Nikko Cerrone v. Secretary of Health and Human Services

United States Court of Appeals
for the Federal Circuit
______________________
NIKKO CERRONE,
Petitioner-Appellant
v.
SECRETARY OF HEALTH AND HUMAN
SERVICES,
Respondent-Appellee
______________________
2024-1281
______________________
Appeal from the United States Court of Federal Claims
in No. 1:17-vv-01158-EGB, Senior Judge Eric G. Bruggink.
______________________
Decided: July 29, 2025
______________________
G ARY A. K ROCHMAL, Gary A. Krochmal, PLLC, Farm-
ington Hills, MI, argued for petitioner-appellant. Also rep-
resented by AMBER WILSON , Wilson Science Law,
Washington, DC.
ELEANOR H ANSON , Torts Branch, Civil Division, United
States Department of Justice, Washington, DC, argued for
respondent-appellee. Also represented by C. SALVATORE
D’ALESSIO , LARA A. ENGLUND , M ALLORI B ROWNE
O PENCHOWSKI, H EATHER LYNN PEARLMAN , Y AAKOV ROTH .
______________________
Case: 24-1281 Document: 39 Page: 1 Filed: 07/29/2025

-- 1 of 16 --

CERRONE v. HHS 2
Before M OORE, Chief Judge, LOURIE and BRYSON , Circuit
Judges.
BRYSON , Circuit Judge.
Nikko Cerrone filed a petition for compensation under
the National Vaccine Injury Compensation Program, 42
U.S.C. §§ 300aa-10–300aa-34 (“Vaccine Act”), claiming
that the administration of certain vaccines caused him to
develop ulcerative colitis (“UC”), a type of inflammatory
bowel disease (“IBD”). The special master assigned to his
petition denied his claim for compensation, and the Court
of Federal Claims upheld that decision. We affirm.
I
A
On October 7, 2015, Mr. Cerrone, who was sixteen
years old at the time, visited his primary care physician
complaining of jaw and ear pain. At that visit, he received
the Gardasil human papillomavirus (“HPV”) vaccine, the
Flumist influenza vaccine, and the Hepatitis A vaccine.
App. 2. No reaction to the vaccines was recorded on that
day or for the remainder of 2015. Id. However, Mr. Cer-
rone later stated in an affidavit that in November 2015 his
stamina and stability decreased, and in December 2015 he
first experienced blood in his stools. Id.
On February 10, 2016, Mr. Cerrone returned to his
physician complaining of a sore throat and congestion.
App. 3. At that visit, he received a second dose of the HPV
vaccine. Id. Although his medical records from that visit
do not mention any gastrointestinal issues, he visited the
emergency room three days later, complaining that he had
been experiencing blood in his stools for three weeks and
that his symptoms had worsened in the past several days.
Id. Mr. Cerrone then underwent various diagnostic tests,
and on March 24, 2016, he was diagnosed with UC. Id.
Case: 24-1281 Document: 39 Page: 2 Filed: 07/29/2025

-- 2 of 16 --

CERRONE v. HHS 3
On May 19, 2016, Mr. Cerrone returned to the emer-
gency room to be treated for UC symptoms, and he reported
that he had been experiencing symptoms for five months.
App. 4. He began treatment for UC at around that time.
Id. On June 24, 2016, he returned to his physician for more
testing and received his third dose of the HPV vaccine. Id.
No reaction to that vaccination was documented, and Mr.
Cerrone has not alleged that the third dose of the HPV vac-
cine exacerbated his symptoms. Id.
On October 3, 2016, Mr. Cerrone was further evaluated
for UC. Id. At that time, he reported that his symptoms
had begun in December 2015. Id. Since October 2016, Mr.
Cerrone has received treatment for UC and has periodi-
cally experienced acute exacerbation of his symptoms.
App. 5.
B
On August 28, 2017, Mr. Cerrone filed a petition seek-
ing compensation under the Vaccine Act for his alleged vac-
cine-related injury. App. 1. The case was assigned to the
Chief Special Master of the National Vaccine Injury Com-
pensation Program, who heard expert testimony from Da-
vid Rosenstreich and John Santoro on behalf of Mr.
Cerrone and from Chris Liacouras and Neil Romberg on
behalf of the respondent. Id.; see App. 5–28.
Dr. Rosenstreich is a licensed clinician and immunolo-
gist, with a focus on allergies. App. 5–6. He testified that
Mr. Cerrone’s UC was caused by the three vaccines that
Mr. Cerrone received on October 7, 2015. App. 5. Dr.
Rosenstreich based that opinion on the theory of molecular
mimicry, which is the theory that molecular similarities be-
tween different kinds of cells can cause the immune system
to react similarly to both despite one (a foreign agent) being
threatening and the other (the host’s own cells) being non-
threatening. App. 47. Dr. Rosenstreich explained that
there are similarities between the viral proteins in the vac-
cines and the proteins in Mr. Cerrone’s body relevant to
Case: 24-1281 Document: 39 Page: 3 Filed: 07/29/2025

