Defenza v. Secretary of Health and Human Services

In the United States Court of Federal Claims STACY L. DEFENZA as administrator of ESTATE OF LINDA L. CHERVENOK, Petitioner, No. 18-1601 v. (Filed Under Seal: May 29, 2026) (Reissued Publicly: June 16, 2026) SECRETARY OF HEALTH AND HUMAN SERVICES, Respondent. Jeffrey S. Pop, Kristina E. Grigorian, Jeffrey S. Pop & Associates, Beverly Hills, California, for Petitioner. Nina Y. Ren, Trial Attorney, Julia M. Collison, Assistant Director, Heather L. Pearlman, Deputy Director, Jonathan D. Guynn, Acting Director, Torts Branch, Brett A. Shumate, Assistant Attorney General, Civil Division, United States Department of Justice, Washington, DC, for Respondent. OPINION AND ORDER1 HADJI, Judge. Petitioner seeks review of a decision denying her petition for compensation under the National Vaccine Injury Compensation Program. For the reasons stated below, Petitioner’s Motion for Review (ECF 109) is DENIED, and the Special Master’s Decision (ECF 107) is SUSTAINED. BACKGROUND I. Petitioner’s Medical History The underlying facts set forth in Petitioner’s medical records are few and undisputed. Accordingly, the Court adopts such facts as set forth in the Special Master’s Decision and briefly recounts them here. 1 This Opinion was issued under seal on May 29, 2026. The parties were directed to propose redactions by June 12, 2026. No proposed redactions were received. The Court hereby publicly releases the Opinion and Order in full.  On October 21, 2015, Petitioner Linda L. Chervenok received a flu vaccination.2 ECF 107 at 5. The next day, she began experiencing shortness of breath, numbness, tingling, and flaccid paralysis in her extremities. Id. Petitioner was ultimately diagnosed with Guillain-Barre Syndrome (GBS). Id. Petitioner’s October 2015 flu vaccination was not her first; she had previously received flu vaccinations, including some that contained H1N1 components. Id. at 6. Petitioner also suffered from chronic lower back pain. Id. On October 8, 2015, approximately two weeks prior to the vaccination at issue, Petitioner underwent a radiofrequency ablation procedure to treat this condition. Id. II. The Petition and Procedural History On October 16, 2018, Petitioner filed a petition for compensation under the National Vaccine Injury Compensation Program, 42 U.S.C. §300aa-10, et seq.,3 alleging that her October 2015 flu vaccine caused her to develop GBS. ECF 1 at 1. In support of her claim, Petitioner submitted medical records, affidavits, and an opinion letter from her treating neurosurgeon, Allison Rathmann, D.O. See ECF 9, 13, 37. Respondent submitted his Rule 4(c) Report, which primarily argued that the petition should be dismissed due to the 24- hour post-vaccination period of onset. See generally ECF 29. In response, Petitioner submitted an expert report by neuroimmunologist Lawrence Steinman, M.D., along with supporting medical literature. See generally ECF 34-1, 37. Dr. Steinman opined that the flu vaccine can cause GBS within 24 hours via molecular mimicry and that a recall antibody response due to prior flu vaccinations can manifest within 24 hours. ECF 34-1 at 1. Disputing causation, Respondent filed a responsive expert report and supporting medical literature by immunologist J. Lindsay Whitton, M.D., Ph.D. See generally ECF 43-1. Dr. Whitton characterized Dr. Steinman’s theories of molecular mimicry as “deeply flawed” and challenged his opinion that molecular mimicry can lead to disease within 24 hours, even in the context of a recall response. Id. at 26. Following review of Drs. Steinman and Whitton’s expert reports, the Special Master issued a Rule 5 Order expressing skepticism that Petitioner could meet her burden of proof under the three-prong test articulated in Althen v. Secretary of Health & Human Services, which requires petitioners, in relevant part, to establish a “proximate temporal relationship” between the vaccination and the injury alleged. 418 F.3d 1274, 1278 (Fed. Cir. 2005); see ECF 44 at 1. Recognizing that much of the reasoning in Dr. Steinman’s expert report regarding onset had been previously rejected by another special master, the Special Master 2 Petitioner Linda L. Chervenok passed away in April 2025. ECF 103-1. Her daughter, Stacy L. DeFenza, has been substituted for Petitioner as estate administrator. See ECF 109 at 6; see also Docket, Case No. 18- 1601. 3 The National Vaccine Injury Compensation Program was established by the National Childhood Vaccine Injury Act of 1986, Pub. L. No. 99-660, 100 Stat. 3755 (the Vaccine Act). 