                           PUBLISHED

UNITED STATES COURT OF APPEALS
                FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,               
                 Plaintiff-Appellant,
                 v.                             No. 02-1351
ST. LOUIS UNIVERSITY, a corporation,
                Defendant-Appellee.
                                        
           Appeal from the United States District Court
            for the District of Maryland, at Baltimore.
                 J. Frederick Motz, District Judge.
                        (CA-95-3639-JFM)

                      Argued: January 22, 2003

                       Decided: July 16, 2003

  Before NIEMEYER, LUTTIG, and TRAXLER, Circuit Judges.



Reversed and remanded by published opinion. Judge Traxler wrote
the majority opinion, in which Judge Niemeyer joined. Judge Luttig
wrote a dissenting opinion.


                            COUNSEL

ARGUED: Mary McElroy Leach, Senior Trial Counsel, UNITED
STATES DEPARTMENT OF JUSTICE, Washington, D.C., for
Appellant. Marc Simon Moller, KREINDLER & KREINDLER, New
York, New York, for Appellee. ON BRIEF: Robert D. McCallum,
Jr., Assistant Attorney General, Thomas M. DiBiagio, United States
Attorney, Jeffrey Axelrad, Director, Torts Branch, Civil Division,
2               UNITED STATES v. ST. LOUIS UNIVERSITY
UNITED STATES DEPARTMENT OF JUSTICE, Washington,
D.C.; Daniel E. Troy, Chief Counsel, Eric M. Blumberg, Deputy
Chief Counsel for Litigation, Michael N. Druckman, Associate Chief
Counsel for Biologics, U.S. FOOD & DRUG ADMINISTRATION,
Rockville, Maryland; Alex M. Azar, II, General Counsel, DEPART-
MENT OF HEALTH AND HUMAN SERVICES, Washington, D.C.,
for Appellant. Mark R. Dunn, HERZOG, CREBS & MCGHEE,
L.L.P., St. Louis, Missouri; Stanley P. Kops, Bala Cynwyd, Pennsyl-
vania; Rex Carr, CARR, KOREIN, TILLERY, KUNIN, MONTROY
& GLASS, East St. Louis, Missouri, for Appellee.



                              OPINION

TRAXLER, Circuit Judge:

   St. Louis University ("SLU") paid a $16 million Missouri state-
court judgment to the family of a boy who became paralyzed after
receiving Orimune, an oral polio vaccine. SLU sought contribution
from American Cyanamid, the parent company of the vaccine manu-
facturer, and United States government, which tested and approved
the vaccine. The district court granted summary judgment in favor of
Cyanamid and the government, concluding that SLU’s contribution
claims were barred by principles of collateral estoppel. We reversed
and remanded. See St. Louis Univ. v. United States, No. 99-2227 (4th
Cir. March 1, 2001); American Cyanamid v. St. Louis Univ., No. 99-
2224 (4th Cir. March 1, 2001). After remand, on motions and cross-
motions for summary judgment, the district court concluded that the
government, but not Cyanamid, was liable in contribution to SLU.
The government appeals the district court’s conclusion that it can be
required to contribute to the state-court judgment entered against SLU.1
We reverse and remand.

    1
   In American Cyanamid Co. v. St. Louis University, No. 02-1235, SLU
appeals the district court’s rejection of its contribution claim asserted
against Cyanamid. We address that appeal in a separate opinion.
                UNITED STATES v. ST. LOUIS UNIVERSITY                 3
                        I. BACKGROUND

                          A. The Vaccine

   There are three types of poliomyelitis; "Type I can be contracted
only from a Type I virus, Type II only from a Type II virus and Type
III only from a Type III virus." In re Sabin Oral Polio Vaccine Prods.
Liab. Litig., 743 F. Supp. 410, 412 (D. Md. 1990). In the 1950s, an
oral polio vaccine ("OPV") was developed that used a live but attenu-
ated or weakened polio virus. "Like all vaccines cultivated from live
viruses, OPV creates immunity by inducing a mild infection in the
recipient." Stuart v. American Cyanamid Co., 158 F.3d 622, 625 (2d
Cir. 1998). However, OPV also carries with it a risk that a recipient
(or someone in close contact with the recipient) will contract the dis-
ease through the vaccine.

