Case: 19-1753   Document: 32     Page: 1   Filed: 04/07/2020




        NOTE: This disposition is nonprecedential.


   United States Court of Appeals
       for the Federal Circuit
                 ______________________

    TRYSTAN SANCHEZ, BY AND THROUGH HIS
    PARENTS, GERMAIN SANCHEZ, JENNIFER
                   SANCHEZ,
              Petitioners-Appellants

                            v.

       SECRETARY OF HEALTH AND HUMAN
                   SERVICES,
               Respondent-Appellee
              ______________________

                       2019-1753
                 ______________________

    Appeal from the United States Court of Federal Claims
 in No. 1:11-vv-00685-PEC, Judge Patricia E. Campbell-
 Smith.
                 ______________________

                 Decided: April 7, 2020
                 ______________________

     LISA A. ROQUEMORE, Law Offices of Lisa A. Roquemore,
 Rancho Santa Margarita, CA, argued for petitioners-appel-
 lants.

     HEATHER LYNN PEARLMAN, Vaccine/Torts Branch, Civil
 Division, United States Department of Justice, Washing-
 ton, DC, argued for respondent-appellee. Also represented
Case: 19-1753    Document: 32      Page: 2    Filed: 04/07/2020




2                                             SANCHEZ v. HHS




 by JOSEPH H. HUNT, C. SALVATORE D'ALESSIO, CATHARINE
 E. REEVES, JENNIFER LEIGH REYNAUD.
                 ______________________

    Before NEWMAN, BRYSON, and REYNA, Circuit Judges.
 BRYSON, Circuit Judge.
     This is an appeal from a decision of the Court of Fed-
 eral Claims (“the Claims Court”) reviewing the decision of
 a special master denying a petition for compensation under
 the National Vaccine Injury Compensation Program (“the
 Vaccine Act”), 42 U.S.C. § 300aa-10 et seq. Sanchez v. Sec’y
 of Health & Human Servs., 142 Fed. Cl. 247 (2019). The
 parties, the special master, and the Claims Court judge
 have all put enormous time and thoughtful attention into
 this complex and difficult case. For that reason, it is with
 reluctance that we have come to the conclusion that it is
 necessary to burden the parties and the adjudicators with
 additional work. Nonetheless, because the record has left
 certain critical issues unresolved, we are required to vacate
 the judgment and remand for further proceedings.
                               I
                              A
     Trystan Sanchez received several vaccines in February
 2009 when he was six months old. Shortly after his vac-
 cinations, he developed a fever and displayed what his par-
 ents characterized as “inconsolable crying.” Several days
 later, he again developed a fever and was congested. He
 was diagnosed at that time with a common cold.
     In August 2009 Trystan received a second round of vac-
 cinations. Trystan’s mother reported at that time that she
 had noticed a change in Trystan’s development. A neurol-
 ogist who saw Trystan in November 2009 determined that
 he was exhibiting global developmental delays. Trystan
 continued to show developmental delays for the next sev-
 eral years.
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 SANCHEZ v. HHS                                              3



      In 2011, suspecting that the 2009 vaccinations had
 been responsible for Trystan’s developmental difficulties,
 the Sanchezes filed a petition for compensation under the
 Vaccine Act. While the petition was pending, Trystan un-
 derwent genetic testing. Based on two mutations in
 Trystan’s DNA discovered during that testing, Trystan was
 diagnosed with Leigh’s syndrome. Leigh’s syndrome is a
 rare but severe genetic disorder that typically manifests it-
 self in the first year of life and causes progressive loss of
 mental and physical abilities, usually resulting in early
 death.
                               B
     Prior to Trystan’s genetic testing and his Leigh’s syn-
 drome diagnosis, the special master who was assigned to
 the case held a hearing to determine the facts relating to
 Trystan’s condition. Based on the evidence at the hearing
 and the parties’ joint statement of stipulated facts, the spe-
 cial master then entered a detailed Ruling Finding Facts
 in April 2013. In several instances in his factual findings,
 the special master chose to credit the written medical re-
 ports’ descriptions of Trystan’s symptoms over the testi-
 mony of Trystan’s parents.
     The special master found that Trystan appeared
 healthy and was developing normally before February 5,
 2009, when he received his first round of vaccines. Shortly
 after his pediatric visit that day, however, Trystan began
 to cry inconsolably, he ran a temperature of 102.2, and he
 developed a lump on his left thigh that was hot to the touch.
 The fever ebbed and flowed over the next several days.
     On February 15, Trystan became congested and began
 running a fever again. The following night, his fever be-
 came worse, and he began what his mother described as
 “loud, high-pitched” crying. His father sought to calm
 Trystan by holding him, but when Trystan would fall
 asleep, he would repeatedly startle awake. According to
 his father, Trystan “kept kicking his feet and jerking
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4                                                SANCHEZ v. HHS




