Undue Hardship After Groff: Upholding Healthcare COVID-19 Vaccine Mandates and Excluding Unreliable Rebuttal Experts Under Rule 702

1. Introduction

In Sara Slattery v. Main Line Health Inc (3d Cir. Aug. 17, 2026) (nonprecedential), Dr. Sara Slattery—Medical Director at the Dee Adams Center for Integrative and Regenerative Practice—sued Main Line Health (MLH) under Title VII and the Pennsylvania Human Relations Act (PHRA), alleging religious discrimination after MLH denied her request for a religious exemption from its mandatory COVID-19 vaccination policy.

The central appellate issue became whether MLH established the “undue hardship” defense under Title VII (as clarified by the Supreme Court in Groff)—and, relatedly, whether the District Court properly excluded Slattery’s proposed rebuttal experts under Federal Rule of Evidence 702.

2. Summary of the Opinion

The Third Circuit affirmed summary judgment for MLH. The panel assumed without deciding that Slattery could establish a prima facie case of religious discrimination, and instead affirmed because MLH showed that granting Slattery’s requested accommodation would impose an undue hardship.

The court also upheld the District Court’s exclusion of Slattery’s rebuttal expert reports (Dr. Peter McCullough and Dr. Akram Boutros) under Rule 702, leaving Slattery without evidence sufficient to create a triable dispute on undue hardship.

3. Analysis

A. Precedents Cited

  • Groff v. DeJoy, 600 U.S. 447 (2023): The controlling standard. The panel applied Groff’s requirement that the employer show the accommodation would cause “substantial increased costs in relation to the conduct of its particular business” and that undue-hardship analysis is contextual, considering “the nature, size and operating cost” of the employer. This framed the court’s acceptance of MLH’s evidence about COVID-19 transmission risks in healthcare and operational burdens.
  • Atkinson v. Lafayette Coll., 460 F.3d 447 (3d Cir. 2006): Used to confirm that the PHRA is “interpreted coextensively with Title VII,” so the Title VII analysis resolved both federal and state claims.
  • United States ex rel. Spay v. CVS Caremark Corp., 875 F.3d 746 (3d Cir. 2017): Cited for the appellate principle that the court may affirm summary judgment “on any basis supported by the record,” enabling the panel to rest affirmance on undue hardship alone.
  • El v. Se. Pa. Transp. Auth., 479 F.3d 232 (3d Cir. 2007): Provided the summary-judgment evidentiary requirement that the nonmovant must point to “actual evidence in the record” from which a jury could find in her favor; bare assertions about other exemptions were insufficient.
  • Oddi v. Ford Motor Co., 234 F.3d 136 (3d Cir. 2000): Supplied the appellate standards of review for Rule 702 rulings (plenary review of interpretation; abuse-of-discretion review of admit/exclude decisions), shaping the deferential posture toward the District Court’s exclusions.
  • Schneider ex rel. Estate of Schneider v. Fried, 320 F.3d 396 (3d Cir. 2003): Quoted for the Rule 702 “trilogy”— qualification, reliability, and fit—and for the broader point that courts cannot accept expert conclusions without indicia of reliability.
  • Childers v. Joseph, 842 F.2d 689 (3d Cir. 1988): Cited for plenary review of summary judgment.

B. Legal Reasoning

1) The court’s “assume-and-decide” posture

Rather than resolve whether Slattery established a prima facie case, the panel assumed it arguendo and proceeded directly to undue hardship. This approach effectively treated undue hardship as dispositive and highlights that, post-Groff, an employer can win at summary judgment by building a concrete, context-specific record of substantial burdens.

2) Applying Groff to a healthcare vaccination policy

The panel emphasized undisputed facts: COVID-19’s global spread, its potentially fatal impact on vulnerable populations, MLH’s integrated healthcare system (hospitals, home healthcare, physician practices), and the role of patient-caregiver contact in transmission.