-- 3 of 16 --

CERRONE v. HHS 4
UC, and that Mr. Cerrone’s immune system may have mis-
takenly attacked those proteins. App. 8. Although Dr.
Rosenstreich testified that any of the three vaccines could
have triggered the molecular mimicry in Mr. Cerrone’s
case, he focused on the HPV vaccine. Id.
As an alternative to his molecular mimicry theory, Dr.
Rosenstreich testified that the vaccines could have trig-
gered Mr. Cerrone’s UC through other less immunologi-
cally specific mechanisms, and he offered some examples of
such mechanisms. App. 9. Dr. Rosenstreich supported his
opinions by reference to various journal articles, the HPV
vaccine package insert, case reports, and reports from the
Vaccine Adverse Event Reporting System.1 App. 9–11.
Dr. Rosenstreich testified that his causation theory
was consistent with Mr. Cerrone’s medical history. He pos-
ited that Mr. Cerrone was likely susceptible to UC, either
genetically or as a result of environmental factors. App. 13.
According to Dr. Rosenstreich, Mr. Cerrone’s report of de-
creased stamina and stability was an early manifestation
of systemic inflammation. Id. Dr. Rosenstreich further
testified that the fact that Mr. Cerrone’s condition wors-
ened after his second HPV vaccine supported the theory
that an immune reaction caused Mr. Cerrone’s disease, be-
cause immune responses to a second vaccine exposure typ-
ically manifest more quickly and robustly than responses
to the first exposure. App. 14. Finally, Dr. Rosenstreich
explained that his causation theory was consistent with the
81-day delay between Mr. Cerrone’s vaccination and the
onset of blood in his stools because it takes time for the im-
mune response to cause such severe damage. App. 15. In
1 The Vaccine Adverse Event Reporting System is a
database maintained by the Centers for Disease Control
and Prevention that compiles information from the public
about reactions to immunizations. App. 11 n.28.
Case: 24-1281 Document: 39 Page: 4 Filed: 07/29/2025

-- 4 of 16 --

CERRONE v. HHS 5
Dr. Rosenstreich’s opinion, a delay of that length was con-
sistent with the pertinent medical literature. Id.
Dr. Santoro, Mr. Cerrone’s other expert, is a gastroin-
testinal physician. App. 16. He did not testify live but sub-
mitted a report and affidavit. Id. The special master found
his opinions to be largely duplicative of Dr. Rosenstreich’s
opinions. Id.
Dr. Liacouras, who testified for the respondent, is a pe-
diatric gastroenterologist. App. 17. He explained that UC
is considered an autoimmune disease that has a largely un-
known etiology, although genetic, environmental, autoim-
mune, and bacterial factors are all possible explanations.
App. 17. He did not dispute Mr. Cerrone’s UC diagnosis.
Based largely on the timing of Mr. Cerrone’s disease pro-
gression, however, he disagreed that Mr. Cerrone’s vac-
cinations were the likely cause of his disease. App. 18.
Dr. Liacouras focused on Mr. Cerrone’s disease pro-
gression as documented in his medical records, noting that
no gastrointestinal bleeding was recorded until February
13, 2016. App. 18. Dr. Liacouras discounted Mr. Cerrone’s
self-reported decreased stamina and stability, because
those symptoms have many possible causes unrelated to
UC. App. 19. Given the delay between the vaccinations
and the onset of Mr. Cerrone’s UC symptoms, Dr.
Liacouras concluded that it was unlikely that vaccines
caused Mr. Cerrone’s UC. Id. Dr. Liacouras also based his
opinion on a review of the relevant medical literature,
which he described as suggesting that vaccines are not
commonly associated with the development of UC. Id.
Dr. Romberg, the respondent’s other expert, is an im-
munologist. App. 20. In his testimony, he addressed Dr.
Rosenstreich’s theory of causation. App. 21. Regarding
molecular mimicry, Dr. Romberg explained that while the
general theory of molecular mimicry has a reasonable sci-
entific basis, it is unlikely to be the mechanism underlying
any given autoimmune disease unless there is specific
Case: 24-1281 Document: 39 Page: 5 Filed: 07/29/2025