 around” in his father’s arms, “almost as if he didn’t want to
 be held.” His father testified that Trystan was “jerking his
 body” and “holding his arm behind his back kind of in an
 uncomfortable position.” Trystan’s father said that when
 he “went to put [Trystan’s] arm back to the normal posi-
 tion,” he could “feel that he had a lot of tension in that arm.
 And when I did put it back, his arm went right back holding
 it back towards the back of his body.” In his 2013 Ruling
 Finding Facts, the special master did not appear to credit
 Trystan’s father’s testimony regarding Trystan’s arm
 movements. In that ruling, the special master said that
 “[a]t this time, Trystan did not begin to exhibit arm contor-
 tions.”
     The following morning, Trystan’s mother took Trystan
 to the pediatrician’s office, where he was examined by Jon-
 athan P. Luna, a certified physician’s assistant. Mr. Luna
 diagnosed Trystan with a “common cold” and “viral syn-
 drome.” Ms. Sanchez testified that she told Mr. Luna about
 Trystan’s arm contortions, but Mr. Luna did not make a
 note of her observations in his record of the visit. In light
 of the absence of a report of the arm contortions in Mr.
 Luna’s record of the visit, the special master found that
 Trystan did not begin to exhibit arm contortions at that
 time.
      Trystan suffered from coughing and congestion episod-
 ically for the next couple of months. Ms. Sanchez testified
 that during that period, Trystan continued to have arm
 contortions, sometimes several times a day. In addition,
 she testified that Trystan “started to lose control of his
 head,” that his “trunk . . . was not as strong,” that he “didn’t
 have any eye contact,” and that he “didn’t want to play”
 anymore. Again, however, the special master did not credit
 Ms. Sanchez’s testimony because it was not corroborated
 by medical reports.
    On April 29, 2009, after Trystan had suffered from a
 cough and congestion for two weeks, his mother took him
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 SANCHEZ v. HHS                                               5



 to a pediatrician, Dr. Nabil R. Seleem. She testified that
 she told Dr. Seleem about Trystan’s arm contortions. Dr.
 Seleem, however, did not note any such comments in his
 record of the visit, and his notes reflect his observation that
 Trystan appeared to be neurologically normal. Based on
 Dr. Seleem’s report, the special master found that Ms.
 Sanchez did not report any “unusual arm movements or
 developmental issues” to Dr. Seleem. Dr. Seleem diag-
 nosed Trystan with an ear infection and bronchitis, for
 which he prescribed an antibiotic.
     Trystan returned to the clinic on May 13, 2009, at
 which time the examining pediatrician, Dr. Philip S.
 Brown, noted that Trystan’s infection seemed to be resolv-
 ing. Ms. Sanchez testified that she told Dr. Brown about
 “the weird movement, the contortion of the arm,” and the
 issue with Trystan’s head control. Dr. Brown’s report of
 the visit did not include any reference to those neurological
 complaints, however, and the special master found that
 Trystan had not experienced any loss of skills at that point.
      On August 17, 2009, Trystan was seen by physician’s
 assistant Micaela Marin-Tucker for his one-year well-baby
 exam. Ms. Marin-Tucker’s notes reflect that Trystan’s
 mother said she had noticed a change in Trystan’s develop-
 ment about two to three months earlier. Ms. Sanchez tes-
 tified that Ms. Marin-Tucker’s notes were wrong and that
 she told Ms. Marin-Tucker she had noticed a change in
 Trystan’s development that began five to six months ear-
 lier. The special master credited Ms. Marin-Tucker’s con-
 temporary notes over Ms. Sanchez’s testimony and found
 that Trystan began to lose skills only as of about the begin-
 ning of May 2009 at the earliest.
     In the course of her examination, Ms. Marin-Tucker
 found that Trystan did not walk, stand, crawl, and hold his
 head up while sitting. She also found that Trystan did not
 attempt to move his lower extremities, and she noticed that
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6                                              SANCHEZ v. HHS