   OPV is produced by passing wild virus of each type through an
animal host to develop a "strain" of attenuated virus. The vaccine
manufacturer uses the strain to grow a "seed" of each type of virus,
the seeds are used to produce monopools of each type of virus, and
"lots" of that virus type are derived from the monopools. Lots from
each type of virus are then combined into a single "trivalent" pool,
from which a trivalent vaccine can be produced to protect against all
three types of polio. See Berkovitz v. United States, 486 U.S. 531, 541
(1988).

   The United States government approved OPV in 1960 and in 1961
adopted regulations governing the manufacture of the vaccine. The
regulations required OPV to satisfy certain "neurovirulence" tests.

    Neurovirulence is the capacity of an infectious agent to pro-
    duce pathologic effects on the central nervous system. In
    this context, it refers to the vaccine’s ability to cause para-
    lytic poliomyelitis. The neurovirulence of a vaccine product
    is tested by injecting the product into monkeys. The product
    meets the neurovirulence criterion only if a specified num-
    ber of the animals survive and a comparative analysis dem-
    onstrates that the neurovirulence of the vaccine product does
    not exceed the neurovirulence of a reference product previ-
    ously selected by the agency.
4               UNITED STATES v. ST. LOUIS UNIVERSITY
Berkovitz, 486 U.S. at 545 n.9 (internal quotation marks omitted).
Under the original OPV regulations, a given monopool could be used
to produce vaccine only if its neurovirulence did not exceed that of
the reference vaccine and the monopool was one of five consecutively
made monopools that all satisfied the monkey neurovirulence test.

   The government substantially amended the monkey neurovirulence
regulations in 1991, in part because studies did not show a correlation
between higher neurovirulence scores in monkeys and the incidence
of vaccine-associated polio in humans. See Additional Standards for
Viral Vaccines, 56 Fed. Reg. 21418, 21420 (May 8, 1991) ("No single
vaccine lot has been associated with an increased incidence of polio-
myelitis. The lots that have been identified as associated with a case
of paralytic poliomyelitis have had typically low scores when tested
by FDA and the manufacturer for neurovirulence in monkeys."). In
1996, the FDA repealed a number of regulations, including the oral
polio vaccine regulations. See Revocation of Certain Regulations, 61
Fed. Reg. 40153, 40155 (August 1, 1996).

                     B. The State Court Action

   The state-court judgment paid by SLU arose from SLU’s actions
in treating 3-month old Danny Callahan. Approximately one month
after receiving a dose of Orimune, Danny developed a fever and a
perirectal abscess. He was treated at Cardinal Glennon Hospital by
hospital and SLU employees. Although the abscess improved,
Danny’s legs and left arm were permanently paralyzed. Type III polio
virus was isolated in Danny’s stool, and doctors ultimately concluded
that Danny suffered from vaccine-associated polio.

   The plaintiffs’ theory of the case was that SLU improperly treated
Danny’s abscess by giving him the wrong kind of antibiotic. The
improper treatment allowed the release of endotoxins, which sup-
pressed Danny’s immune system during a time when the polio virus
from the vaccine was still replicating in Danny’s gastrointestinal tract.
Because Danny’s immune system was compromised, the attenuated
polio virus in the vaccine was able to replicate fast enough to over-
come his suppressed immune system, resulting in poliomyelitis. The
plaintiffs’ experts testified that if the abscess had immediately been
incised and drained as required by the standard of care, and if Danny
                UNITED STATES v. ST. LOUIS UNIVERSITY                  5
had been treated with an appropriate antibiotic, the endotoxins would
not have been released and his immune system would not have been
suppressed. Thus, the expert witnesses testified that if Danny had
been treated properly, he would not have been paralyzed by the polio
vaccine. The jury’s $16 million verdict in favor of the plaintiffs was
affirmed by the Missouri Supreme Court. See Callahan v. Cardinal
Glennon Hosp., 863 S.W.2d 852 (1993) (en banc).

