Court Opinion

ID: 4695561
Source: CourtListenerOpinion
Date Created: 2021-06-15 15:03:00.379917+00
Date Added: 2024-06-11T08:05:36.032014
License: Public Domain

Case: 20-2282   Document: 40     Page: 1   Filed: 06/15/2021

        NOTE: This disposition is nonprecedential.

   United States Court of Appeals
       for the Federal Circuit
                 ______________________

     MARYELLEN KOTTENSTETTE, NICHOLAS
   KOTTENSTETTE, AS BEST FRIENDS OF THEIR
             DAUGHTER (C.K.),
             Petitioners-Appellants,

                            v.

 SECRETARY OF HEALTH AND HUMAN SERVICES
             Respondent-Appellee.
            ______________________

                       2020-2282
                 ______________________

    Appeal from the United States Court of Federal Claims
 in Case No. 1:15-vv-01016-RAH, Judge Richard A.
 Hertling.
                 ______________________

                 Decided: June 15, 2021
                 ______________________

    JOHN F. MCHUGH, Law Office of John McHugh, New
 York, NY, argued for petitioners-appellants.

    CAMILLE M. COLLETT, Torts Branch, Civil Division,
 United States Department of Justice, Washington, DC, ar-
 gued for respondent-appellee. Also represented by BRIAN
 M. BOYNTON, C. SALVATORE D’ALESSIO, HEATHER L.
 PEARLMAN.
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 2                                       KOTTENSTETTE v. HHS

                   ______________________

     Before O’MALLEY, REYNA, and STOLL, Circuit Judges.
 O’MALLEY, Circuit Judge.
      Maryellen and Nicholas Kottenstette (“the Kotten-
 stettes”), on behalf of their daughter, appeal the final judg-
 ment of the United States Court of Federal Claims and a
 prior non-final decision by that court in the same case.
 Kottenstette v. Sec’y of HHS (Kottenstette II), No. 15-1016V,
 2020 WL 4592590 (Fed. Cl. July 27, 2020); Kottenstette v.
 Sec’y of HHS (Kottenstette I), No. 15-1016V, 2020 WL
 953484 (Fed. Cl. Feb. 12, 2020). Two special masters made
 determinations in this case. Kottenstette v. Sec’y of HHS
 (Special Master Decision II), No. 15-1016V, 2020 WL
 4197301 (Fed. Cl. June 2, 2020), aff’d, Kottenstette II, 2020
 WL 4592590; Kottenstette v. Sec’y of HHS (Special Master
 Decision I), No. 15-1016V, 2017 WL 6601878 (Fed. Cl. Dec.
 12, 2017), vacated, Kottenstette I, 2020 WL 953484. The
 first special master found for the Kottenstettes. Special
 Master Decision I, 2017 WL 6601878. The Court of Federal
 Claims vacated and remanded her decision, finding that
 she had applied an incorrect legal standard to one aspect
 of her analysis. By the time the case had been remanded,
 she had retired, so the case was assigned to a second spe-
 cial master. The second special master reweighed the evi-
 dence and determined that the Kottenstettes had not
 provided preponderant evidence that vaccines were a cause
 of their daughter’s injury. Special Master Decision II, 2020
 WL 4197301. The Court of Federal Claims affirmed that
 decision. Kottenstette II, 2020 WL 4592590. We reverse
 both Court of Federal Claims decisions.
                        BACKGROUND
    The Kottenstettes’ daughter, C.K., was born on June 1,
 2012. Until October 2, 2012, she appeared to be a happy
 and healthy, normally developing child. On the morning of
 October 2, 2012, she had her four-month pediatrician
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  KOTTENSTETTE   v. HHS                                      3