 his extremities seemed generally soft, but rigid at times.
 Ms. Marin-Tucker referred Trystan to a neurologist.
     During the August 2009 clinic visit, Trystan received
 another round of vaccinations. Following those vaccina-
 tions, Ms. Sanchez testified, Trystan “got sick again” and
 “started contorting his arm even more.”
     Six weeks later, Trystan returned to the clinic for a fol-
 low-up visit. At that time, Ms. Marin-Tucker noted that
 Trystan had “no seizures, weakness, or tics.” In the report
 of her neurological examination, however, she stated that
 Trystan was “unable to grasp, sit, crawl, or make much eye
 contact.” She again urged the family to have Trystan ex-
 amined by a neurologist.
     In November of that year, Trystan was seen by a neu-
 rologist. Prior to that visit, Trystan began having tremors
 or twitching of his whole body. The neurologist recorded
 reports that Trystan was unable to sit independently, his
 hands stayed closed, and his feet went forward when he
 was at rest. His examination was positive for muscle
 spasms, weakness, and global developmental delay, among
 other problems. Based on his examination and Trystan’s
 history, the neurologist concluded that Trystan was suffer-
 ing from “global developmental delay of unclear etiology,
 though a genetic predisposition is suspected based on the
 family history and a [central nervous system] cause is sug-
 gested by the physical exam findings.” An MRI performed
 in December 2009 revealed abnormalities in Trystan’s ba-
 sal ganglia, and the treating physicians began to suspect a
 metabolic disorder.
     During the ensuing five years, Trystan was examined
 on numerous occasions, without a firm diagnosis being
 reached. Genetic testing in December 2014, over a year af-
 ter the special master’s initial factual findings, revealed
 that Trystan had two mutations in his SDHA gene. Based
 on those mutations, Trystan’s treating physician confirmed
 a diagnosis of Leigh’s syndrome.
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 SANCHEZ v. HHS                                             7



                              C
     Following Trystan’s diagnosis with Leigh’s syndrome,
 the petitioners’ theory changed. Rather than arguing that
 the vaccines directly caused his condition, they acknowl-
 edged that Trystan’s Leigh’s syndrome was the product of
 his genetic condition. They argued, however, that the first
 round of vaccinations Trystan received on February 5,
 2009, either caused his genetic condition to be expressed or
 significantly aggravated the course of his disease. They
 also argued that Trystan’s second set of vaccinations, on
 August 17, 2009, further aggravated the effects of his dis-
 ease.
     To address these issues, the special master held a sec-
 ond hearing in December 2017 at which experts for the par-
 ties testified. At that four-day hearing, two experts
 testified for the petitioners—Dr. Lawrence Steinman and
 Dr. Dmitriy Niyazov. Four experts testified for the govern-
 ment—Dr. Gerald Raymond, Dr. Stephen McGeady, Dr.
 Edward Cetaruk, and Dr. Dean Jones.
     The petitioners’ experts testified that Trystan’s devel-
 opmental regression began shortly after his first vaccina-
 tions on February 5, 2009. Dr. Niyazov testified that the
 symptoms Trystan experienced immediately after receiv-
 ing those vaccines were evidence of an immune response.
 Because of Trystan’s genetic mutations, which resulted in
 decreased mitochondrial function, the vaccines started an
 inflammatory response affecting Trystan’s brain. That re-
 sponse, according to Dr. Niyazov, “triggered a gradual pro-
 cess of developmental regression” that became more
 evident around June 1, 2009.
     Dr. Steinman similarly testified that the vaccines
 stressed the energy sources in Trystan’s cells. Because of
 Trystan’s mitochondrial disease, Dr. Steinman testified,
 Trystan was “on the edge all the time, and this vaccine trig-
 ger[ed] a downward cascade that began on February 5th
 when he got the vaccine.” Dr. Steinman and Dr. Niyazov
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8                                              SANCHEZ v. HHS