2 recommended that Petitioner strongly consider the voluntary dismissal of her claim. ECF 44 at 1-2 (citing Rowan v. Sec’y of Health & Hum. Servs., No. 17-760, 2020 WL 2954954 (Fed. Cl. Spec. Mstr. Apr. 28, 2020)). Rather than do so, Petitioner submitted a supplemental expert report from Dr. Steinman, focused on the timing of onset. See generally ECF 46-1. Respondent countered with a responsive supplemental report by Dr. Whitton. See generally ECF 51-1. Petitioner and Respondent each filed an additional supplemental expert report, through which they continued to offer divergent opinions on the significance of the short interval between Petitioner’s vaccination and the onset of GBS. See generally ECF 53-2; 55-1. Petitioner also filed a second opinion letter by her treating neurosurgeon. See generally ECF 53-1. The letter noted that “no other cause for [Petitioner’s] GBS was identified following a robust work up,” and described two pieces of medical literature that discussed the timing of onset of GBS following a flu vaccine, both of which Dr. Rathmann claimed supported a 1-2 day interval between flu vaccination and GBS. Id. at 1. Dr. Rathmann also reasserted her belief that the flu vaccination was more likely than not the cause of Petitioner’s GBS, though she “defer[red] to a neurologist or immunologist on how biologically this can occur.” Id. In the lead up to the entitlement hearing, the parties both filed additional evidence, including updated medical records and medical literature. See ECF 60, 61, 64, 66, 67, 68, 70, 71, 72. As relevant here, Petitioner ultimately introduced several epidemiological studies, which she contended provide support for the proposition that the flu vaccine can cause GBS within one day. These studies include the Schonberger,4 Salmon,5 Polakowski,6 and Park7 studies. See ECF 36-5 (Schonberger); ECF 47-2 (Salmon); ECF 68-4 (Polakowski); ECF 47-1 (Park). All four studies observed cases of GBS occurring within two days of vaccination. See ECF 107 at 19, 22-23. As described by the Special Master, the Schonberger study is a surveillance study conducted following a 1976 mass vaccination campaign. Id. at 19. It is generally accepted as providing support for the proposition that the flu vaccine can cause GBS and indicates that incidence of GBS was elevated relative to the first full week post-vaccination. Id. at 19-20. The Salmon and Polakowski studies were likewise conducted following a mass vaccination campaign, this time in 2009. Id. at 21. The Salmon study meta-analyzed an exposure window of 1-42 days and confirmed that first week results were statistically significant. Id. at 22. The Polakowski study, which examined chart-confirmed cases of GBS, similarly considered a risk period of 1-42 days. Id. It found an elevated risk of GBS for the six-week period following vaccination. Id. And 4 Lawrence B. Schonberger et al., Guillain-Barre Syndrome Following Vaccination in the National Influenza Immunization Program, United States, 1976-1977, 110 AM. J. EPIDEMIOLOGY 105 (1979). 5 Daniel A. Salmon et al., Association Between Guillain-Barre Syndrome and Influenza A (H1N1) 2009 Monovalent Inactivated Vaccines in the USA: A Meta-Analysis, 381 LANCER 1461 (2013). 6 Laura L. Polakowski et al., Chart-Confirmed Guillain-Barre Syndrome After 2009 H1N1 Influenza Vaccination Among the Medicare Population, 2009-2010, 178 AM. J. EPIDEMIOLOGY 962 (2013). 7 Yong-Shik Park et al., Clinical Features of Post-Vaccination Guillain-Barre Syndrome (GBS) in Korea, 32 J. KOREAN MED. SCI. 1154 (2017). 3 finally, the Park study examined the demographic characteristics of GBS patients who sought compensation from South Korea’s version of the Vaccine Program. Id. at 23. In that study, half of all examined cases developed symptoms within two days of vaccination. Id. On March 4-5, 2024, the Special Master held an entitlement hearing, where both experts testified. See ECF 92, 93. Following the hearing, both parties filed post-trial supplemental expert reports and post-hearing briefs. See generally ECF 95, 97-1, 98-1, 99, 100, 102. On January 7, 2026, the Special Master issued his Decision. ECF 107. The Special Master found that “there is no dispute that the onset of [Petitioner]’s GBS occurred about 24 hours post-vaccination,” and focused on what he characterized as the “core dispute” in this case: “whether that period of onset is appropriate for a causal inference based on Dr. Steinman’s theory of causation, which is based on molecular mimicry.” Id. at 9. The Special Master answered that question in the negative. Deeming the testimony of Respondent’s expert, Dr. Whitton, more persuasive than that of Petitioner’s expert, Dr. Steinman, the Special Master found that “Dr. Steinman has not come forward with a preponderantly supported explanation of how [P]etitioner’s flu vaccine could have produced an autoantibody response leading to a loss of immune self-tolerance and subsequent development of GBS within 24 hours of