 appointment, during which she received four vaccines:
 pneumococcal conjugate (“PCV”); inactivated poliovirus
 (“IPV”); haemophilus influenzae type b (“Hib”); and diph-
 theria, tetanus, and acellular pertussis (“DTaP”). During
 her appointment, she appeared “alert, vigorous, in no acute
 distress, well developed and well nourished.” J.A. 124.
 Less than ten hours later, C.K. experienced the first of life-
 long infantile spasms. During her initial infantile spasms,
 C.K. appeared alert and, other than unusual arm move-
 ments, did not appear to be unwell. Over time, however,
 C.K. has suffered vision impairment and major develop-
 mental delays due to her infantile spasms.
     On September 11, 2015, C.K.’s parents, Maryellen and
 Nicholas Kottenstette, filed a petition on her behalf for
 compensation under the National Childhood Vaccine In-
 jury Act of 1986 (“Vaccine Act”), 42 U.S.C. §§ 300aa-1 to
 300aa-34. They alleged that C.K. suffers infantile spasms
 accompanied by a chronic encephalopathy and that vac-
 cination was a cause of her condition. 1
      In support of their petition, the Kottenstettes filed an
 expert report and a supplemental expert report by Dr. Mar-
 cel Kinsbourne, a pediatric neurologist. The government
 filed an expert report by Dr. John Zempel, a pediatric neu-
 rologist and pediatric epileptologist.
     Dr. Kinsbourne presented a “two hit model of seizure
 susceptibility” in which an infant has a pre-existing condi-
 tion that makes them more susceptible to infantile spasms
 (the first hit) and undergoes an adverse or stressful event

     1   “Encephalopathy is a term for any diffuse disease
 of the brain that alters brain function or structure.” NAT’L
 INST. OF NEUROLOGICAL DISORDERS & STROKE, Encephalo-
 pathy Information Page, https://www.ninds.nih.gov/Disor-
 ders/All-Disorders/Encephalopathy-Information-Page (last
 visited May 10, 2021).
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 4                                      KOTTENSTETTE v. HHS

 (the second hit) which triggers seizures which can lead to
 worsening psychomotor regression if not immediately con-
 trolled. J.A. 916. He opined that, in C.K.’s case, the first
 hit was the hyperexcitability of her infantile neural net-
 work, which may be caused by prenatal stress. He rea-
 soned that C.K.’s four-month vaccines were likely the
 “second hit” as they “necessarily evoked an innate immune
 system reaction, which in turn generated proinflammatory
 cytokines.” J.A. 916. Dr. Kinsbourne cited several studies
 to support his theory. He cited two of those studies as sup-
 port for the proposition that vaccinations such as DTP and
 DTaP can trigger the onset of infantile spasms: the Bell-
 man and Melchior studies.
      The Bellman study found an increase in cases of infan-
 tile spasms in the week following DTP immunization as
 compared to controls, and fewer cases of infantile spasms
 in the second week after DTP vaccination. The authors of
 the Bellman study surmised that the pertussis part of the
 DTP vaccine “may precipitate the onset of spasms in those
 children in whom the disorder is already destined to de-
 velop,” causing spasms to develop sooner than they other-
 wise would have. J.A. 911; J.A. 1234. It is undisputed that
 earlier onsetting uncontrolled infantile spasms generally
 cause greater long-term impact than spasms which occur
 later in infancy.
      The Melchior study analyzed the effect of changing the
 date of administration of the DTP vaccine from five months
 of age to five weeks of age in Denmark. The children who
 received the earlier (five week) vaccination experienced the
 onset of infantile spasms before two months of age twice as
 often as the children who received the later (five month)
 vaccination. The author of the Melchior study concluded
 “that a causal connection between [pertussis] immuniza-
 tion and infantile spasms is very unlikely except in a few
 cases and that time-coincidence is the most likely fac-
 tor. . . .” Special Master Decision I, 2017 WL 6601878, at
 *4.
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  KOTTENSTETTE   v. HHS                                    5

      The government’s expert, Dr. Zempel, 2 disagreed with
 Dr. Kinsbourne’s application of the two-hit model. He re-
 jected Dr. Kinsbourne’s opinion that vaccinations could be
 the “second hit” because Dr. Kinsbourne cited no medical
 literature or objective independent evidence from treating
 physicians for this proposition. He also objected to Dr.
 Kinsbourne’s characterization of the Bellman and Melchior
 studies. He criticized the studies for discussing DTP rather
 than DTaP, the vaccine C.K. received. He understood that
 the Bellman study concluded that pertussis vaccine might
 precipitate the onset of spasms in children who would even-
 tually develop them in any case but was not a direct cause
 of infantile spasms. And he stated that the Melchior study
 actually showed that there was “no change in the onset of
 infantile spasms” but for an occasional, coincidental “con-
 nection between immunization and infantile spasms.” Spe-
 cial Master Decision I, 2017 WL 6601878, at *6.
     On December 12, 2017, the first special master found
 that the Kottenstettes had prevailed on their allegations
 that C.K.’s October 2, 2012 vaccinations were a cause of her
 infantile spasms and resulting chronic encephalopathy.
 Special Master Decision I, 2017 WL 6601878, at *2.
     She found that both sides’ expert witnesses, Dr. Kins-
 bourne and Dr. Zempel, agreed on several points: (1) C.K.’s
 “cryptogenic infantile spasms have an unknown cause,” Id.
 at *13; (2) before administration of her four-month vac-
 cines, C.K. appeared to be clinically normal, but had an ab-
 normal brain; (3) within hours of the administration of her
 four-month vaccines, C.K. had her first infantile spasms for

