination whatsoever. But Sabin TV quite clearly shows the majority to be in error on this point. There, we concluded that an identical causation theory, in the unique circumstance where the tortfeasor’s function is that of a product-approver, suffices to establish proximate cause. We reasoned as follows:
The final point of appeal concerns the district court’s determination that [the government’s] approval of the lots was the proximate cause of [the plaintiffs] injuries. The test of probable [sic] cause is one of “reasonable probability or reasonable certainty.” In other words, “the plaintiff has the burden of introducing evidence which affords a reasonable basis for the conclusion that it is more likely than not that the conduct of the defendant was a substantial factor in bringing about the result.”
The district court concluded:
Regardless of the acceptability of the specific lots from which were derived the vaccine ... if [the government] had properly applied 42 C.F.R. § 73.114(b)(l)(iii) ... the seed would not have been used. This is so because the manufacturer would have been unable to satisfy the consistency requirement found in 42 C.F.R § 73.116(c). Likewise, regardless of the acceptability of the lots from which the vaccine administered to [the plaintiff] were derived, the lots would never have been produced and released but for the approval of [the] seed.... Thus, the causal connections between the regulatory violations and plaintiffs’ injuries are logical, sensible and direct.
*306The government’s argument that the failure to amend the regulation was not the 'proximate cause of the plaintiffs injuries misconstrues the plaintiffs claims and the district court’s opinion. [The government’s] liability arose out of releasing vaccine in violation of the regulations, not in its failure to amend the regulations.
Sabin IV, 984 F.2d at 128 (emphasis added) (citations omitted).
By this passage, we clearly concluded that the district court’s reasoning — what the majority here terms a merely but-for causation analysis — constituted a proper proximate cause analysis with respect to a tortfeasor who functions as a unilateral product-approver. Under this binding precedent, we are required to conclude that the district court’s identical reasoning here is likewise a proper proximate cause analysis.
The majority’s underlying dissatisfaction with this analysis seems based on the belief that such an analysis “would result in the government being held strictly liable for its regulatory violations, which would be inconsistent with Missouri law.” Ante at 803. As an initial matter, strict liability effects culpability standards (e.g., negligence, recklessness, etc.), not causation standards. That every regulatory violation in the circumstance where the government is a product-approver is the proximate cause of injuries sustained by the use of the defectively approved product simply does not create strict liability since under Missouri law it still must be proven that the violation was the result of negligence or recklessness.
And, while I am somewhat sympathetic to the majority’s other apparent concern— that the government is treated differently than the manufacturer with regards to the causal effect of its action in Callahan’s injury — we may not base our judgment on it, for it is quite clear that we have already concluded that the district court’s analysis, distinguishing between the two parties’ causal effects, was proper. And this determination binds us, regardless of whether our prior reasoning as to why it is so is persuasive.
The majority’s concern on this score, however, is not even fully borne out. That the causal effect of the government’s conduct is differently understood than that of the manufacturer is the result of the fact that the government’s role as tortfeasor here springs from its actions as a product-approver. As opposed to a manufacturer, who presumably sells a range of product, some with and some without defect, a product-approver’s only role is to determine whether a particular product goes to market at all. In this unique role, failure, and breach of a duty of care, does not result in any easy comparison between what would have happened had the defective “product” not been defective, because, for such a tortfeasor, the defective “product” is the failure to withhold completely the distributed item from distribution. Thus, had the government’s “product” been free of defect, none of the offending vaccine would have been distributed at all. This contrasts with the case of a manufacturer who, had its product been defect free, would have distributed a defect free product. The causation of injury by one’s “defective” action is quite different from the other, since one’s “defect-free” action keeps all product from the market while the other instead distributes defect-free product. Since Florida and Maryland law, just like Missouri law, require plaintiffs to prove proximate cause by demonstrating that, had the product been defect-free, the injury would not have occurred, and since the government’s defect-free product would have been the complete withholding of the vaccine, it was not too great of a stretch, even if not wholly persuasive, for *307us to conclude in Sabin IV that the alleged conduct proximately caused the alleged injury-
The district court’s notation that its causation analysis took into account that the government acted under a Good Samaritan duty articulates this aspect of the case. That the majority instead thinks this notation signals that the lower court mistakenly “believed the causation standard is different in cases where the duty arises under the Good Samaritan doctrine[,]” ante at 302 (emphasis added), illustrates the panel’s failure to appreciate how a manufacturer’s defect causes injury in one way, while defective product approval causes injury in another. That different causal relationships exist between different categories of conduct and the injury they cause bespeaks nothing as to what legal standard applies to those causal relationships in a tort action.
But even if there were any merit to the majority’s concerns that our prior analysis effectively creates a strict liability culpability standard or a but-for causation standard and treats the government differently from the manufacturer, those issues have already been fought over and decided— and not by today’s opinion. Sabin IV decided the matter and so provides binding reasoning, which, if we were to apply it today, would result in affirmance of the district court’s judgment. Indeed, the rule we face not only binds us, but also every district court within our circuit and every future panel of our court, and the dissent’s judgment only evades that reality temporarily. See Booth v. Maryland, 327 F.3d 377, 382-83 (4th Cir.2003) (explaining that it is error to follow the more recent of two contradicting panels).
For these reasons, I respectfully dissent.