vaccination.” Id. at 18. Regarding the studies cited by Dr. Steinman, the Special Master determined that they “are not entirely lacking teachings potentially supportive of [P]etitioner’s view,” but “they do not ultimately add significantly to [P]etitioner’s claim,” given their respective weaknesses and limitations. Id. at 18-19. In particular, he found that the Schonberger, Salmon, and Polakowski studies did not include any calculations to support excess risk of GBS on Day 1, even though the studies technically expressed the period of elevated risk in a manner that did not exclude Day 1. See id. at 19-23. Crediting Dr. Whitton’s testimony that approximately five cases of GBS are expected each day purely as a result of chance, the Special Master further found that “one or two cases of GBS occurring on any given day could be the result of chance, greatly tempering the potential significance” of the Salmon and Polakowski studies, which each observed less than five cases on Day 1. Id. at 23. With respect to the Park study, the Special Master determined it was “difficult to draw any conclusions from this study” as it observed “a highly selective group” of people seeking compensation for perceived vaccine injury under South Korea’s vaccine injury compensation program and “we do not have information on what criteria the compensating authority uses to adjudge eligibility.” Id. at 23. More broadly, the Special Master found that “epidemiologic data is limited to demonstrating correlation, rather than causation,” and weighed Petitioner’s epidemiological studies accordingly. Id. at 20. Ultimately, the Special Master concluded that “the onset of [Petitioner]’s GBS occurred too soon after vaccination to be causally related.” Id. at 26 (emphasis omitted). On February 5, 2026, Petitioner timely filed a Motion for Review. ECF 109. Respondent filed his Memorandum in Response the following month. ECF 112. 4  STANDARD OF REVIEW Under the Vaccine Act, this Court has jurisdiction to review a special master’s entitlement decision. 42 U.S.C. § 300aa-12(e)(2). In reviewing a special master’s decision, this Court may: (A) uphold the findings of fact and conclusions of law of the special master and sustain the special master’s decision, (B) set aside any findings of fact or conclusion of law of the special master found to be arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law and issue its own findings of fact and conclusions of law, or (C) remand the petition to the special master for further action in accordance with the court’s direction. 42 U.S.C. § 300aa-12(e)(2)(A)-(C). The standards set forth in 42 U.S.C. § 300aa- 12(e)(2)(B) “vary in application as well as degree of deference” as “[e]ach standard applies to a different aspect of the judgment.” Munn v. Sec’y of Health & Hum. Servs., 970 F.2d 863, 870 n.10 (Fed. Cir. 1992). Findings of fact receive deferential review under the “arbitrary and capricious” standard; legal conclusions are reviewed de novo under the “not in accordance with law” standard; and discretionary rulings are reviewed for “abuse of discretion.” Turner v. Sec’y of Health & Hum. Servs., 268 F.3d 1334, 1337 (Fed. Cir. 2001). With respect to the arbitrary and capricious standard, “no uniform definition … has emerged,” but it is “a highly deferential standard of review” such that “[i]f the special master has considered the relevant evidence of record, drawn plausible inferences and articulated a rational basis for the decision, reversible error will be extremely difficult to demonstrate.” Hines v. Sec’y of Health & Hum. Servs., 940 F.2d 1518, 1527-28 (Fed. Cir. 1991); see also Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto Ins. Co., 463 U.S. 29, 43 (1983) (A decision is arbitrary and capricious only if it is “so implausible that it could not be ascribed to a difference in view….”). Accordingly, if a special master’s finding of fact is “based on evidence in the record that [is] not wholly implausible,” this Court is “compelled to uphold that finding as not being arbitrary or capricious.” Lampe v. Sec’y of Health & Hum. Servs., 219 F.3d 1357, 1363 (Fed. Cir. 2000). The “not in accordance with law” standard, on the other hand, is applied without deference to legal determinations, such as “[w]hether the special master applied the appropriate standard of causation . . . .” Deribeaux v. Sec’y of Health & Hum. Servs., 717 F.3d 1363, 1366 (Fed. Cir. 2013). Lastly, the abuse of discretion standard applies to the special master’s discretionary rulings, such as evidentiary determinations regarding the qualification of experts and the admissibility of their testimony. Piscopo v. Sec’y of Health & Hum. Servs., 66 Fed. Cl. 49, 53 (2005). Determinations subject to review for abuse of discretion must be sustained unless “manifestly erroneous.” Id.; see also Milmark Servs., Inc. v. United States, 731 F.2d 855, 860 (Fed. Cir. 1984). 