    2     Dr. Zempel’s report was not included in the record
 submitted on appeal. All characterizations of his report are
 taken from the first special master’s decision, Special Mas-
 ter Decision I, 2017 WL 6601878, at *6-7, which were
 adopted by the second special master, Special Master Deci-
 sion II, 2020 WL 4197301, at*5.
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 6                                       KOTTENSTETTE v. HHS

 reasons that scientists and doctors have not been able to
 decipher; (4) C.K.’s infantile spasms have continued de-
 spite aggressive treatment and aging out of the age range
 at which infantile spasms normally abate; and (5) C.K. is
 now severely delayed in all categories and continues to suf-
 fer from infantile spasms.
      On points on which the parties and their experts disa-
 greed, the first special master made explicit findings of
 fact. First, she found credible Dr. Kinsbourne’s opinion
 that adverse reactions to DTaP “could occur, but just at a
 lower incidence than adverse reactions to whole-cell
 [DTP].” Id. She based this finding on the fact that “[p]er-
 tussis vaccine is known to be epileptogenic at times” and
 Dr. Kinsbourne’s testimony that “[a]lthough in acellular
 [DTP], the pertussis is toxoided, there is still some high-
 toxoided toxin in it.” Id. at *8. Second, she found that C.K.
 “would have fit into the Bellman study which, based on a
 week-by-week analysis, found that, among cryptogenic in-
 fantile spasms vaccinees, the onset of infantile spasms oc-
 curring within the first week after vaccination was higher
 than baseline cryptogenic infantile spasms children” and
 that the DTP vaccine “was a trigger to the onset of infantile
 spasms so that the spasms occurred sooner than they
 would have without vaccination[.]” Id. Third, she found
 that C.K., “even though she received DTaP, not [DTP],
 would have qualified to have been in the Bellman and Mel-
 chior studies because she had infantile spasms within a
 week of pertussis vaccination and the vaccination was a
 trigger, according to both the Bellman and Melchior stud-
 ies, which prompted the onset of her spasms.” Id. at *14.
 Fourth, she found that, “but for her onset of cryptogenic
 infantile spasms at four months of age, [C.K.] would have
 not had the disastrous outcome she had.” Id. Fifth, she
 found credible Dr. Kinsbourne’s testimony that the “explo-
 sive, sudden, and dramatic” onset of C.K.’s infantile
 spasms, which both experts agreed normally have an insid-
 ious onset, proved that “DTaP was a trigger of [C.K.’s]
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  KOTTENSTETTE   v. HHS                                     7

 infantile spasms.” Id. at *15. Sixth, she was “satisfied with
 the evidence in the record that the medical literature’s ac-
 ceptance of pertussis vaccine as a trigger to onset of infan-
 tile spasms in a few cases within one week of vaccination
 is sufficient to prove causation in this case, buttressed by
 the evidence of an explosive onset of infantile spasms ra-
 ther than the normal insidious onset of infantile spasms.”
 Id.
     The first special master then applied her factual find-
 ings to the three prongs set forth by this Court in Althen.
 Althen lists three prongs which petitioners must prove by
 preponderant evidence: “(1) a medical theory causally con-
 necting the vaccination and the injury; (2) a logical se-
 quence of cause and effect showing that the vaccination
 was the reason for the injury; and (3) a showing of a proxi-
 mate temporal relationship between vaccination and in-
 jury.” Althen v. Sec’y of HHS, 418 F.3d 1274, 1278 (Fed.
 Cir. 2005). The first special master concluded, based on
 her findings of fact, that: (1) “DTaP vaccine can trigger the
 onset of infantile spasms” under Althen prong 1; (2) “there
 was a logical sequence of cause and effect in DTaP causing
 [C.K.’s] onset of infantile spasms” under Althen prong 2;
 and (3) “an onset within hours of DTaP vaccination is con-
 sistent with the effect of the vaccine’s triggering an abrupt
 onset” under Althen prong 3. Special Master Decision I at
 *15. She thus ruled in favor of the Kottenstettes. Id.
      The government sought review of the first special mas-
 ter’s decision with the Court of Federal Claims. The Court
 of Federal Claims vacated and remanded, finding it “appar-
 ent from the special master’s description of the evidence
 that the petitioners’ causal theory was only plausibly
 linked to the DTaP vaccine at issue, and only plausibly
 linked to the developmental injury C.K. suffered” under Al-
 then’s first prong. Kottenstette I, 2020 WL 953484, at *3.
 According to the Court of Federal Claims, the standard
 that the first special master used to determine if the
 Kottenstettes had shown “a medical theory causally
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 8                                       KOTTENSTETTE v. HHS