                           C. In re Sabin

   While Callahan v. Cardinal Glennon Hospital was proceeding
through the Missouri state courts, multi-district Orimune cases filed
against the United States government under the Federal Tort Claims
Act were transferred to the District of Maryland for resolution of the
common legal and factual questions. See In re Sabin Oral Polio Vac-
cine Prods. Liab. Litig., 743 F. Supp. 410 (D. Md. 1990); In re Sabin
Oral Polio Vaccine Prods. Liab. Litig., 763 F. Supp. 811 (D. Md.
1991); In re Sabin Oral Polio Vaccine Prods. Liab. Litig., 774 F.
Supp. 952 (D. Md. 1991) ("Sabin III").2 The Sabin plaintiffs con-
tracted polio after receiving the Orimune vaccine or after coming into
contact with a recipient of the vaccine. They sued the government,
alleging, inter alia, that the government negligently approved for
release the vaccine lots which contained the doses given to the plain-
tiffs, even though the vaccine seeds from which the lots were derived
did not meet the neurovirulence standards set forth in the governing
regulations.

   The district court ultimately concluded that the government could
be held liable for approving vaccine lots that did not comply with the
regulatory requirements for neurovirulence. Applying the "Good
Samaritan" principles of the Restatement (Second) of Torts, the dis-
trict court determined that the government, by violating its own regu-
latory standards and approving for release vaccine derived from seeds
that exceeded the neurovirulence standards, had increased the risk of
harm for those receiving the vaccine, which proximately caused the
plaintiffs’ injuries. Sabin III, 774 F. Supp. at 958. This court affirmed
the district court’s causation and liability determination. See In re
  2
   The district judge presiding over the cases currently before us also
presided over the In re Sabin cases.
6               UNITED STATES v. ST. LOUIS UNIVERSITY
Sabin Oral Polio Vaccine Prods. Liab. Litig., 984 F.2d 124 (4th Cir.
1993) (per curiam) ("Sabin IV"). The Orimune vaccine received by
Danny Callahan was derived from one of the vaccine seeds that the
district court in the Sabin cases concluded were improperly approved
by the government.

               II. THE CONTRIBUTION ACTION

   After the Missouri Supreme Court affirmed the Callahan verdict,
SLU filed a contribution action in Maryland against the United States,
alleging that Danny Callahan’s polio was caused by the governmental
failings identified in the Sabin cases. The government moved for par-
tial summary judgment, arguing that SLU was barred by collateral
estoppel from relitigating the Callahan jury’s conclusion that SLU’s
malpractice caused Danny’s polio. The district court agreed, conclud-
ing that SLU was prohibited from relitigating the facts that the court
believed the Callahan jury necessarily found in order to reach its ver-
dict against SLU: (1) that SLU breached the applicable standard of
care when treating Danny’s abscess; (2) that Danny’s immune system
would not have been suppressed but for SLU’s inadequate treatment
of the abscess; (3) that, but for the suppressed state of Danny’s
immune system, the live polio virus contained in the vaccine would
not have been able to replicate fast enough to cause polio; and (4)
that, but for SLU’s negligence, Danny would not be paralyzed. The
district court’s collateral estoppel order prevented SLU from arguing
that it was not negligent at all or that any negligence on its part did
not contribute to Danny’s polio, but the ruling allowed SLU to pro-
ceed on any theory consistent with the Callahan verdict. Thus, after
the collateral estoppel order, SLU could still prevail if it could estab-
lish that an immunosuppressed child would not have contracted polio
from a vaccine that complied with all regulatory requirements.

   After the collateral estoppel ruling, the parties engaged in eighteen
months of discovery. The government then moved for summary judg-
ment on the ground that SLU could not prove that the government’s
negligence caused Danny’s polio. The district court reviewed the evi-
dence submitted by SLU and concluded that it was insufficient, given
the Callahan findings, to establish a causal connection between the
government’s negligence and Danny’s injuries. The district court
                UNITED STATES v. ST. LOUIS UNIVERSITY                   7
therefore granted summary judgment to the government on SLU’s
contribution claim.