-- 5 of 16 --

CERRONE v. HHS 6
evidence to suggest its involvement. App. 23. He identified
types of evidence that could suggest its involvement, none
of which he found to be present in Mr. Cerrone’s case. App.
23–24.
Following the evidentiary hearing, the special master
denied Mr. Cerrone’s claim for compensation. The special
master explained that Mr. Cerrone had failed to prove by a
preponderance of the evidence that his injuries were
caused by one of the vaccines he had received.
Mr. Cerrone appealed the special master’s decision to
the Court of Federal Claims, which affirmed that decision
in a detailed opinion. App. 44–59.
II
A
In Vaccine Act cases, the Court of Federal Claims re-
views the factual findings of the special master under the
arbitrary and capricious standard and reviews the legal
rulings of the special master to determine whether they are
in accordance with law. Moberly ex rel. Moberly v. Sec’y of
Health & Hum. Servs., 592 F.3d 1315, 1321 (Fed. Cir. 2010)
(citing Munn v. Sec’y of Health & Hum. Servs., 970 F.2d
863, 870 n.10 (Fed. Cir. 1992)). On appeal from decisions
of the Court of Federal Claims in such cases, we conduct de
novo review. As such, “this court performs the same task
as the Court of Federal Claims and determines anew
whether the special master’s findings were arbitrary or ca-
pricious.” Lampe v. Sec’y of Health & Hum. Servs., 219
F.3d 1357, 1360 (Fed. Cir. 2000). Therefore, “although we
are reviewing as a matter of law the decision of the [Court
of Federal Claims] under a non-deferential standard, we
are in effect reviewing the decision of the special master
under the deferential [arbitrary] and capricious standard
on factual issues,” and independently, that is, without
Case: 24-1281 Document: 39 Page: 6 Filed: 07/29/2025

-- 6 of 16 --

CERRONE v. HHS 7
deference on legal issues. Porter v. Sec’y of Health & Hum.
Servs., 663 F.3d 1242, 1249 (Fed. Cir. 2011).2
The Vaccine Act distinguishes between “Table injuries”
and “off-Table injuries.” When a designated condition fol-
lows the administration of a designated vaccine within a
designated period of time, the injury is referred to as a Ta-
ble injury, and causation is presumed. 42 U.S.C. §§ 300aa-
11(c), 300aa-14; see, e.g., Munn, 970 F.2d at 856–66;
Lampe, 219 F.3d at 1360; Moberly, 593 F.3d at 1321; Por-
ter, 663 F.3d at 1249. All other injuries alleged to be caused
by a vaccine are considered off-Table injuries. For those
injuries, causation must be proved in each case.
The Vaccine Act expressly states that in off-Table
cases, such as this one, the petitioner must prove causation
by a preponderance of the evidence. 42 U.S.C. § 300aa-
13(a)(1); Moberly, 592 F.3d at 1321; H.R. Rep. No. 908, 99th
Cong., 2d Sess., pt. 1, at 15 (1986) (in off-Table cases, the
petitioner “must affirmatively demonstrate that the injury
or aggravation was caused by the vaccine”).
B
In Althen v. Secretary of Health & Human Services, 418
F.3d 1274 (Fed. Cir. 2005), we explained that a petitioner
seeking compensation for an off-Table injury
is to show by preponderant evidence that the vac-
cination brought about [petitioner’s] injury by
providing: (1) a medical theory causally connecting
2 Although we do not defer to the decisions of the
Court of Federal Claims in Vaccine Act cases, we do not
ignore them. To the contrary, we pay close attention to the
views of the Court of Federal Claims in these cases and
benefit from that court’s careful analysis of the parties’ le-
gal and factual presentations when conducting our own in-
dependent review.
Case: 24-1281 Document: 39 Page: 7 Filed: 07/29/2025