 connecting the vaccination to the injury” “is not sufficiently
 distinguishable from the ‘plausible’ or ‘reasonable’ stand-
 ard that the Federal Circuit rejected in” Boatmon v. Secr’y
 of HHS, 941 F.3d 1351 (Fed. Cir. 2019). Id. The Court of
 Federal Claims rejected only one of the first special mas-
 ter’s many factual findings, determining that it was arbi-
 trary and capricious for her to accept Dr. Kinsbourne’s
 conclusion that DTP studies could apply to the DTaP for-
 mulation at lower rates without explaining why she ac-
 cepted that conclusion. Id. at *5. The Court of Federal
 Claims vacated and remanded “so that the special master
 may consider the petitioners’ theory and evidence under
 the correct legal standard.” Id. at *6.
     On remand, a different special master reweighed the
 evidence and reached the opposite conclusion. Special
 Master Decision II, 2020 WL 4197301. He denied the
 Kottenstettes’ motion to reopen the evidentiary record. Id.
 at *3. He did not hear testimony, but rather opted to rely
 on transcripts of testimony heard by the first special mas-
 ter. Id.
      Like the first special master, the second special master
 found that “C.K. was properly diagnosed with infantile
 spasms,” “that it continues to be her correct diagnosis,” and
 that C.K.’s “seizures began soon after her October 2, 2012
 vaccinations.” Id. at *4. But he disagreed with the first
 special master’s factual findings on several points, leading
 him to make his own contrary findings. First, unlike the
 first special master, he did not credit Dr. Kinsbourne’s tes-
 timony that there is a relationship between DTP and DTaP
 vaccine formulations, such that DTaP might cause adverse
 effects associated with DTP vaccination, albeit at a lower
 rate. Id. at *9. Second, he gave no weight to the Melchior
 study and minimal weight to the Bellman study. Id. at *10.
     He went on to make additional factual findings con-
 cerning the theory presented by Dr. Kinsbourne as to the
 causation of C.K.’s infantile spasms—the “two-hit model”
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  KOTTENSTETTE   v. HHS                                      9

 of epileptogenesis, in which an individual with a pre-exist-
 ing susceptibility (the first hit) experiences a stressor (the
 second hit) triggering the onset of seizures. Id. at *11. He
 found that both parties’ experts agreed that “a stressor can
 trigger a seizure generally” and that “an immune response
 can lower the seizure threshold.” Id. at *12. But he did not
 credit Dr. Kinsbourne’s testimony that this relationship be-
 tween stressors, the immune response, and the onset of sei-
 zures implicates vaccinations. Id. at *13. He did not credit
 Dr. Kinsbourne’s theory in part because of (1) Dr. Kins-
 bourne’s testimony that the innate immune response is
 both a normal and necessary part of the vaccine response
 which “occurs without negative consequences in the vast
 majority of cases;” (2) Dr. Kinsbourne’s testimony that “sci-
 entific proof is lacking” as to his theory of causation, and
 (3) Dr. Kinsbourne’s lack of qualifications as an immunol-
 ogist. Id. at*13-14.
     The second special master ultimately found that the
 Kottenstettes had failed to provide preponderant evidence
 of a “logical sequence of cause and effect showing that the
 vaccination was the reason for the injury” under Althen’s
 second prong. Id. at *15. He found that the only evidence
 that vaccinations caused C.K.’s infantile spasms was the
 timing of the spasms. Id. This was insufficient proof for
 the second special master, who noted that the govern-
 ment’s expert, Dr. Zempel, testified that fever is “by far the
 most powerful component of the immune response [] re-
 lated to a decrease in seizure threshold” and that most in-
 fantile seizures onset during the first year of life. Id. at
 *15-16.
     The second special master did not decide whether the
 Kottenstettes had shown a “medical theory causally con-
 necting the vaccination and the injury” under Althen’s first
 prong. Id. at *14. He found that the Kottenstettes had
 established a “proximate temporal relationship” between
 vaccination and injury under Althen prong three. Id. at
 *18.
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 10                                      KOTTENSTETTE v. HHS