   We reversed and remanded, concluding that the district court
improperly applied Missouri law when it held that the Callahan jury
verdict had collateral estoppel effect on SLU’s contribution action
against the government. We explained that Missouri law did not limit
SLU to causation theories predicated on the Callahan jury’s implicit
conclusion that Danny would not have contracted polio but for SLU’s
negligence which resulted in the suppression of his immune system.
However, the district court had limited SLU during discovery to cau-
sation theories consistent with its ruling as to the collateral estoppel
effect of the Callahan judgment, and the district court premised its
order granting summary judgment on SLU’s failure to present evi-
dence of causation consistent with its collateral estoppel ruling.
Because of the district court’s error with regard to the collateral estop-
pel issue, we reversed the district court’s grant of summary judgment
to allow SLU an opportunity to develop other appropriate theories of
causation.

   After remand, SLU offered no new evidence, deposed no new wit-
nesses, and offered no new theory of causation. Instead, it relied
almost exclusively on the fact that in the Sabin cases, the court deter-
mined that the government’s regulatory violations caused the injuries
at issue. SLU argued that Danny Callahan’s polio vaccine came from
one of the seeds that the district court in Sabin had concluded the gov-
ernment negligently approved in violation of its own regulatory stan-
dards. Since the Sabin court had concluded that the government’s
failings proximately caused the injuries of the Sabin plaintiffs, SLU
suggested that those same regulatory violations must also be held to
have proximately caused Danny’s injuries.

   The district court agreed with SLU. Applying the same analysis the
court had used in Sabin III, the district court concluded that the gov-
ernment’s negligence in approving vaccine that did not satisfy the
neurovirulence standards caused Danny’s polio. The district court
therefore granted partial summary judgment to SLU, concluding that
the government was liable in contribution to SLU, but reserving for
8               UNITED STATES v. ST. LOUIS UNIVERSITY
later the determination of the extent of the government’s liability to
SLU.3

                           III. ANALYSIS

   The government’s liability in contribution, of course, is dependent
on SLU’s ability to establish that the government can be held liable
on the tort claim in the underlying action. See United States v. Yellow
Cab Co., 340 U.S. 543, 546-50 (1951) (concluding that the waiver of
sovereign immunity under the Federal Tort Claims Act encompasses
claims for contribution if the law of the relevant state would hold a
private individual liable for contribution in the same circumstances);
Gramex Corp. v. Green Supply, Inc., 89 S.W.3d 432, 442 (Mo. 2002)
(en banc) ("To maintain an action for contribution, both the party
seeking contribution and the defendant against whom contribution is
sought must be tortfeasors, originally liable to the plaintiff-injured
party." (alterations and internal quotation marks omitted)). The gov-
ernment contends that SLU presented no evidence showing that the
government’s violations of the original polio vaccine regulations
proximately caused the injuries suffered by Danny Callahan. Accord-
ing to the government, the district court’s approach to the case
amounts to the imposition of absolute liability for the government,
which is inconsistent with the requirements of the Federal Tort
Claims Act and does not meet the causation requirements of Missouri
law. Given the absence of any admissible proximate cause evidence,
the government contends that the district court must have reached its
decision by giving collateral estoppel effect to its decision in Sabin
III, but that collateral estoppel cannot be applied against the govern-
ment in this case.

                                   A.

    We first consider the government’s arguments as to whether the
decisions in the Sabin cases must be given controlling effect in this
litigation. At the outset, we can dispense with the government’s claim
that the district court improperly gave collateral estoppel effect to the
    3
   The district court certified the order as appropriate for immediate
review, and this court granted the government permission to bring this
interlocutory appeal. See 28 U.S.C.A. § 1292(b) (West 1993).
                UNITED STATES v. ST. LOUIS UNIVERSITY                  9
Sabin decisions, an action which might well have been error. See
United States v. Mendoza, 464 U.S. 154, 162 (1984) (rejecting the use
of offensive nonmutual collateral estoppel against the government).
The district court expressly did not give the Sabin cases collateral
estoppel effect. Instead, it appears that the court viewed the cases as
establishing binding precedent on the question of proximate cause.
See St. Louis Univ. v. United States, 182 F. Supp. 2d 494, 500 n.5 (D.
Md. 2002) ("I am not relying upon the doctrine of collateral estoppel,
which may not be invocable against the government. I am simply fol-
lowing my reasoning in Sabin III that was affirmed on appeal." (cita-
tion omitted)). The question, then, is whether Sabin III and our
decision in Sabin IV serve as binding precedent in this case. We think
the answer to that question is no.