 testified that Trystan’s inconsolable high-pitched crying
 and his jerking and arm contortions were evidence of neu-
 rodegenerative events, and were not consistent with a com-
 mon cold.
      Drs. Niyazov and Steinman also testified that Trystan
 suffered what is known as a “challenge-rechallenge.” That
 is, his regression and dystonia following his initial vaccina-
 tions was repeated following his August 2009 vaccinations,
 except that his condition worsened significantly after that
 time. Dr. Steinman referred to the aftermath of Trystan’s
 second set of vaccines as “an accelerated neurological de-
 generation due to a recall response.” Dr. Niyazov agreed
 that the second set of vaccinations set Trystan back again.
     One of the government’s experts, Dr. McGeady, testi-
 fied that while Trystan’s inconsolable crying on the day of
 his initial vaccinations “may very well have been” a re-
 sponse to the vaccines, the fever that he ran on February
 16, 2009, was caused by the viral respiratory infection he
 suffered at that time. The other principal government ex-
 pert, Dr. Raymond, testified that in his opinion, the evi-
 dence did not show that Trystan had a seizure on February
 16. Instead, he testified that “[k]icking of the legs, resist-
 ing being held, is not, in my opinion, epileptic activity.”
      Following the December 2017 hearing, the special ma-
 ter entered his Published Decision Denying Compensation.
 In that detailed order, he reviewed his earlier factual find-
 ings and then turned to deciding the issue of compensation
 in light of the expert evidence adduced at the second hear-
 ing.
     At the outset, the special master addressed the first of
 the three factors to be considered in assessing a vaccine
 compensation claim under this court’s decision in Althen v.
 Secretary of Health & Human Services, 418 F.3d 1274,
 1278 (Fed. Cir. 2005): whether the petitioners have shown
 “a medical theory causally connecting the vaccination and
 the injury.” In this case, that factor required the special
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 SANCHEZ v. HHS                                            9



 master to determine whether the petitioners had shown
 that the vaccines Trystan received could have caused the
 manifestation or aggravation of his Leigh’s syndrome.
      After reviewing the expert testimony and the medical
 literature, the special master concluded that “though a link
 between vaccination and the onset of Leigh’s syndrome has
 not been established to the standard of medical certainty,”
 the evidence presented was “sufficient to conclude that the
 Sanchezes’ theory is plausible insofar as it is consistent
 with contemporary understanding of the biological systems
 at play.” The special master explained that the “first man-
 ifestation of Leigh’s syndrome is known to follow an inter-
 current illness in many, if not most, cases.” In particular,
 the special master concluded that the Sanchezes had pre-
 sented “a plausible medical theory explaining how
 Trystan’s vaccines may have caused his injury” by showing
 that it was more plausible than not that the vaccine that
 Trystan received “is known to sometimes cause fever,” and
 that “fever can cause decompensation in someone with a
 pre-existing mitochondrial disease.” 1 In light of the evi-
 dence before him, the special master concluded that the
 government had not rebutted either of those theories, and
 “that both premises are likely to be consistent with contem-
 porary medical thought.”
     The special master then turned to the question
 whether the vaccine had in fact triggered or aggravated
 Trystan’s Leigh’s syndrome, for which his genetic muta-
 tions predisposed him. The special master noted that the
 petitioners and their experts argued that Trystan’s neuro-
 logical deterioration began on February 5, 2009, the day he
 received his vaccinations. The special master concluded,
 however, that the evidentiary record “does not support this


    1  As the special master explained, “decompensation” is
 a period of regression or loss of skills frequently seen in
 children with Leigh’s syndrome.
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 10                                           SANCHEZ v. HHS




 premise that is so central to the Sanchezes’ argument.” In-
 stead, the special master found that “approximately three
 months passed between when Trystan received the Febru-
 ary 5, 2009 vaccinations and the earliest possible onset of
 his neurological regression.” Based on that finding, the
 special master asked whether a delay of that magnitude “is
 consistent with vaccine-causation.” In light of the medical
 literature in evidence, he concluded that it was not. In-
 stead, summarizing the literature, the special master con-
 cluded that regression would generally be expected to occur
 in such patients within about two weeks or less after the
 triggering event, such as a fever or infection.
     The special master made a series of factual findings
 bearing on the issue. In particular, he found that in the
 hours after the February 5 vaccination, Trystan developed
 a fever and displayed inconsolable crying. The fever ebbed
 and flowed for a few days.
     The special master found that the vaccines Trystan
 was given on February 5 caused him to develop a fever. He
 also found that fever, including fever following vaccination,
 can cause decompensation in a patient with a metabolic
 disease such as Trystan’s.
      On February 15, Trystan developed another fever and
 was crying inconsolably again. He “was congested and had
 difficulty breathing.” In addition, the special master found,
 Trystan’s “arms contorted and he was jerking around.”
 However, the special master found that those movements
 “were of the type typically displayed by an infant suffering
 from a cold.” The special master also found that Trystan’s
 family did not convey to physician’s assistant Luna, who
 examined Trystan the following day, that Trystan had dis-
 played any symptoms consistent with a neurological injury
 as opposed to a cold, and Mr. Luna did not detect any signs
 in the course of his examination that were consistent with
 a neurological injury as opposed to a cold.
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 SANCHEZ v. HHS                                             11