      The Court of Federal Claims sustained the second spe-
 cial master’s decision. Kottenstette II, 2020 WL 4592590.
     The Kottenstettes timely appealed, and we have juris-
 diction pursuant to 28 U.S.C. § 1295(a)(3) and 42 U.S.C.
 § 300aa-12(f). 3
                    STANDARD OF REVIEW
     In Vaccine Act cases, this court reviews appeals from
 the Court of Federal Claims de novo. Sharpe v. Sec’y of
 HHS, 964 F.3d 1072, 1077 (Fed. Cir. 2020) (citing Lampe
 v. Sec’y of HHS, 219 F.3d 1357, 1360 (Fed. Cir. 2000)). This
 court in effect “performs the same task as the Court of Fed-
 eral Claims and reviews the special master’s legal determi-
 nations de novo, fact findings under an arbitrary and
 capricious standard, and discretionary rulings for an abuse
 of discretion.” Id. (citing Munn v. Sec’y of HHS, 970 F.2d
 863, 870-73, 870 n.10 (Fed. Cir. 1992)).
     The arbitrary and capricious standard is “difficult for
 an appellant to satisfy with respect to any issue, but par-
 ticularly with respect to an issue that turns on the weigh-
 ing of evidence by the trier of fact.” Milik v. Sec’y of HHS,
 822 F.3d 1367, 1376 (Fed. Cir. 2016) (quoting Lampe, 219
 F.3d at 1360). If the special master “‘has considered the
 relevant evidence of record, drawn plausible inferences and
 articulated a rational basis for the decision,’ then

      3  This Court has jurisdiction to review both decisions
 of the Court of Federal Claims. The Court of Federal
 Claims entered final judgment on July 27, 2020. The
 Kottenstettes timely appealed on September 17, 2020. We
 note that, although the Court of Federal Claims entered its
 order vacating the first special master’s decision on Febru-
 ary 12, 2020, that order was not a final judgment which the
 Kottenstettes could appeal to the Federal Circuit on issu-
 ance. They instead had to wait until issuance of the final
 judgment on July 27, 2020.
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  KOTTENSTETTE   v. HHS                                     11

 reversible error is ‘extremely difficult to demonstrate.’” Id.
 (quoting Hines v. Sec’y of HHS, 940 F.2d 1518, 1528 (Fed.
 Cir. 1991)). So long as a special master’s factual finding is
 based on record evidence that is “not wholly implausible,
 we are compelled to uphold that finding as not being arbi-
 trary or capricious.” Id. (quoting Cedillo v. Sec’y of HHS,
 617 F.3d 1328, 1338 (Fed.Cir.2010)). Neither the Court of
 Federal Claims nor this court should “reweigh the factual
 evidence, assess whether the special master correctly eval-
 uated the evidence, or examine the probative value of the
 evidence or the credibility of the witnesses—these are all
 matters within the purview of the fact finder.” Porter v.
 Sec’y of HHS, 663 F.3d 1242, 1249 (Fed. Cir. 2011).
                          DISCUSSION
      Petitioners seeking compensation under the Vaccine
 Act must prove by a preponderance of the evidence that a
 covered vaccine was a cause of the injury they claim. 42
 U.S.C. §§ 300aa-11(c)(1), -13(a)(1). If a petitioner’s injury
 is listed on the Vaccine Injury Table (a “Table Injury”) and
 the petitioner shows that the injury manifested within a
 specified time, causation is presumed. de Bazan v. Sec’y of
 HHS, 539 F.3d 1347, 1351 (Fed. Cir. 2008); see also 42
 U.S.C. § 300aa-11(c)(1)(C)(i). For injuries not listed on the
 Table or not occurring within the specified time, a peti-
 tioner must prove causation in fact. de Bazan, 539 F.3d at
 1351; see also 42 U.S.C. § 300aa-11(c)(1)(C)(ii). On appeal,
 the only issue before the court is whether the Kottenstettes
 have shown that vaccination caused C.K.’s non-Table in-
 jury.
     To prove that a vaccination caused a non-Table Injury,
 a petitioner must demonstrate, by a preponderance of the
 evidence:
     (1) a medical theory causally connecting the vac-
     cination and the injury; (2) a logical sequence of
     cause and effect showing that the vaccination was
     the reason for the injury; and (3) a showing of a
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 12                                      KOTTENSTETTE v. HHS