5  DISCUSSION Under the Vaccine Act, petitioners bear the burden of proving, by a preponderance of the evidence, that a vaccine caused an injury or death. 42 U.S.C. § 300aa-13(a)(1); 42 U.S.C. § 300aa-11(c)(1)(C); Pafford v. Sec’y of Health & Hum. Servs., 451 F.3d 1352, 1355 (Fed. Cir. 2006). The Federal Circuit has “interpreted the ‘preponderance of the evidence’ standard referred to in the Vaccine Act as one of proof by a simple preponderance, of ‘more probable than not’ causation.” Althen, 418 F.3d at 1279. In considering the evidence, special masters are required to consider “the record as a whole.” 42 U.S.C. §300aa-13(a)(1). Because “the purpose of the Vaccine Act’s preponderance standard is to allow the finding of causation in a field bereft of complete and direct proof of how vaccines affect the human body,” Althen, 418 F.3d at 1280, proof of medical certainty is not required, Bunting v. Sec’y of Health & Hum. Servs., 931 F.2d 867, 873 (Fed. Cir. 1991). There are two methods by which a petitioner may establish causation and thus eligibility for compensation. Munn, 970 F.2d at 865. Through the first method, a petitioner may demonstrate causation through a statutorily prescribed presumption by showing that the alleged injury meets the criteria listed on the Vaccine Injury Table, as set forth in 42 U.S.C. § 300aa-14 and 42 C.F.R. § 100.3. Id. The Table identifies the covered vaccines, the corresponding injuries, and the time period after vaccination in which the particular injuries must occur. 42 C.F.R. § 100.3. “[I]f a petitioner can establish that [he] received a listed vaccine and experienced such symptoms or injuries within the specified timeframes, [he] has met [his] prima facie burden to prove that the vaccine caused [his] injuries.” de Bazan v. Sec’y of Health & Hum. Servs., 539 F.3d 1347, 1351 (Fed. Cir. 2008). Alternatively, petitioners who have suffered an “off-Table injury,” meaning their injury does not meet the criteria in the Table, must use the second method to prove causation. This method requires a petitioner to prove “causation-in-fact” by a preponderance of the evidence. See 42 U.S.C. § 300aa-11(c)(1)(C)(ii)(II), 42 U.S.C. § 300aa-13(a)(1); see also Broekelschen v. Sec’y of Health & Hum. Servs., 618 F.3d 1339, 1341-42 (Fed. Cir. 2010). “Once causation is established, the petitioner is entitled to compensation unless the Government can show by a preponderance of the evidence that the injury is due to factors unrelated to the vaccine, i.e., an alternative cause.” Porter v. Sec’y of Health & Hum. Servs., 663 F.3d 1242, 1249 (Fed. Cir. 2011). In the present case, Petitioner alleged that a flu vaccination caused her to suffer GBS. ECF 1 at 1. Although the Vaccine Injury Table lists GBS as a presumptive vaccine injury following the flu vaccine, onset of symptoms must occur “not less than 3 days and not more than 42 days” following vaccination for it to be considered a Table injury. See 42 C.F.R. § 100.3(a). Because Petitioner’s onset of symptoms did not begin within the timeframe listed on the Table, Petitioner concedes that she is not entitled to a presumption of causation and that she must thus establish causation-in-fact. ECF 109 at 9. Under the three-prong test articulated by the Federal Circuit in Althen, proving causation-in-fact requires a showing of: (1) a medical theory causally connecting the 6 vaccination and the injury; (2) a logical sequence of cause and effect showing that the vaccination was the reason for the injury; and (3) a proximate temporal relationship between vaccination and injury. 418 F.3d at 1278. Although a petitioner need not show that her vaccination was the sole cause of her injury, she must demonstrate that “the vaccine was not only a but-for cause of the injury but also a substantial factor in bringing about the injury.” Shyface v. Sec’y of Health & Hum. Servs., 165 F.3d 1344, 1352 (Fed. Cir. 1999). “[C]lose calls regarding causation are resolved in favor of injured claimants.” Althen, 418 F.3d at 1280. In the instant case, the Special Master found that Petitioner did not meet her burden in establishing causation-in-fact. See ECF 107 at 26. Petitioner contends the Special Master erred in four main ways. Specifically, she claims that he: (1) conflated requirements for Althen prong 1 in his assessment of Althen prong 3; (2) failed to consider the treating neurosurgeon’s opinion as evidence in his Althen prong 3 analysis; (3) failed to consider Petitioner’s elimination of alternative causes in assessing whether she satisfied her burden; and (4) used an elevated standard of proof when assessing epidemiological evidence. See ECF 