-- 7 of 16 --

CERRONE v. HHS 8
the vaccination and the injury; (2) a logical se-
quence of cause and effect showing that the vac-
cination was the reason for the injury; and (3) a
showing of a proximate temporal relationship be-
tween vaccination and injury.
Id. at 1278.
The three requirements set forth in Althen are drawn
from the earlier decisions of this court in Grant v. Secretary
of Department of Health & Human Services, 956 F.2d 1144,
1148 (Fed. Cir. 1992), and Hines ex rel. Sevier v. Secretary
of Health & Human Services, 940 F.2d 1518, 1525 (Fed.
Cir. 1991). In Grant, we explained that
temporal association alone does not suffice to show
a causal link between the vaccination and the in-
jury. To prove causation in fact, petitioners must
show a medical theory causally connecting the vac-
cination and the injury. . . . Causation in fact re-
quires proof of a logical sequence of cause and effect
showing that the vaccination was the reason for the
injury. A reputable medical or scientific explana-
tion must support the logical sequence of cause and
effect.
956 F.2d at 1148; see also Hines, 940 F.2d at 1525. The
Althen formulation, read in conjunction with Grant, thus
requires not only temporal association between the vaccine
and the injury, but also a reputable medical explanation for
the relationship and a logical sequence of cause and effect.
Moreover, as this court has made clear, the petitioner must
prove “all three Althen prongs by a preponderance of the
evidence.” Boatmon v. Sec’y of Health & Hum. Servs., 941
F.3d 1351, 1355 (Fed. Cir. 2019); Oliver v. Sec’y of Health
& Hum. Servs., 900 F.3d 1357, 1361 (Fed. Cir. 2018).
Mr. Cerrone’s argument on appeal focuses on the first
factor in the Althen formulation; as to that factor, he argues
that he only needed to show that it was biologically
Case: 24-1281 Document: 39 Page: 8 Filed: 07/29/2025

-- 8 of 16 --

CERRONE v. HHS 9
plausible that the vaccine caused his injury. Br. 14. He
explains that his experts identified a specific biological
mechanism connecting his vaccination to his injury—mo-
lecular mimicry—and that they identified circumstantial
evidence to support that causal theory. Br. 20. Based on
that evidence, Mr. Cerrone concludes that he has satisfied
his burden under the first Althen factor of showing a repu-
table medical theory demonstrating a causal connection be-
tween the vaccines he received and his injury.
Mr. Cerrone’s argument understates the burden he
bears under the first factor in the Althen formulation. He
is correct that a Vaccine Act petitioner’s showing need not
rise to the level of scientific certainty, nor is the petitioner
required to provide “detailed medical and scientific exposi-
tion on the biological mechanisms.” Knudsen v. Sec’y of
Dept. of Health & Hum. Servs., 35 F.3d 543, 549 (Fed. Cir.
1994). But the petitioner must provide the basis for a find-
ing of causation by a preponderance of the evidence. See
Broekelschen v. Sec’y of Health & Hum. Servs., 618 F.3d
1339, 1345 (Fed. Cir. 2010); Moberly, 592 F.3d at 1325. As
such, we have repeatedly stated that “simply identifying a
‘plausible’ theory of causation is insufficient for a petitioner
to meet her burden of proof.” LaLonde v. Sec’y of Health &
Hum. Servs., 746 F.3d 1334, 1339 (Fed. Cir. 2014); see also
Boatmon, 941 F.3d at 1360 (same); W.C. v. Sec’y of Health
& Hum. Servs., 704 F.3d 1352, 1356 (Fed. Cir. 2013) (hold-
ing that a theory that is at best “plausible” does not satisfy
petitioner’s burden of proof); Moberly, 592 F.3d at 1325
(proof of actual causation “‘must be supported by a sound
and reliable medical or scientific explanation.’” (quoting
Knudsen, 35 F.3d at 548)).3
3 On a few occasions this court has used the term
“plausible” in referring to Althen’s requirement to show a
Case: 24-1281 Document: 39 Page: 9 Filed: 07/29/2025