     The special master also found that Trystan’s parents
 took him to see Dr. Seleem on April 29, 2009, because of
 concern about his cough and congestion that had lasted for
 two weeks, and that they did not convey to Dr. Seleem that
 Trystan had displayed any symptoms consistent with a
 neurological injury. The special master further found that
 Dr. Seleem did not observe any signs that were indicative
 of neurological injury during the examination he performed
 on Trystan.
     Finally, the special master credited the report pre-
 pared by physician’s assistant Marin-Tucker, who stated
 that Trystan’s mother had said during the August 17, 2009,
 visit that Trystan first started showing signs of loss of
 skills approximately two to three months earlier. Based on
 that evidence, the special master concluded that the first
 signs of Trystan’s loss of skills occurred by the beginning of
 May 2009 at the earliest.
     The special master then addressed the question
 whether the delay between the date of the vaccinations and
 when Trystan’s parents noticed his loss of skills was at-
 tributable to the fact that in a child as young as Trystan,
 the loss of skills may not be immediately obvious. Based
 on the literature, the special master found that “there is
 some truth to that claim.” In addition, the special master
 deemed that there is “a non-insignificant chance that the
 Sanchezes relayed a concern [about Trystan’s develop-
 ment] at the May 13, 2009, visit with Dr. Brown that did
 not end up in the records.” Nonetheless, the special master
 concluded, that possibility did not account for the three-
 month period during which the medical records “show[ed]
 no indication of Trystan having, or the parents being con-
 cerned about, a neurological condition.” Instead, the spe-
 cial master found, the parents “appeared to be focused on
 Trystan’s multiple colds.”
     The special master acknowledged that “if Trystan did
 not experience any other decompensating events between
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 12                                           SANCHEZ v. HHS




 the vaccination and the onset of his Leigh’s syndrome, it
 may very well make his parents’ claims of causation less
 improbable.” However, the special master pointed out that
 during the three months “leading up to when his loss of
 skills first manifested, Trystan suffered from multiple up-
 per respiratory infections.” Such infections, the special
 master noted, “are known to precipitate mitochondrial de-
 compensation.” Trystan’s upper respiratory infections be-
 tween March and May of 2009, the special master
 concluded, “are entirely consistent with the infections be-
 ing the intercurrent infection that induced his metabolic
 decompensation . . . .”
      The special master further stated that the petitioners’
 failure to address “a conspicuous and probable alternate
 cause for the manifestation of Trystan’s Leigh’s syndrome
 weighs against a finding that the vaccination caused
 Trystan’s injury.” He determined that the presence of a
 probable alternative cause, “in combination with the un-
 likelihood of a multiple-month delay between the vaccine
 and the onset of his neurodegeneration, makes a finding
 that the vaccine was, more likely than not, a substantial
 factor in Trystan’s Leigh’s syndrome untenable.” The spe-
 cial master therefore denied the petition for compensation.
                              D
     The petitioners filed a motion for review of the special
 master’s decision with the Claims Court. After conducting
 a detailed review of the evidence and the special master’s
 findings, the court upheld the special master’s decision
 denying compensation.
     The Claims Court rejected petitioners’ contention that
 the special master had erred in finding that Trystan’s vac-
 cine-related injury occurred within an acceptable time
 frame. The court declined the petitioners’ “invitation to re-
 weigh the evidence as to disease onset,” because nothing in
 the allegations of fact or the expert opinions relied on by
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 SANCHEZ v. HHS                                             13



 the petitioners showed that the special master’s findings as
 to disease onset were arbitrary or capricious.
      The Claims Court also rejected the petitioners’ argu-
 ment that the special master had ignored their “challenge-
 rechallenge” argument based on the combined effect of the
 February and August 2009 vaccinations. The court found
 that the special master had “weighed the relevant evidence
 of rechallenge symptoms” but “found the evidence to be un-
 persuasive.” For that reason, the court concluded, “it was
 not error for the special master to also find petitioners’ ex-
 pert testimony as to rechallenge to be so unpersuasive as
 to be unworthy of mention . . . .”
                               II
      On appeal, the petitioners challenge the special mas-
 ter’s decision (and the Claims Court’s affirmance of that
 decision) on three principal grounds. First, the petitioners
 contend that the rulings of the special master and the
 Claims Court are contrary to the 2015 decision of this court
 in Paluck v. Secretary of Health & Human Services, 786
 F.3d 1373 (Fed. Cir. 2015). Second, they argue that the
 central component of the special master’s ruling—that
 Trystan’s Leigh’s syndrome was not triggered by his Feb-
 ruary 5, 2009, vaccinations—is contrary to the evidence.
 Third, they argue that the special master failed to address
 their “challenge-rechallenge” argument, i.e., their conten-
 tion that the combination of the first vaccination in Febru-
 ary 2009, and the second vaccination, in August 2009,
 triggered or aggravated Trystan’s condition.
     We are mindful that our authority to review factual
 findings made by the special master is extremely limited.
 As this court explained in Paluck, 786 F.3d at 1378, “we
 review findings of fact under the arbitrary and capricious
 standard.” See also Porter v. Sec’y of Health & Human
 Servs., 663 F.3d 1242, 1249 (Fed. Cir. 2011).
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 14                                            SANCHEZ v. HHS




