FILE PHOTO: A vial and syringe are seen in front of Merck logo in this illustration taken March 26, 2025. REUTERS/Dado Ruvic/Illustration/File Photo

By Mike Scarcella

WASHINGTON (Reuters) -The U.S. Supreme Court declined on Monday to hear a bid by a group of physicians and healthcare providers to revive their antitrust lawsuit accusing drugmaker Merck of misleading federal regulators to maintain a decades-long monopoly over the mumps vaccine market.

The justices turned away an appeal by the plaintiffs of a lower court's decision to throw out the lawsuit on the basis that the drugmaker was protected under a legal doctrine that immunizes companies from antitrust claims based on actions aimed at swaying government decision-making.

A collection of family doctors and physicians' groups from New Jersey and New York filed the lawsuit in 2012 in federal court in Philadelphia, seeking monetary damages.

Merck in a statement on Monday said the "lawsuit lacked any legal or factual basis, and Merck is pleased that the Supreme Court has sided with the lower courts and brought an end to it."

A lead attorney for the plaintiffs did not immediately respond to a request for comment.

The claims that had remained in the long-running litigation involved allegations that the plaintiffs were overcharged for New Jersey-based Merck's mumps vaccines as a result of the company's monopolization of the mumps vaccine market in violation of federal antitrust law and New Jersey and New York state laws.

The plaintiffs said that submissions by Merck to the U.S. Food and Drug Administration contained misrepresentations that effectively boxed out competitors such as GlaxoSmithKline and delayed market entry of a rival vaccine for more than a decade.

Merck made the only mumps vaccine in the United States from 1967 until 2022. It is sold as part of a combined vaccine against mumps, measles and rubella, known as MMR-II.

The FDA in the 1990s raised concerns that the mumps vaccine lost potency toward the end of its 24-month shelf life, according to the lawsuit. The lawsuit accused Merck of misleading the FDA in the 2000s about the potency and efficacy of the mumps vaccine. Merck boosted the vaccine's initial potency and submitted a supplemental application to the FDA to continue selling it without revising its efficacy claims.

The so-called Noerr-Pennington doctrine at issue in the case was established under a pair of Supreme Court decisions in the 1960s.

Merck has denied any wrongdoing and has argued that its communications with the FDA were legitimate regulatory submissions protected by Noerr-Pennington immunity.

The Philadelphia-based 3rd U.S. Circuit Court of Appeals found that Noerr-Pennington immunity is broad, though not absolute. Actions intended to influence government decision-making are not immune from liability if they are deemed a "sham," it said. But it decided that even if Merck's petitions to the FDA contained falsehoods, they were not "sham" petitions because they succeeded in obtaining the agency's approval.

In their request to the Supreme Court to hear their appeal, the plaintiffs had urged the justices to resolve what they said was a split among federal appeals courts over whether alleged intentional deception can fall outside Noerr-Pennington's protections.

Merck countered that the alleged misrepresentations did not materially affect any statement on the vaccine label. The company also said the FDA had taken no action to revise the label despite being made aware of the allegations years earlier.

(Reporting by Mike Scarcella; Editing by Will Dunham)