-- 9 of 16 --

CERRONE v. HHS 10
The second Althen factor underscores the need for a
reputable—as opposed to merely plausible—medical the-
ory explaining how the vaccine caused the petitioner’s in-
jury. Specifically, the second factor requires the petitioner
to point to a logical sequence of cause and effect showing
that the vaccination was the reason for the injury. See, e.g.,
Capizzano v. Sec’y of Health & Hum. Servs., 440 F.3d 1317,
1327 (Fed. Cir. 2006) (“The proper inquiry is whether a pe-
titioner in an off-Table injury case establishes a logical se-
quence of cause and effect, the second prong of Althen [], by
a preponderance of the evidence.”). As such, it requires the
petitioner to prove, by a preponderance of the evidence,
that the medical theory was in fact the mechanism that re-
sulted in the injury at issue. See Broekelschen, 618 F.3d at
1345 (“Because causation is relative to the injury, a peti-
tioner must provide a reputable medical or scientific expla-
nation that pertains specifically to the petitioner’s
case . . . .”).
The third Althen factor—a proximate temporal rela-
tionship between the vaccination and the injury—serves as
a check on the first two factors. While this court’s cases
make clear that temporal association is not enough by itself
to prove causation, see Boatmon, 941 F.3d at 1354;
LaLonde, 746 F.3d at 1341; Grant, 956 F.2d at 1148, the
medical theory causally connecting the vaccination and the
injury. But in those cases, the court was merely noting that
the government had not disputed the medical plausibility
of the petitioner’s theory of causation. Paluck v. Sec’y of
Health & Hum. Servs., 786 F.3d 1375, 1380 (Fed. Cir.
2015); Andreu ex rel. Andreu v. Sec’y of Health & Hum.
Servs., 569 F.3d 1367, 1375 (Fed. Cir. 2009). As noted, the
court’s precedents have consistently held that the first Al-
then factor requires the petitioner to show a reliable medi-
cal theory of causation specific to the vaccine and injury in
question, not merely one that is plausible.
Case: 24-1281 Document: 39 Page: 10 Filed: 07/29/2025

-- 10 of 16 --

CERRONE v. HHS 11
absence of temporal association can be enough to defeat a
claim of causation, see Pafford v. Sec’y of Health & Hum.
Servs., 451 F.3d 1352, 1356, 1358 (Fed. Cir. 2006).
When applying Althen, the special master must con-
sider the degree to which each factor is satisfied. And then,
after weighing the degree to which the petitioner has
proved each factor and considering any remaining evidence
bearing on causation, the special master must determine
whether the petitioner has proved that it is more likely
than not that the vaccine caused his injury. See, e.g., An-
dreu, 569 F.3d at 1382 (holding that “the totality of the ev-
idence—including the striking temporal connection
between the vaccine and [petitioner’s] initial seizure, the
testimony of treating physicians, and the biologic and sci-
entific plausibility of [petitioner’s expert’s] theory of causa-
tion—[was] sufficient to meet the Vaccine Act’s
preponderant evidence standard”).
C
The special master found Mr. Cerrone’s proof wanting
as to all three Althen factors and concluded that Mr. Cer-
rone failed to prove causation by a preponderance of the
evidence.
1
As for the first Althen factor, on which Mr. Cerrone
principally focuses, the special master found that Mr. Cer-
rone failed to establish by a preponderance of the evidence
that “UC can be vaccine-caused—and if so, that the immu-
nologic processes would work as proposed to cause it (even
if UC is immune-mediated, as the experts generally
agreed).” App. 35–36.
Mr. Cerrone argues that the special master imposed an
impermissibly heightened burden when concluding that
Mr. Cerrone’s medical theory failed to provide a causal con-
nection between his injury and his vaccinations. We
Case: 24-1281 Document: 39 Page: 11 Filed: 07/29/2025