                               A
     In Paluck, we affirmed the Claims Court’s decision
 overturning a special master’s denial of compensation to
 Vaccine Act claimants in circumstances similar in several
 respects to this case. We agree with the petitioners that
 this case has some features in common with Paluck, and
 that this court’s analysis in Paluck provides helpful guid-
 ance for the analysis of the merits of the petitioners’ claims
 in this case.
     Like this case, Paluck involved a child with a mitochon-
 drial disorder. And, as in this case, the evidence in Paluck
 showed that vaccines can activate the immune system,
 which in an individual with a mitochondrial disease can
 result in oxidative stress that can, in turn, cause progres-
 sive neurological deterioration over time. See Paluck, 786
 F.3d at 1380–81. In fact, several of the scientific papers
 that the courts in Paluck pointed to as supporting the
 Palucks’ theory of liability were introduced by the
 Sanchezes in this case.
      While there are similarities between this case and
 Paluck, there are differences as well, and because of those
 differences, this case cannot be decided based on Paluck
 alone. In particular, the Claims Court in Paluck rejected
 the special master’s conclusion that the child’s post-vac-
 cination deterioration did not align with the medical theory
 on which the petitioners relied, in that the regression was
 not “linear” and the child did not manifest identifiable
 symptoms of neurologic injury within three weeks of his
 vaccinations. The court sustained the Claims Court’s rul-
 ing that the special master’s decision was arbitrary and ca-
 pricious in that respect; the Claims Court held that the
 special master disregarded significant probative evidence
 that the child “experienced rapid and progressive neurolog-
 ical deterioration within a medically acceptable interval
 following his vaccinations.” 786 F.3d at 1380. In light of
 the “compelling evidence of post-vaccination neuro-
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 SANCHEZ v. HHS                                             15



 developmental regression,” this court concluded that the
 special master had “no reasonable basis for concluding that
 [the child] did not experience the progressive neurodegen-
 eration predicted” by the petitioners’ medical theory. Id. at
 1382.
     This court in Paluck also concluded that the special
 master had erred by “setting a hard and fast deadline of
 three weeks between vaccination and the onset of clinically
 apparent symptoms of neurological injury,” which the court
 found was not supported by the medical literature in evi-
 dence. Id. at 1382–83. The court also found several of the
 inferences from the evidence drawn by the special master
 to be unsupported, and it concluded that the special master
 had improperly disregarded MRI evidence indicating pro-
 gressive neurodegeneration and contemporaneous state-
 ments from the child’s treating physicians. Id. at 1384–86.
      In this case, unlike in Paluck, the special master did
 not adopt a strict time limit or a requirement of “linearity”
 for the manifestation of signs of Trystan’s neurological re-
 gression. Instead, the special master considered the period
 of time, together with the other evidence of the progression
 of Trystan’s disease, in attempting to determine the issue
 of causation. Nor did the special master draw the improper
 inferences noted by this court in Paluck or disregard med-
 ical evidence or the observations of the treating physicians.
 In fact, the special master in this case relied heavily on the
 observations (or the absence of observations) by the treat-
 ing physicians in determining whether to credit the testi-
 mony given by Trystan’s parents. In sum, while there are
 substantial parallels between this case and Paluck, the dif-
 ferences between the two cases are such that the outcome
 of this case is not dictated by Paluck.
                               B
    We next turn to the petitioners’ challenge to the special
 master’s causation analysis. That issue requires a close ex-
 amination of the evidence in the record.
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 16                                            SANCHEZ v. HHS