   Under the Federal Tort Claims Act, state law, not federal law,
serves as "the source of substantive liability." FDIC v. Meyer, 510
U.S. 471, 478 (1994). The Act requires the government’s liability to
be determined "in accordance with the law of the place where the act
or omission occurred." 28 U.S.C.A. § 1346(b)(1) (West Supp. 2003).
The Supreme Court has concluded that the "law of the place" refers
to the "whole law," including choice-of-law principles of the state
where the negligent act or omission occurred. See Richards v. United
States, 369 U.S. 1, 11 (1962).

   Because the government’s actions with regard to the polio vaccine
took place in Maryland, see Sabin III, 774 F. Supp. at 953-54, Mary-
land law, including its choice-of-law principles, governs this case, just
as it governed the Sabin cases. Under Maryland’s choice-of-law prin-
ciples, the law to be applied in tort cases is the law of the state where
the injury was suffered, not where the negligent act occurred. See
Johnson v. Oroweat Foods, Inc., 785 F.2d 503, 511 (4th Cir. 1986).
Danny Callahan was injured in Missouri, so Missouri law applies to
SLU’s claim against the government. But the plaintiffs in the Sabin
cases were residents of Maryland and Florida and suffered their inju-
ries in those states. Thus, 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. Accordingly, notwithstanding the factual overlap of the
10               UNITED STATES v. ST. LOUIS UNIVERSITY
cases, the analyses of Sabin III and Sabin IV simply do not govern
this case.4

                                   B.

   Under Missouri law, a plaintiff seeking to hold a defendant liable
in tort must establish the existence of a duty on the part of the defen-
dant to protect the plaintiff, a breach of that duty, and damages caused
by the breach. See, e.g., L.A.C. ex rel. D.C. v. Ward Parkway Shop-
ping Ctr. Co., 75 S.W.3d 247, 257 (Mo. 2002) (en banc). In this case
(and the Sabin cases), the district court concluded that the govern-
ment’s duty arose under the "Good Samaritan" doctrine, through
which liability may be imposed for the negligent execution of volun-
tarily undertaken duties. See Hoover’s Dairy, Inc. v. Mid-America
Dairymen, 700 S.W.2d 426, 432-33 (Mo. 1985) (en banc) (following
Good Samaritan standards set forth in Restatement (Second) of Torts
§§ 323, 324A (1965)). For purposes of this litigation, the government
has agreed to be bound by the findings in the Sabin cases that it
breached its duty by violating the OPV regulations. See St. Louis
Univ., 182 F. Supp. 2d at 498. Thus, the only issue before the district
court was whether SLU could establish that Danny Callahan’s injuries
were caused by the government’s breach of duty.

   The district court concluded that SLU had sufficiently established
that the government’s regulatory violations caused Callahan’s inju-
ries. The court explained that in Sabin III,

      I held that proximate cause was established by the mere fact
      that if seeds 45 B 85 and 45 B 165 had not been in use, the
      vaccine giving rise to the injuries would not have been man-
      ufactured. The evidence clearly establishes that but for the
      United States’s negligence, the seeds would not have been
      used. I went on to reject an ancillary contention made by the
  4
   Even assuming that SLU is correct in its contention that the tort laws
of Maryland and Missouri are similar, it makes little sense for this court
to apply Missouri law by way of Sabin III and Sabin IV, cases that
applied Maryland and Florida law. Instead, we will go directly to the
source and consult Missouri cases to determine whether SLU has satis-
fied the requirements of Missouri law.
                 UNITED STATES v. ST. LOUIS UNIVERSITY                 11
      government that proximate cause was dispelled by the fact
      that the specific lots involved in the two cases under consid-
      eration had met the regulatory neurovirulence criteria, and
      I concluded that the causal connection between the regula-
      tory violations and plaintiffs’ injuries are logical, sensible
      and direct. The Fourth Circuit affirmed this holding on
      appeal.