MLH’s expert (Dr. Daniel Salmon) supported the premise that healthcare personnel faced heightened risk of contracting and transmitting COVID-19, that unvaccinated persons were at increased risk of transmission/contracting in 2021, and that layered mitigation strategies (including vaccination) were more effective than PPE/testing alone. The court also credited job-specific facts: Slattery contracted for “direct patient care,” had not been using telehealth, and telehealth was difficult for MLH to administer.

Putting these facts into Groff’s framework, the panel concluded MLH showed that exempting an unvaccinated primary care physician in an in-person, patient-facing role would impose a burden “substantial in the overall context” of MLH’s business.

3) Failure of rebuttal evidence and the “other exemptions” argument

Slattery attempted to defeat undue hardship by asserting that MLH had granted religious exemptions to others. The panel rejected this because she offered only a bare assertion (one named doctor and “several” unnamed employees) without evidence identifying the accommodations, the comparators’ roles, or the operational conditions—insufficient under El v. Se. Pa. Transp. Auth. to create a genuine dispute.

4) Rule 702 expert exclusions as case-dispositive

The panel upheld exclusion of both rebuttal experts, which mattered because those reports were Slattery’s main vehicle for challenging MLH’s undue-hardship showing on transmission risk and mitigation efficacy.

  • Dr. Peter McCullough: The court agreed he was unqualified and unreliable for the specific rebuttal task. Despite experience in internal medicine and cardiology, he lacked practice in epidemiology, immunology, or infectious diseases before COVID-19—an especially salient deficiency given the “relative novelty” of the virus. The report also contained unsupported assertions and relied on a study while failing to address the study’s own limitations (including limits on vaccine effectiveness conclusions and potential detection bias for asymptomatic breakthrough infections).
  • Dr. Akram Boutros: The court agreed the report was unreliable because it cited only case-internal materials (exemption request, Dr. Salmon’s report, disclosures, EEOC manual, CMS rules) and did not provide external scientific sources or a discernible methodology. The panel reiterated that professional judgment alone, without reliability markers, cannot satisfy Rule 702.

C. Impact

Although designated “not precedential,” the opinion signals how the Third Circuit may operationalize Groff in healthcare settings: an employer can establish undue hardship with a detailed record tying the accommodation to patient-safety risk, workforce health, and operational constraints, especially for patient-facing clinicians.

The decision also illustrates a practical litigation lesson: in vaccine-mandate religious-accommodation cases, the Rule 702 gatekeeping ruling can determine whether a plaintiff can generate a factual dispute on undue hardship. Unsupported comparator claims (“others got exemptions”) and methodology-free expert opinions are unlikely to survive summary judgment.

4. Complex Concepts Simplified

  • Prima facie case (Title VII religious accommodation): The initial showing that the employee has a sincere religious belief conflicting with a job requirement, informed the employer, and suffered an adverse employment action for noncompliance.
  • Reasonable accommodation: A change to workplace rules or practices that allows an employee to follow a religious belief (e.g., reassignment, masking/testing, modified duties), so long as it remains workable for the employer.
  • Undue hardship after Groff: Not mere inconvenience. The employer must show the accommodation would cause substantial increased costs or burdens in the context of its business. In healthcare, that context includes patient safety, infection-control demands, staffing realities, and operational feasibility.
  • Summary judgment: A case is decided without trial when no genuine dispute of material fact exists and the movant is entitled to judgment as a matter of law. The nonmoving party must point to real evidence, not speculation or conclusory statements.
  • Rule 702 (“qualification, reliability and fit”): Experts must (1) be qualified in the relevant field, (2) use reliable methods and reasoning, and (3) offer opinions that actually help decide an issue in the case. Courts can exclude expert reports that lack a scientific basis, ignore limitations, or provide conclusions without method.

5. Conclusion

Sara Slattery v. Main Line Health Inc applies Groff v. DeJoy to uphold a healthcare employer’s denial of a religious exemption to a COVID-19 vaccination mandate where the employer substantiated a context-specific, substantial-burden showing and the employee failed to marshal admissible rebuttal evidence. The opinion also underscores that Rule 702 reliability and methodological rigor can be decisive in Title VII accommodation disputes that turn on medical and public-health evidence.