      proximate temporal relationship between vaccina-
      tion and injury.
 Althen, 418 F.3d at 1278. If a petitioner establishes a
 prima facie case of causation, the burden shifts to the gov-
 ernment to establish alternative causation by a preponder-
 ance of the evidence. Walther v. Sec’y of HHS, 485 F.3d
 1146, 1151 (Fed. Cir. 2007); see also 42 U.S.C. § 300aa-
 13(a)(1)(B). If the government fails to establish alternative
 causation, the petitioner prevails. Close calls are to be re-
 solved in favor of the petitioners. Capizzano v. Sec’y of
 HHS, 1440 F.3d 1317, 1326-27 (Fed. Cir. 2006) (quoting Al-
 then, 418 F.3d at 1280).
      The Kottenstettes argue on appeal that the Court of
 Federal Claims erred in setting aside the first special mas-
 ter’s decision, that the second special master’s decision was
 arbitrary and capricious for failing to honor the factual
 findings of the first special master, and that the second spe-
 cial master should have taken judicial notice of the alleged
 dangers of the DTaP vaccine.
      We find that both Court of Federal Claims decisions
 were in error. First, we find that the first special master
 applied the correct legal standard. Thus, the first Court of
 Federal Claims decision vacating and remanding her deci-
 sion is in error. We further find that the first special mas-
 ter’s finding that studies relating to DTP vaccination could
 apply to the DTaP formulation was not arbitrary and ca-
 pricious.
      But even if the first Court of Federal Claims decision
 was correct in finding that the first special master had ap-
 plied the wrong legal standard, we find that the second spe-
 cial master, on remand, improperly reweighed the evidence
 to come to conclusions contrary to those made by the first
 special master. Thus, we reverse the second Court of Fed-
 eral Claims decision. It is not necessary to address the
 Kottenstettes’ other arguments on appeal.
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  KOTTENSTETTE   v. HHS                                       13

      The Court of Federal Claims took two of the first spe-
 cial master’s statements out of context to find that she ap-
 plied the incorrect legal standard. First, the Court of
 Federal Claims took issue with the first special master’s
 summarization of the legal standard as a search for “med-
 ical probability rather than certainty” and her statement
 that “medical probability means biologic credibility rather
 than specification of an exact biologic mechanism.” Kotten-
 stette I, 2020 WL 953484, at *2-3. The Court of Federal
 Claims found that “biologic credibility” “is not sufficiently
 distinguishable from the ‘plausible’ or ‘reasonable’ stand-
 ard that the Federal Circuit rejected in Boatmon.” Id. at
 *3. Second, the Court of Federal Claims found that the first
 special master used an “alternative approach to proof of
 causation that fit the petitioners’ case into an existing
 study[.]” Id. But the first special master devoted over a
 page of her decision to reciting the correct legal standard.
 Special Master Decision I, 2017 WL 6601878, at *11-12. In
 the context of that statement of the legal standard and her
 application of the facts to the law, it is apparent that she
 applied the correct legal standard. Cf. Kirby v. Sec’y of
 HHS, No. 2020-2064, slip op. at 11-12 (Fed. Cir. May 19,
 2021) (finding for the petitioner where the special master,
 unlike the special master in Boatmon, did not “‘articulate[]
 a lower “reasonable” standard’ in assessing the petitioners’
 medical theory of causation,” but rather “recited the correct
 legal standard”) (quoting Boatmon, 941 F.3d at 1359)).
     The first special master’s statement that “medical
 probability means biologic credibility rather than specifica-
 tion of an exact biologic mechanism” does not set a new
 lower “biologic credibility” standard; it correctly recites this
 court’s statement in several precedential cases that proof
 of causation does not “require identification and proof of
 specific biological mechanisms[.]” Knudsen, 35 F.3d at 549;
 see also Simanski v. Sec’y of HHS, 671 F.3d 1368, 1384
 (Fed. Cir. 2012) (“Although a finding of causation ‘must be
 supported by a sound and reliable medical or scientific
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 14                                      KOTTENSTETTE v. HHS