      The special master found the vaccines Trystan received
 on February 5, 2009, are known to cause fever, and fever
 can cause neural decompensation in someone with a preex-
 isting mitochondrial disease. The special master concluded
 that Trystan clearly suffered a loss of skills after receiving
 the vaccine, and that the loss of skills was the manifesta-
 tion of his Leigh’s syndrome. The critical finding made by
 the special master as to the effect of the vaccination, how-
 ever, was that the period of time between the vaccinations
 in February 2009 and Trystan’s loss of skills no earlier
 than May 2009 was too long for the vaccinations to have
 been the likely trigger for his Leigh’s syndrome. It is that
 finding that is the principal focus of the petitioners’ chal-
 lenge to the special master’s ruling.
     In support of their argument on causation, the petition-
 ers point to testimony from their experts that Trystan’s fe-
 ver and inconsolable crying were evidence of the onset of
 neurodegeneration, and that Trystan’s arm contortions on
 February 16, 2009, only 11 days after his vaccinations,
 were also indicative that he had suffered an adverse neu-
 rological event.
     The special master rejected that argument, in large
 part because he concluded that Trystan was diagnosed
 with a cold on February 17, and that his symptoms the
 night before were of the type typically displayed by infants
 suffering from a cold. The petitioners do not challenge the
 finding that Trystan was suffering from a cold, but they
 contend that the evidence shows that he was also suffering
 from a neurological injury at that time. In particular, the
 petitioners dispute the special master’s finding that
 Trystan’s symptoms—his arm contortions in particular—
 were symptoms of a cold. That finding, they contend, is
 wholly lacking in record support.
     Analyzing this issue is complicated by the manner in
 which the special master made factual findings relating to
 the events of February 16, 2009. In his 2013 Ruling
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 SANCHEZ v. HHS                                           17



 Finding Facts, the special master found that although
 Trystan “kept kicking his feet and jerking around” in his
 father’s arms on that evening, he “did not begin to exhibit
 arm contortions” at that time, and he “did not exhibit arm
 contortions” between that time and the time Ms. Sanchez
 took him to the doctor in late April 2009. In the 2018 Pub-
 lished Decision Denying Compensation, however, the spe-
 cial master found that on that evening, Trystan’s “arms
 contorted and he was jerking around.”
     That discrepancy is significant. The government’s ex-
 pert witnesses, testifying based on the special master’s
 2013 findings, said that the symptoms exhibited by
 Trystan on the night of February 16, 2009—inconsolable,
 high-pitched crying and “jerking around” in his father’s
 arms—were consistent with a cold and were not indicative
 of a seizure. However, the government’s witnesses did not
 have before them the special master’s later finding that
 Trystan’s arm contortions began as early as February 16.
 Moreover, if the special master’s 2018 finding was based on
 the testimony of Trystan’s father, it seems plausible that
 Mr. Sanchez’s testimony—that Trystan repeatedly held his
 arm behind his back and kept returning it to that posi-
 tion—could be regarded as evidence of a seizure or dysto-
 nia, as the petitioners’ expert Dr. Steinman testified. And
 a seizure or dystonia at that time, Dr. Steinman testified,
 “could be evidence of brain damage.”
      Importantly, because of the change in the findings
 made with respect to the arm contortions, the special mas-
 ter’s finding that Trystan’s behavior on the night of Febru-
 ary 16 was consistent with a cold is not supported by expert
 testimony that specifically addressed the arm contortions.
 Because this issue is of central importance to the causation
 analysis, it is necessary to remand for further considera-
 tion of the causation issue in light of the special master’s
 findings in 2018 regarding Trystan’s arm contortions.
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 18                                            SANCHEZ v. HHS




     A related issue that the special master should consider
 on remand has to do with the application of the second and
 third Althen factors: “(2) a logical sequence of cause and ef-
 fect showing that the vaccination was the reason for the
 injury, and (3) a showing of a proximate temporal relation-
 ship between vaccination and injury.” Althen, 418 F.3d at
 1278. The special master treated those two factors to-
 gether as being directed to the single issue of causation, on
 which the petitioners bore the burden of proof. While it is
 true that the entire Althen test is generally directed to the
 issue of causation, Althen distinguishes between the three
 factors that are necessary to make out a prima facie case
 (on which the petitioners bear the burden of proof) and the
 question whether the injury was caused by factors unre-
 lated to the vaccine (on which the government bears the
 burden of proof). If petitioners make a prima facie case un-
 der the first three factors, they are entitled to prevail un-
 less the government shows, by a preponderance of the
 evidence, that the injury was in fact caused by factors un-
 related to the vaccine. Althen, 418 F.3d at 1278; see
 Shalala v. Whitecotton, 514 U.S. 268, 270–71 (1995); 42
 U.S.C. § 300aa-13(a)(1)(B).
     In this case, there is no question that Trystan suffered
 neurodegeneration beginning no later than May or June of
 2009. But for the cold he suffered on February 16, 2009,
 and the other infections he suffered during the spring of
 that year, the vaccinations might have been prime suspects
 as the triggering mechanism for his mitochondrial disease
 to manifest itself. To be sure, there was a several-month
 delay between the initial vaccines and the time the special
 master found that Trystan’s loss of skills began to be no-
 ticed. But that delay, by itself, was not necessarily dispos-
 itive. As the special master noted, there is some force to
 the point that in a child as young as Trystan, loss of skills
 would not be immediately noticed.
     For that reason, it is important for the special master
 to make explicit findings as to two separate issues: (1)
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 SANCHEZ v. HHS                                             19