109 at 6-7. The Court addresses each contention in turn. I. Alleged Conflation of Althen Prongs 1 and 3 Petitioner contends that the Special Master elevated her burden of proof by conducting an in-depth analysis of Petitioner’s medical theory of causation under his prong 3 analysis, thus conflating the requirements for Althen prongs 1 and 3. Id. at 22-24. She maintains that the Special Master “erroneously created his own 2-part test” and effectively required her “to demonstrate a precise biological mechanism of how GBS can occur in 1 day post vaccination.” Id. at 22, 24. Specifically, Petitioner takes issue with the following statement by the Special Master: Discussion of [prong 3] can be broken down into two distinct topics: First, whether Dr. Steinman has provided an immunologic explanation as to how an injury due to molecular mimicry can occur within 24 hours; and second, whether available epidemiology bolsters Dr. Steinman’s view or otherwise persuasively establishes an increased risk of post- vaccination GBS inclusive of the first day post-vaccination. ECF 107 at 9; see ECF 109 at 22 (citing same). The Court discerns no error in the Special Master’s analysis. First, the Court does not read the Special Master’s decision to create an improper two-part test or require Petitioner to demonstrate the precise biological mechanism by which a flu vaccine can cause GBS in one day, as alleged by Petitioner. ECF 109 at 22. By indicating that discussion of prong 3 would proceed in two parts, the Special Master merely signposted the discussion and previewed the nature of the prong 3 evidence before him. At no point did the Special Master state that, to succeed on prong 3, Petitioner was required to both: (1) provide an immunologic explanation as to how an injury due to molecular mimicry can 7 occur within 24 hours; and (2) provide epidemiological proof. Indeed, the Special Master’s language suggests the opposite. By acknowledging that epidemiological evidence might either “bolster[] Dr. Steinman’s view or otherwise persuasively establish[] an increased risk” on Day 1, the Special Master indicated that there was no requirement for Dr. Steinman to provide an immunologic explanation and that epidemiological evidence might be used to support prong 3 in lieu of Dr. Steinman’s expert opinion. See ECF 107 at 9 (emphasis added). At no point did the Special Master rule out the use of other evidence or fault Petitioner for failing to provide proof of specific biological mechanisms. Second, the Special Master properly recognized that, to satisfy prong 3, “[a] petitioner must offer ‘preponderant proof that the onset of symptoms occurred within a timeframe which, given the medical understanding of the disorder’s etiology, it is medically acceptable to infer causation-in-fact.’” Id. at 8 (quoting de Bazan, 539 F.3d at 1352 (emphasis added)). “As de Bazan indicates, the ‘etiology’ of the disorder determines the appropriate temporal relationship.” Veryzer v. Sec’y of Health & Hum. Servs., 100 Fed. Cl. 344, 356 (2011), aff’d per curiam, 475 App’x 765 (Fed. Cir. 2012). Accordingly, the Special Master correctly noted that “[t]he explanation for what is a medically acceptable timeframe must coincide with the theory of how the relevant vaccine can cause an injury (Althen prong one’s requirement).” ECF 107 at 8 (citing de Bazan, 539 F.3d at 1352). The Special Master then went on to evaluate whether Petitioner’s one-day onset of symptoms was compatible with Dr. Steinman’s theory of molecular mimicry. See id. at 9-18. In conducting this portion of the prong 3 analysis, the Special Master thoroughly evaluated whether Dr. Steinman persuasively explained how an injury due to molecular mimicry can occur within 24 hours. See id. He weighed Dr. Steinman’s assessment of the appropriate timing against Dr. Whitton’s competing views and concluded that “Dr. Steinman is not persuasive in contending … that the immune response underlying his theory can develop as quickly as he opines.” Id. at 10. Specifically, he found that “although Dr. Steinman has demonstrated that a secondary or recall response does develop more quickly than a primary immune response, the concept of a recall response does not explain how molecular mimicry can occur within 24 hours.” ECF 107 at 12. After considering concurrent immune processes proposed by Dr. Steinman, the Special Master further found that “Dr. Steinman has not come forward with a preponderantly supported explanation of how petitioner’s flu vaccine could have produced an autoantibody response leading to a loss of immune self-tolerance and subsequent development of GBS within 24 hours of vaccination.” Id. at 18. Ultimately, “[a]fter weighing the competing expert opinions,” the Special Master found that “[R]espondent