         My reasoning in Sabin III is equally applicable here. This
      can be most easily seen by hypothesizing that SLU is correct
      in contending that the immunosuppression allegedly caused
      by its malpractice played absolutely no role in making Cal-
      lahan susceptible to contracting polio from OPV. If that is
      true, Callahan stands in exactly the same position as did the
      plaintiffs in other Sabin cases because in that event the sole
      cause of his polio was the vaccine. Likewise, even if the
      immunosuppression did play some role in the disease pro-
      cess, Callahan’s exposure to the oral vaccine had to be a
      contributing cause to his paralysis. The isolation of Type III
      polio virus in Callahan’s stool demonstrates he contracted
      polio, and no one suggests that the immunosuppression
      alone could have caused the disease. Accordingly, as I held
      in Sabin III, Callahan was exposed to the virus as a conse-
      quence of the government’s violation of the OPV regula-
      tions. If the government had not wrongfully approved the
      seed from which the vaccine was derived, Callahan would
      never have been administered a dose of Orimune and would
      never have contracted polio even if he had been immuno-
      suppressed. This "but for" relationship meets the standard of
      proximate cause under Missouri law just as it does under the
      law of Maryland and Florida applicable in Sabin III.

St. Louis Univ., 182 F. Supp. 2d at 499-500 (footnotes, alterations,
and internal quotation marks omitted)).

 We assume, of course, that Sabin III and Sabin IV properly applied
Maryland and Florida law.5 Nonetheless, it is clear that the approach
  5
   The government points out that when this court in Sabin IV affirmed
the proximate cause analysis in Sabin III, we relied on Waffen v. United
12              UNITED STATES v. ST. LOUIS UNIVERSITY
taken in the Sabin cases is inconsistent with the requirements of Mis-
souri law, which governs this case. Under Missouri law, a plaintiff
must establish both causation-in-fact and proximate cause. See
Callahan, 863 S.W.2d at 862, 865; Robinson v. Missouri State High-
way & Transp. Comm’n, 24 S.W.3d 67, 77 (Mo. Ct. App. 2000) (per
curiam).

        A defendant’s conduct is the cause in fact of a plaintiff’s
     injuries where the injuries would not have occurred but for
     that conduct. Proximate cause is not causation in fact, but is
     a limitation the law imposes upon the right to recover for the
     consequences of a negligent act. The requirement of proving
     proximate cause absolves those actors whom it would be
     unfair to punish because of the attenuated relation which
     their conduct bears to the plaintiff’s injury.

Robinson, 24 S.W.3d at 77 (citations and internal quotation marks
omitted). The district court’s conclusion that Danny Callahan would
not have contracted polio "but for" the government’s action thus goes
only to the question of causation-in-fact, not proximate cause,
because it does not answer the question of whether the particular
result that occurred was a reasonable and probable consequence of the
government’s conduct. See Callahan, 863 S.W.2d at 865 (Missouri
courts "have generally said that the injury must be a reasonable and
probable consequence of the act or omission of the defendant.").

   The district court’s explanation of why different results were
required as to the claims against the government and Cyanamid, the

States Department of Health & Human Services, 799 F.2d 911 (4th Cir.
1986), which considered causation requirements under Maryland law in
the context of a claim for loss of chance of survival. Subsequent cases
from this court and Maryland state courts have indicated that Waffen did
not accurately articulate the contours of Maryland’s proximate cause
requirements. See Hurley v. United States, 923 F.2d 1091, 1096 (4th Cir.
1991) ("Our interpretation of Maryland law in Waffen is called into ques-
tion because we were interpreting Maryland law as espoused in Hetrick
v. Weimer, which was later reversed by the Maryland Court of Appeals."
(footnote omitted)); Cooper v. Hartman, 533 A.2d 1294, 1297 & n.4
(Md. 1987) (placing Waffen among a group of decisions that improperly
"relaxed the standards regarding causation").
                UNITED STATES v. ST. LOUIS UNIVERSITY                13
vaccine manufacturer, suggests that the court believed the causation
standard is different in cases where the duty arises under the Good
Samaritan doctrine. The court stated:

    I find that Cyanamid cannot be held liable for contribution
    to SLU and that it is therefore entitled to summary judg-
    ment. While I recognize that this holding may seem asym-
    metrical, paradoxical, or even perverse in light of my
    finding that the government is liable for contribution, the
    difference in result flows from the difference in the nature
    of the respective duties owed by the United States and Cya-
    namid to those who were exposed to the live virus contained
    in OPV.