-- 11 of 16 --

CERRONE v. HHS 12
disagree. The special master correctly explained that “the
evidence a claimant offers must, in totality, always accom-
plish one thing in the end: preponderantly establish that
the vaccine(s) at issue more likely than not can cause the
relevant disease.” App. 35 (emphasis in original). The spe-
cial master added that the plausibility of a theory “does not
mean this burden has been carried, unless the overall
weight of evidence . . . balances out in a claimant’s favor.”
Id. (emphasis in original).
The special master then proceeded to weigh the rele-
vant evidence offered by Mr. Cerrone, including the testi-
mony from his experts, the testimony from the
respondent’s experts, and the medical literature offered by
each party. App. 35–39. Ultimately, the special master
concluded that the testimony offered by Dr. Rosenstreich
was less persuasive than the testimony offered by the re-
spondent’s experts. Based on that conclusion, the special
master determined that Mr. Cerrone’s evidence “does not
amount to a preponderant showing, even if individual
items of evidence offered in this case had their own specific
reliability or reputability—or even if the core idea that vac-
cines could cause UC has some degree of plausibility.” App.
39.
Mr. Cerrone challenges the special master’s reliance on
medical literature, arguing that there is no requirement
that Mr. Cerrone must “provide preponderant proof of vac-
cine causation in the medical literature.” Reply Br. 8. We
agree with Mr. Cerrone that he is not required to present
medical literature to support his causation theory. See An-
dreu, 569 F.3d at 1378–79. But we disagree that the spe-
cial master implicitly imposed such a requirement on Mr.
Cerrone. Rather, the special master noted that “Dr.
Rosenstreich had sufficient qualifications to offer an opin-
ion on the purported immunologic processes due to vaccina-
tion that theoretically could cause UC,” but he found that
Dr. Rosenstreich “relied on no specific research or experi-
ence of his own” to support his theory. App. 39. In
Case: 24-1281 Document: 39 Page: 12 Filed: 07/29/2025

-- 12 of 16 --

CERRONE v. HHS 13
reviewing the evidence, the special master found that the
respondent’s experts were “more credentialed, better able
to connect their testimony to their personal experience, and
proved significantly more persuasive in explaining” their
opinions. Id.
Moreover, with respect to the medical literature, the
special master noted that the respondent pointed to several
studies that found no relationship between vaccines and
UC, including one study that found no relationship be-
tween IBD and two of the three vaccines at issue in this
case. App. 36. While Mr. Cerrone takes issue with the fac-
tual findings underlying the special master’s decision with
respect to factor one of Althen, we do not find those findings
to be arbitrary or capricious.
2
With regard to the second Althen factor—whether the
evidence supported a logical sequence of cause and effect
showing that the vaccines were the reason for his injury—
Mr. Cerrone again contends that the special master im-
posed an impermissible legal burden on him by concluding
that “the record is ‘lacking’ in the type of direct evidentiary
proof that is necessary to prove causation.” Br. 49.
Nothing in the special master’s analysis of the facts
suggests that he was imposing an improper legal burden
on Mr. Cerrone to prove a causal connection between the
vaccines he received and his injury. Rather, the special
master appropriately considered the facts in evidence, in-
cluding Mr. Cerrone’s circumstantial evidence. Ulti-
mately, the special master determined that the evidence
failed to meet Mr. Cerrone’s burden given that (1) none of
Mr. Cerrone’s treating physicians proposed an association
between Mr. Cerrone’s vaccinations and his subsequent di-
agnosis, (2) there was no evidence of an initial vaccine re-
action that would reflect the start of an inflammatory
process, and (3) there was an absence of any corroboration
of the symptoms Mr. Cerrone reported experiencing in
Case: 24-1281 Document: 39 Page: 13 Filed: 07/29/2025

-- 13 of 16 --

CERRONE v. HHS 14
November 2015, which in any event were non-specific for
UC. App. 39–40.
The special master also found that Mr. Cerrone’s “re-
challenge” argument was unsupported by the record.
While the special master acknowledged that Mr. Cerrone’s
symptoms worsened shortly after his receipt of a second
HPV vaccine dose in February 2016, the special master
noted that the temporal gap between the first HPV vaccine
dose and any likely UC-related symptoms was inconsistent
with an “initial ‘challenge’ that could reasonably be meas-
ured against his medical history after the second dose.”
App. 40. Based on the evidence, the special master con-
cluded that it is “as likely that Petitioner was already pro-
gressing symptomatically, independent of the second dose”
prior to February 2016. Id. The special master added that
the third HPV dose did not result in any reaction that could
be viewed as a further rechallenge event. Id. Based on
those findings, which are supported by the record, we up-
hold the special master’s conclusion that Mr. Cerrone failed
to show a logical sequence of cause and effect connecting
the vaccines with his injury.
3
With respect to the third Althen factor—a showing of a
proximate temporal relationship between vaccination and
injury—Mr. Cerrone argues that the evidence shows that
the 81-day delay between the administration of the vaccine
and the development of his UC symptoms was not contrary
to his theory of causation. After reviewing Mr. Cerrone’s
evidence on the temporal relationship factor, the special
master concluded otherwise. App. 41.
As to the aspect of Mr. Cerrone’s theory focusing on an
innate response to the vaccines, the special master con-
cluded, based on Dr. Romberg’s testimony and the record
evidence, that there was “simply no medical record support
that would establish an aberrant, subacute immune re-
sponse that was occurring in November or most of
Case: 24-1281 Document: 39 Page: 14 Filed: 07/29/2025