is persuasive in contending that it is biologically implausible for GBS to develop in such a short period of time.” ECF 107 at 26. Thus, the Special Master properly evaluated whether the temporal association Petitioner proposed under the third Althen prong “relate[d] to the pathology of the specific medical theory alleged to have caused the injury.” Veryzer, 100 Fed. Cl. at 356. He did not commit an error of law. 8  II. The Treating Neurosurgeon’s Medical Opinion Although Petitioner concedes that the Special Master considered the treating physician’s opinion when discussing Althen prong 2, she argues that the Special Master committed legal error by failing to also consider such evidence as part of his Althen prong 3 analysis. ECF 109 at 19-22. This argument fails. To be sure, in Capizzano v. Secretary of Health & Human Services, the Federal Circuit held that a special master committed legal error by failing to consider the opinions of treating physicians. 440 F.3d 1317, 1326 (Fed. Cir. 2006). Specifically, having found that the first and third prongs of the Althen test were satisfied, the Federal Circuit held that, “[a]s far as the second prong is concerned, in our view, the chief special master erred in not considering the opinions of the treating physicians who concluded that the vaccine was the cause of [petitioner]’s injury.” Id. The Federal Circuit further explained: The fact that these physicians’ diagnoses may have relied in part on the temporal proximity of Ms. Capizzano’s injuries to the administration of the vaccine is not disqualifying. We see no reason why evidence used to satisfy one of the Althen III prongs cannot overlap to satisfy another prong. In other words, if close temporal proximity, combined with the finding that hepatitis B vaccine can cause RA, demonstrates that it is logical to conclude that the vaccine was the cause of the RA (the effect), then medical opinions to this effect are quite probative. Moreover, Althen III explained that medical records and medical opinion testimony are favored in vaccine cases, as treating physicians are likely to be in the best position to determine whether a logical sequence of cause and effect show[s] that the vaccination was the reason for the injury. Id. (internal citations and quotation marks omitted) (alteration in original). Although Capizzano discusses the probative value of treating physicians’ opinions specifically in the context of an Althen prong 2 analysis, several judges on this Court have extended Capizzano’s logic regarding the heightened relevance of such evidence to Althen prong 3. See, e.g., Campbell v. Sec’y of Health & Hum. Servs., 90 Fed. Cl. 369, 386-87 (2009) (Lettow, J.) (noting that statements made by treating physicians should be afforded more than “some consideration” in addressing Althen prong 3); Contreras v. Sec’y of Health & Hum. Servs., 107 Fed. Cl. 280, 299 (2012) (Bush, J.) (requiring that treating physician opinions be given “significant weight” and observing that “it is difficult to conceive of a treating physician who would conclude that a vaccine caused the petitioner’s illness without also concluding that the onset of the illness was within a medically- acceptable time frame”); Mosley v. Sec’y of Health & Hum. Servs., 119 Fed. Cl. 734, 742- 44 (2015) (Kaplan, J.) (finding that “the special master’s failure to even discuss [treating physicians’] opinions in her analysis of prong three constituted legal error”). 9  The undersigned need not decide whether to follow Campbell, Contreras, and Mosley in the present case because: (1) this case is distinguishable; and (2) any error in this regard was harmless. First, unlike in the aforementioned cases, the treating physician’s causal opinion included a caveat that calls into question whether she actually offered an opinion relevant to Althen prong 3. Specifically, Dr. Rathmann wrote, “I believe that my letter was correct and that the flu vaccination is more likely than not the cause of Ms. Chevenok’s [sic] GBS; however, I would defer to a neurologist or immunologist on how biologically this can occur.” ECF 53-1. As discussed, prong 3 “requires preponderant proof that the onset of symptoms occurred within a timeframe for which, given the medical understanding of the disorder’s etiology, it is medically acceptable to infer causation-in-fact.” de Bazan, 539 F.3d at 1352 (emphasis added). Because Dr. Rathmann defers to others on “how biologically this can occur,” the Court fails to see how she offered any real opinion as to whether Petitioner’s GBS began in a “medically acceptable” timeframe under the medical theory alleged to have caused Petitioner’s injury. See Veryzer, 100 Fed. Cl. at 356 (noting that “the temporal association must relate to the pathology of