 whether there was a logical sequence of cause and effect
 linking Trystan’s vaccinations and his injuries as well as a
 proximate temporal relationship between the vaccinations
 and the onset of the injuries; and (2) whether Trystan’s in-
 fections between February and May of 2009 caused the
 manifestation of his Leigh’s syndrome, independent of his
 vaccinations. If the special master finds that the petition-
 ers have not met their burden as to the first issue, it is un-
 necessary for the special master to address the second
 issue. But if the special master finds that the petitioners
 have met their burden of establishing a prima facie case as
 to the first issue, he must determine whether the govern-
 ment has met its burden as to the second.
                               C
     The petitioners also contend that the special master
 did not address the “challenge/rechallenge” claim raised by
 the petitioners’ experts. That theory of causation was that
 the combined effect of the February and August vaccina-
 tions caused or aggravated Trystan’s condition. Although
 that issue was raised in the petitioners’ pre-hearing brief
 and by the evidence, the special master did not address
 that theory in his Published Decision Denying Compensa-
 tion.
      On review of the special master’s ruling, the Claims
 Court held that it was not necessary for the special master
 to address that issue expressly, in that the argument ap-
 peared to have been implicitly rejected in the special mas-
 ter’s factual findings. However, the findings that the
 special master made in his Ruling Finding Facts predated
 the testimony of the petitioners’ experts, much of which fo-
 cused on the challenge/rechallenge theory. Moreover, the
 special master based his factual conclusion that Trystan’s
 condition did not deteriorate after the August 2009 vac-
 cinations on the fact that the contemporaneous medical
 records did not corroborate the Sanchezes’ testimony to
 that effect. The record closest in time to the August
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 20                                           SANCHEZ v. HHS




 vaccinations was the record prepared by Ms. Marin-Tucker
 regarding the August 17, 2009, visit when Trystan received
 his vaccinations. Based on that report the special master
 found that Trystan could not stand, walk, crawl, or hold his
 head up while sitting.
     Six weeks later, when Trystan returned to the clinic for
 a follow-up visit. Based on Ms. Marin-Tucker’s report for
 that visit, the special master found that Trystan was “un-
 able to grasp, sit, crawl, or make much eye contact.” While
 the two medical reports are generally similar, the special
 master’s findings with regard to the two reports suggest
 that Trystan may have suffered at least some additional
 loss of skills during the period between August and October
 2009, an issue the special master did not expressly address.
      The challenge/rechallenge theory is not frivolous, and
 does not appear to have been implicitly rejected. For those
 reasons, we conclude that the special master should ad-
 dress that theory expressly on remand and decide whether
 it supports compensation in this case.
                              D
     Finally, it may be necessary for the special master to
 address a question that was left open in the last two pages
 of the special master’s decision denying compensation:
 whether the Secretary showed, because of Trystan’s muta-
 tions, the timing and severity of his Leigh’s syndrome
 would have been the same, regardless of the effect of the
 vaccinations.
     This is a difficult issue on which the science has been
 developing rapidly. Each party’s experts testified on this
 issue at the December 2017 hearing. In light of the speed
 with which medical understanding of the course of genetic
 disorders such as Leigh’s syndrome has been expanding,
 however, the special master on remand may wish to give
 the parties an opportunity to supplement the record with
 any relevant medical research or reports postdating the
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 SANCHEZ v. HHS                                         21



 hearing held by the special master two and one-half years
 ago.
     For the reasons given, we vacate the judgment in this
 case and remand for further proceedings consistent with
 this opinion.
     No costs.
                 VACATED AND REMANDED