 explanation, ‘causation’ can be found in vaccine cases . . .
 without detailed medical and scientific exposition on the
 biological mechanisms.’”). Boatmon did not, and indeed,
 could not, overrule these previous articulations of the
 standard for causation.
      The first special master also characterized in various
 ways our statement in Knudsen that “causation can be
 found in vaccine cases based on epidemiological evidence
 and the clinical picture regarding the particular child with-
 out detailed medical and scientific exposition on the biolog-
 ical mechanisms.” Knudsen v. Sec’y of HHS, 35 F.3d 543,
 549 (Fed. Cir. 1994). For example, she stated that this
 court “stated that when a vaccinee would fit within an epi-
 demiological study, that alone is sufficient proof of vaccine
 causation” before reciting the above quoted section of
 Knudsen. Special Master Decision I, 2017 WL 6601878, at
 *13. But nowhere did she apply an “alternative approach
 to proof of causation that fit the petitioners’ case into an
 existing study,” as the Court of Federal Claims found.
 Kottenstette I, 2020 WL 953484, at *3. Despite her charac-
 terization of our holding in Knudsen that fitting within an
 epidemiological study alone is sufficient proof of causation,
 she did not rely solely on the Bellman and Melchior studies
 in finding causation. Rather, she was “satisfied with the
 evidence in the record” which included, inter alia, epidemi-
 ological studies, expert testimony, and information regard-
 ing C.K.’s medical history, “that the medical literature
 acceptance of pertussis vaccine as a trigger to onset of in-
 fantile spasms in a few cases within one week of vaccina-
 tion is sufficient to prove causation in this case, buttressed
 by the evidence of an explosive onset of infantile spasms
 rather than the normal insidious onset of infantile
 spasms.” Special Master Decision I, 2017 WL 6601878, at
 *15. Finally, as discussed below, her factual findings met
 the legal standard outlined in Althen, further confirming
 that she did not apply the incorrect legal standard.
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  KOTTENSTETTE   v. HHS                                    15

     The first Court of Federal Claims decision also errone-
 ously found the first special master’s acceptance of Dr.
 Kinsbourne’s conclusion—that the DTP and DTaP formu-
 lations cause similar rare adverse effects, albeit at differ-
 ent rates—to be “[w]ithout any explanation” and therefore,
 arbitrary and capricious. Kottenstette, 2020 WL 953484, at
 *5. But the first special master did explain her finding.
 She noted, with citations to hearing testimony from Dr.
 Kinsbourne, that “[p]ertussis vaccine is known to be epilep-
 togenic at times” and that, “[a]lthough in acellular [DTP],
 the pertussis is toxoided, there is still some high-toxoided
 toxin in it.” Special Master Decision I, 2017 WL 6601878,
 at *8. She credited Dr. Kinsbourne’s testimony that recip-
 ients of DTaP may still experience adverse reactions even
 though DTaP is less reactogenic than DTP. The first spe-
 cial master, as the factfinder who actually witnessed Dr.
 Kinsbourne’s and Dr. Zempel’s live testimony, had “broad
 discretion in determining [their] credibility.” See Bradley
 v. Sec’y of HHS, 991 F.2d 1570, 1575 (Fed. Cir. 1993). That
 discretion is “virtually unreviewable” by either this court
 or the Court of Federal Claims. Id. (quoting Hambsch v.
 Dep’t of Treasury, 796 F.2d 430, 436 (Fed. Cir. 1986)).
 Thus, her determination that DTaP and DTP vaccinations
 could cause similar rare adverse effects, albeit at different
 rates, was based on record evidence that was not “wholly
 implausible.” See Lampe, 219 F.3d at 1363. She “consid-
 ered the relevant evidence of record, dr[ew] plausible infer-
 ences and articulated a rational basis for the decision.” See
 Milik, 822 F.3d at 1376 (quoting Hines, 940 F.2d at 1528).
     But even if the Court of Federal Claims did not err in
 vacating the first special master’s decision for applying the
 incorrect legal standard, we find that it erred in sustaining
 the decision of the second special master because the sec-
 ond special master improperly reweighed the evidence.
 Neither this court nor the Court of Federal Claims should
 reweigh the evidence under the arbitrary and capricious
 standard of review. See Motor Vehicle Mfrs. Ass’n of U.S.,
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 16                                      KOTTENSTETTE v. HHS

 Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43
 (1983). Nor should the second special master have re-
 weighed the evidence to come to his own factual findings
 on remand, as the government admitted at oral argument.
 Oral Arg. at 23:00-23:35, http://oralarguments.cafc.
 uscourts.gov/default.aspx?fl=20-2282_04072021.mp3. The
 Court of Federal Claims remanded for the limited purpose
 of “reconsideration under the correct legal standard[.]”
 Kottenstette I, 2020 WL 953484, at *1. The second special
 master exceeded that task on remand. He reweighed the
 facts to come to contrary findings on remand despite not
 witnessing the testimony on which he was passing judg-
 ment and despite declining to reopen the evidentiary rec-
 ord.
     Taking the factual findings expounded by the first spe-
 cial master and applying them to the Althen prongs con-
 firms her original conclusion that the Kottenstettes have
 shown by a preponderance of the evidence that C.K.’s vac-
 cination caused her injury.
      Under Althen prong one, the Kottenstettes were re-
 quired to provide “a medical theory causally connecting the
 vaccination and the injury.” Althen, 418 F.3d at 1278.
 They did so. They provided two epidemiological studies
 showing that DTP vaccination may trigger the onset of in-
 fantile spasms, which the first special master accepted and
 found informative. She further found that “[p]ertussis vac-
 cine is known to be epileptogenic at times” and that
 “[a]lthough in acellular [DTP], the pertussis is toxoided,
 there is still some high-toxoided toxin in it.” Kottenstette,
 2017 WL 6601878, at *8. She credited Dr. Kinsbourne’s
 testimony that recipients of DTaP can still experience ad-
 verse reactions even though DTaP is less reactogenic than
 DTP. As discussed above, that finding was not arbitrary
 and capricious. Finally, she found that early onset of in-
 fantile spasms, such as those triggered by four-month vac-
 cinations, could lead to worse outcomes than later onset of
 infantile spasms. We find that these facts found by the first
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  KOTTENSTETTE   v. HHS                                    17

 special master provide sufficient evidence of “a medical
 theory causally connecting the vaccination and the injury.”
 See Althen, 418 F.3d at 1278.
     Under Althen prong two, the Kottenstettes were re-
 quired to provide “a logical sequence of cause and effect
 showing that the vaccination was the reason for the in-
 jury.” Althen, 418 F.3d at 1278. They did so. As discussed
 above, the first special master found that the Kottenstettes
 had shown that both DTP and DTaP could provoke rare
 adverse events, albeit at different rates. She further found
 that C.K. was clinically normal but had an abnormal brain.
 She also found that although “the usual onset of infantile
 spasms is insidious,” the onset of C.K.’s infantile spasms
 “was explosive, sudden, and dramatic” and that abnormal
 onset confirmed that C.K.’s “vaccinations, administered
 just a few hours earlier, triggered that onset.” Special Mas-
 ter Decision I, 2017 WL 6601878, at *15. We find that these
 factual findings by the first special master provide suffi-
 cient evidence of “a logical sequence of cause and effect
 showing that the vaccination was the reason for the in-
 jury.”
     The second special master faulted the Kottenstettes for
 presenting a “mere suspicion of a temporal relationship” as
 evidence of causation under Althen prong two. Special
 Master Decision II, 2020 WL 4197301, at *15. But that is
 not an accurate characterization of the evidence. Rather,
 as the first special master found, the Kottenstettes pro-
 vided evidence that the onset of C.K.’s infantile spasms was
 unusual. Most cases of infantile spasms have an insidious
 onset. But C.K.’s spasms began “explosive[ly]” mere hours
 after her vaccinations. Kottenstette, 2017 WL 6601878, at
 *15. Thus, causation here is confirmed not just by the tem-
 poral relationship, but also by the abnormal “explosive” on-
 set. Id. That C.K.’s medical records do not show that she
 experienced other symptoms, such as fever or inflamma-
 tion, does not detract from the abnormal onset of her
 spasms or from the first special master’s other factual
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 18                                      KOTTENSTETTE v. HHS

 findings showing that C.K.’s vaccinations were a cause of
 her injury.
     Both special masters found that the Kottenstettes had
 prevailed in showing the third Althen factor, “a showing of
 a proximate temporal relationship between vaccination
 and injury.” Althen, 418 F.3d at 1278. We agree.
                         CONCLUSION
      The first special master applied the correct legal stand-
 ard and her finding that DTaP and DTP vaccinations could
 cause similar rare adverse effects, albeit at different rates,
 was not arbitrary and capricious. The second special mas-
 ter improperly reweighed the evidence on remand. And the
 first special master’s factual findings meet the standard
 propounded in Althen. Thus, we reverse both Court of Fed-
 eral Claims decisions, and reinstate the first special mas-
 ter’s finding for the Kottenstettes, including the monetary
 award set by that special master.
                        REVERSED
                            COSTS
 Costs to the Appellants.