       As indicated above, in Sabin III I ruled that the Good
    Samaritan doctrine and its parallel provision, Restatement
    (Second) of Torts § 323, imposed upon the government the
    duty not to approve vaccine seeds in violation of the OPV
    regulations. Cyanamid was under no such duty. Its duties
    and responsibilities to the members of the public, particu-
    larly to OPV recipients and their families, [are] defined by
    products liability law. In considering claims against Cya-
    namid, the focus must therefore be on the safety of its prod-
    uct, not the regulatory process for which the government
    bore responsibility. Likewise, in analyzing the element of
    proximate cause in claims against Cyanamid, the focus must
    be on whether the plaintiff can prove that it was a defect in
    the OPV that resulted in his injury, not simply—as in a case
    against the government—whether he had been exposed to
    OPV derived from a seed that had been improperly
    approved in violation of the regulatory process. Under Mis-
    souri law this element of causation is required whether a
    plaintiff sues for strict liability, negligence, or breach of
    warranty.

St. Louis Univ., 182 F. Supp. 2d at 500. Missouri law, however,
makes it quite clear that the Good Samaritan doctrine is relevant to
the question of duty only; it has no effect on the general rules of cau-
sation. See Wollen v. DePaul Health Center, 828 S.W.2d 681, 683
(Mo. 1992) (en banc) ("[T]his Court has recognized that section 323
14              UNITED STATES v. ST. LOUIS UNIVERSITY
[of the Restatement (Second) of Torts] creates a duty of care. In creat-
ing this duty, this section of the Restatement defines a type of negli-
gent behavior but does not alter the rules of causation." (citation
omitted)). Thus, SLU’s claim against the government requires evi-
dence of proximate cause in addition to evidence of but-for causation.

   As to proximate cause, we note that all OPV, including OPV that
satisfied all regulatory requirements, carried the risk that the recipient
would actually contract polio. Therefore, to show that Danny’s polio
was caused by the government’s regulatory violations, we conclude
that SLU was required to establish that Danny likely would not have
contacted polio (or would have contracted a less severe case of polio)
from a vaccine that satisfied the government’s neurovirulence require-
ments. Any lesser standard would result in the government being held
strictly liable for its regulatory violations, which would be inconsis-
tent with Missouri law. See Sill v. Burlington No. R.R., 87 S.W.3d
386, 392 (Mo. Ct. App. 2002) (explaining that the violation of a stat-
ute can, under certain circumstances, support a negligence per se
claim, but that the plaintiff must prove that the statutory "violation
was the proximate cause of the injury."). And this evidence, of course,
must be in the form of expert testimony. See, e.g., Wright v. Barr, 62
S.W.3d 509, 524 (Mo. Ct. App. 2001) ("If there is a sophisticated
injury, one that requires surgical intervention or other highly scientific
techniques for diagnosis, expert medical testimony is required to
prove causation.").

   There is no such evidence in this record. At best, SLU’s experts
assumed that increased neurovirulence led to increased incidence of
vaccine-associated polio, but SLU’s experts did not offer that opinion.
In fact, none of SLU’s experts were even qualified to render such an
opinion.6 The district court recognized this absence of evidence, see
St. Louis Univ., 182 F. Supp. 2d at 502 ("Whether or not an oral polio
  6
   In the first appeal, this court noted that there was some evidence that
a more neurovirulent vaccine caused Danny to have a more severe case
of polio. SLU, however, did not pursue this theory after remand and does
not pursue it on appeal. Moreover, the district court concluded that the
expert who provided this testimony was not qualified to render an opin-
ion on causation, and SLU does not challenge that determination on
appeal.
                UNITED STATES v. ST. LOUIS UNIVERSITY                15
vaccine that complied with the OPV regulations would have caused
Callahan and the plaintiffs in the other Sabin cases to contract polio
ultimately is unknowable and unprovable."), as does SLU. SLU, how-
ever, insists that it is not required to present evidence of proximate
cause.