the specific medical theory alleged to have caused the injury”). The Court cannot fault the Special Master for failing to afford significant weight to the treating physician’s medical opinion in his prong 3 analysis when that opinion does not appear to speak to the relevant prong 3 question—whether the onset of Petitioner’s GBS began in a timeframe consistent with the medical understanding of her GBS’s etiology. de Bazan, 539 F.3d at 1352; see also Cedillo v. Sec’y of Health & Hum. Servs., 617 F.3d 1328, 1348 (2010) (finding no error in special master’s failure to assign significant probative weight where “none of the treating physicians concluded” that the vaccine caused a petitioner’s injury). Second, even if the Special Master had a duty to explicitly consider Dr. Rathmann’s medical opinion in his evaluation of Althen prong 3, any failure to do so was harmless error. See Hines, 940 F.2d 1526 (finding special master’s consideration of potentially improper evidence was harmless error where “the special master’s decision was based on a number of factors” and petitioner had not shown that reliance on the error “was likely critical to the result”). This Court has previously found harmless error in some circumstances where a special master may have impermissibly heightened a petitioner’s burden of proof. See, e.g., Caves v. Sec’y of Health & Hum. Servs., 100 Fed. Cl. 119, 145 (2011) (concluding that, to the extent the special master heightened petitioner’s burden of proof on Althen prong 1, any resulting errors were harmless as petitioner failed to meet her burden of proof on prong 2); Tebcherani ex rel. Tebcherani v. Sec’y of Health & Hum. Servs., 55 Fed. Cl. 460, 476 (2003) (holding that the Court was “constrained to find … errors to be harmless in this case, because neither the Special Master’s inappropriate reference of an alleged viral illness nor the improper assignment of the burden of proof impacted the ultimate decision”). Such is the case here. Petitioner concedes that the Special Master explicitly addressed Dr. Rathmann’s medical opinion in his analysis of Althen prong 2, demonstrating 10 that he considered it as part of his overall causation-in-fact analysis. ECF 107 at 7-8. Further, as noted above, Dr. Rathmann’s opinion was limited in that she expressly deferred to others on etiology, which minimized the value of her opinion to the extent it supported an appropriate temporal relationship under the medical theory alleged to have caused Petitioner’s injury. And finally, to support her opinion that “the onset of GBS may occur within 2 days post vaccination,” Dr. Rathmann relied on two medical studies that the Special Master discussed at length in his analysis of prong 3. See ECF 53-1 at 1 (citing the Salmon and Parks studies). In his description of Dr. Rathmann’s medical opinions, the Special Master noted that Dr. Rathmann cited the Salmon and Park epidemiological studies and explained that these studies were discussed in greater detail by the experts. ECF 107 at 6. He then went on to discuss those experts’ views. Id. at 21-23. As such, nothing in Dr. Rathmann’s letters provided any additional reasoning for the Special Master to address. Because Petitioner has not shown that the Special Master’s failure to explicitly consider Dr. Rathmann’s testimony under prong 3 “was likely critical to the result,” Hines, 940 F.2d at 1526, or “impacted the ultimate decision,” Tebcherani, 55 Fed. Cl. at 476, the Court deems any such potential error harmless. Therefore, Petitioner’s argument fails. III. Petitioner’s Elimination of Alternative Causes Next, Petitioner alleges the Special Master’s assessment of Petitioner’s prima facie case failed to consider evidence that Petitioner eliminated alternative infectious causes. ECF 109 at 24-25. This challenge lacks merit. Though a petitioner is not required to eliminate alternative causes to establish a prima facie case, she “is certainly permitted to use evidence eliminating other potential causes to help carry the burden on causation and may find it necessary to do so when the other evidence on causation is insufficient to make out a prima facie case.” Walther v. Sec’y of Health & Hum. Servs., 485 F.3d 1146, 1151 (Fed. Cir. 2007). “In such instances, clearly the special master must evaluate what evidence a claimant presents as part of determining whether the claimant makes a prima facie case.” Id. That said, “[a]lthough probative, neither a mere showing of a proximate temporal relationship between vaccination and injury, nor a simplistic elimination of other potential causes of the injury suffices, without more, to meet the burden of showing actual causation.” Althen, 418 F.3d at 1278. Here, the Special Master expressly acknowledged that “[n]o other cause of [Petitioner]’s GBS has been asserted.” ECF 107 at 5. He also noted that “the elimination of alternative causes” played a role in Dr. Rathmann’s causal opinion. Id. at 7-8. The Special Master then concluded that, under Althen, “these considerations standing alone do not carry petitioner’s burden of proof.” Id. at 8. The Special Master’s language makes clear that he did consider evidence that Petitioner ruled out possible alternative causes; he just did not give it the controlling weight Petitioner wishes he did. See ECF 109 at 24 (arguing the Special Master “did not consider the weight of absence of alternative causes”) (emphasis added). In this regard, Petitioner appears to invite this Court to second guess the 11 Special Master’s evaluation of the evidence, which this Court cannot do. See Porter, 663 F.3d at 1249. IV. Alleged Elevation of Petitioner’s Burden of Proof Petitioner argues that, when assessing the epidemiological evidence, the Special Master utilized an elevated standard of proof, effectively requiring her to prove her case with scientific certainty rather than preponderant evidence. ECF 109 at 10-19. Under this umbrella, she alleges four specific errors on the part of the Special Master. For the reasons that follow, the Court concludes that the Special Master’s disagreement with Petitioner’s interpretation of epidemiology does not mean he elevated her burden to scientific certainty. A. Epidemiological Evidence Requirement First, Petitioner maintains that the Special Master applied a higher evidentiary standard than Althen permits, requiring her to provide epidemiological evidence explicitly demonstrating statistically significant results for Day 1 in particular. See ECF 109 at 15, 16, 19. She argues that her epidemiological studies presented statistically significant findings for a risk period of 1-42 days, and the Special Master’s failure to credit those studies impermissibly elevated her burden of proof. See ECF 109 at 10-19. It is well settled that a petitioner need not present evidence of epidemiologic studies to prove their prima facie case. Capizzano, 440 F.3d at 1325. That does not mean, however, that special masters may not assess the reliability or probative value of any evidence a petitioner chooses to present. See Moberly ex rel. Moberly v. Sec’y of Health & Hum. Servs., 592 F.3d at 1325 (“But to say that proof in the form of epidemiological studies or well-established medical experience is not mandatory does not mean that the special masters in Vaccine Act cases are precluded from inquiring into the reliability of testimony….”); see also Knudsen by Knudsen v. Sec’y of Health & Hum. Servs., 35 F.3d 543, 548 (Fed. Cir. 1994) (holding proof of actual causation “must be supported by a sound and reliable medical or scientific explanation”). Indeed, special masters are entitled to “demand[] some degree of acceptable scientific support.” Hodges v. Sec’y of Health & Hum. Servs., 9 F.3d 958, 962 (Fed. Cir. 1993). Accordingly, “[a] special master may … properly consider the weakness of medical literature support when evaluating the overall reliability of scientific evidence.” Gamboa-Avila v. Sec’y of Health & Hum. Servs., 166 F. 4th 1318, 1322 (Fed. Cir. 2026) (citing Moberly, 592 F.3d at 1324). That is exactly what the Special Master did here. He started by expressly articulating and applying the preponderant evidence standard to the third Althen prong. See ECF 107 at 8, 18 (explaining a petitioner must offer preponderant proof of medically-acceptable onset and that Dr. Steinman had not come forward with a preponderantly supported explanation). Then, he explicitly wrote that he was not requiring epidemiological evidence. Id. at 18 (“Of course, the Federal Circuit has previously stressed that a petitioner is not obligated to prove a case with epidemiology.”). He went on to assess the reliability and persuasiveness of both Dr. Steinman’s theories and the epidemiological evidence proffered by Petitioner. 12  To be sure, the Special Master relied on the fact that none of the evidence submitted by Petitioner established that Day 1, in particular, included any excess risk of GBS. See, e.g., id. at 22. However, he also engaged in a robust analysis to determine whether the evidence Petitioner presented had “some indicia of reliability.” Moberly, 592 F.3d at 1324. With respect to Dr. Steinman’s theories, he weighed them against Dr. Whitton’s competing opinions and noted specific deficiencies that rendered Dr. Steinman’s view unpersuasive in his view. For example, the Special Master found that “although Dr. Steinman has demonstrated that a secondary or recall response does develop more quickly than a primary immune response, the concept of a recall response does not explain how molecular mimicr