-- 14 of 16 --

CERRONE v. HHS 15
December 2015, that would (a) later manifest 81 days after
vaccination, but (b) remain tolerable another four to six
weeks, before becoming severe enough to encourage Peti-
tioner to seek emergency treatment.” Id. As to Mr. Cer-
rone’s argument that he suffered symptoms of fatigue or
stamina loss in November 2015, the special master found
that those symptoms were uncorroborated and in any event
were not shown to be typical precursors to a UC diagnosis.
App. 42.
In response to Mr. Cerrone’s reliance on other evidence
bearing on the third Althen factor, the special master found
Mr. Cerrone’s showing to be “unsupported by sufficient re-
liable independent proof.” Id. The special master con-
cluded that the individual case reports cited by Mr.
Cerrone were “facially inconsistent with the timeframe at
issue, with one in particular involving an extremely short
onset period not at all compatible to what occurred herein.”
Id. Similarly, the special master found that animal models
specific to IBD and UC “suggested a very rapid response
time after insult—less than one week.” Id. Although the
special master did not make a finding as to what period of
time would support a finding that UC was vaccine-caused,
the special master concluded that the evidence “at least
shows that a lengthy timeframe has reliability issues that
Petitioner’s evidence did not fully address or refute.” App.
42–43.
With respect to the third Althen factor, we do not find
the special master’s conclusion that Mr. Cerrone failed to
show a proximate relationship between his vaccinations
and his injury by a preponderance of the evidence to be ar-
bitrary or capricious.
4
Finally, Mr. Cerrone challenges the special master’s
credibility determinations with regard to the testifying ex-
perts. Reply Br. 18. In addition to finding Dr.
Rosenstreich’s testimony less credible than Dr. Romberg’s
Case: 24-1281 Document: 39 Page: 15 Filed: 07/29/2025

-- 15 of 16 --

CERRONE v. HHS 16
on particular points, the special master found that alt-
hough Dr. Rosenstreich offered his theory in good faith,
“his opinion ultimately seemed more designed to serve the
needs of Petitioner in this case than to reflect an independ-
ent trustworthy view.” App. 39. By contrast, the special
master found the respondent’s testifying experts to be
“more credentialed, better able to connect their testimony
to their personal experience, and . . . significantly more
persuasive in explaining why the three vaccines Petitioner
received could not likely cause UC.” Id. The special master
further found their rejection of Mr. Cerrone’s theory “to be
derived less from a claim-oriented desire to assist their side
to prevail, but more to reflect their own independent and
honest assessment of the theories and facts at issue.” Id.
As we have held in this context and others, credibility
determinations are virtually unreviewable on appeal. See
Porter, 663 F.3d at 1249; Lampe, 219 F.3d at 1362; Bradley
v. Sec’y of Health & Hum. Servs., 991 F.2d 1570, 1575 (Fed.
Cir. 1993); Munn, 970 F.2d at 871 (“[O]f course we do not
examine the probative value of the evidence or the credibil-
ity of the witnesses. These are all matters within the pur-
view of the fact finder.”). The special master’s credibility
determinations thus buttress his findings on the Althen
factors, which cannot reasonably be found to be arbitrary
or capricious.
III
For the foregoing reasons, we uphold the special mas-
ter’s analysis and conclusions regarding the Althen factors
and thus the ultimate issue of causation. We therefore af-
firm the decision of the Court of Federal Claims.
AFFIRMED
COSTS
No costs.
Case: 24-1281 Document: 39 Page: 16 Filed: 07/29/2025

-- 16 of 16 --