   According to SLU, the regulations establishing the neurovirulence
standards created an "unrebuttable presumption" that any vaccine
exceeding the standards posed an unacceptable risk that the recipient
would contract polio. Brief of Appellee at 21. Thus, SLU contends
that once it was established in the Sabin cases that the government
violated its regulations and that the violations proximately caused the
injuries, the government was automatically liable for the injuries suf-
fered by anyone who received a vaccine derived from one of the vac-
cine seeds at issue in the Sabin cases. As noted above, such an
approach is utterly inconsistent with Missouri law. See Sill, 87
S.W.3d at 392 ("If a submissible case is made under a negligence per
se cause of action, a plaintiff could recover if a jury concluded that
a statute was violated and the violation was the proximate cause of
the injury."); Friend v. Yokohama Tire Corp., 904 S.W.2d 575, 579
(Mo. Ct. App. 1995) ("One of the elements of a negligence per se
action is that the violation of a statute was the proximate cause of the
injury.").

   Because there is no evidence that the government’s regulatory vio-
lations proximately caused Danny’s injury, SLU has failed to show
that it is entitled to contribution from the government. We therefore
reverse the district court’s grant of partial summary judgment in favor
of SLU and we remand for the entry of judgment in favor of the gov-
ernment. See Monahan v. County of Chesterfield, Va., 95 F.3d 1263,
1265 (4th Cir. 1996) (explaining that where cross-motions for sum-
mary judgment have been filed, the appellate court can direct the
entry of judgment in favor of the appellant).

                                      REVERSED AND REMANDED

LUTTIG, Circuit Judge, 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
16               UNITED STATES v. ST. LOUIS UNIVERSITY
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 9, 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 9. This 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 hold-
ings. 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 (i.e., functionally identical underlying tort regime,
facts, and causation theories). In this manner, Sabin IV binds us as a
matter of federal law, delimiting the open field that we would other-
wise 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 the-
ories, that were functionally indistinguishable from those before us
today. But, absent such a denial, it has no basis on which to reach the
                UNITED STATES v. ST. LOUIS UNIVERSITY                 17
conclusion it reaches today other than that it disagrees with the rea-
soning we adopted in Sabin IV. While I am somewhat sympathetic to
the critique the majority implicitly levels at that reasoning, the major-
ity, 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 IV, the majority
asserts that the district court erred here because it engaged in no prox-
imate cause determination whatsoever. But Sabin IV 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 deter-
    mination that [the government’s] approval of the lots was
    the proximate cause of [the plaintiff’s] injuries. The test of
    probable [sic] cause is one of "reasonable probability or rea-
    sonable certainty." In other words, "the plaintiff has the bur-
    den 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)(1)(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). Like-
         wise, regardless of the acceptability of the lots
         from which the vaccine administered to [the plain-
         tiff] 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.
18              UNITED STATES v. ST. LOUIS UNIVERSITY
        The government’s argument that the failure to amend the
     regulation was not the proximate cause of the plaintiff’s
     injuries misconstrues the plaintiff’s 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 rea-
soning — 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 govern-
ment being held strictly liable for its regulatory violations, which
would be inconsistent with Missouri law." Ante at 14. As an initial
matter, strict liability effects culpability standards (e.g., negligence,
recklessness, etc.), not causation standards. That every regulatory vio-
lation 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 Calla-
han’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 rea-
soning 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 dif-
                UNITED STATES v. ST. LOUIS UNIVERSITY                  19
ferently 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 par-
ticular 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 distri-
bution. 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 causa-
tion of injury by one’s "defective" action is quite different from the
other, since one’s "defect-free" action keeps all product from the mar-
ket while the other instead distributes defect-free product. Since Flor-
ida 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 govern-
ment’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 per-
suasive, for us to conclude in Sabin IV that the alleged conduct proxi-
mately 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 artic-
ulates this aspect of the case. That the majority instead thinks this
notation signals that the lower court mistakenly "believed the causa-
tion standard is different in cases where the duty arises under the
Good Samaritan doctrine[,]" ante at 13 (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
20                UNITED STATES v. ST. LOUIS UNIVERSITY
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 mat-
ter 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 dis-
sent’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.
