Pfizer Inc (NYSE:PFE) and its German COVID-19 vaccine partner BioNTech SE (NASDAQ:BNTX) have reportedly halted recruitment for a large U.S. trial of their updated COVID-19 vaccine targeting adults aged 50 to 64, citing difficulty in enrolling enough participants.

The companies confirmed they had notified the U.S. Food and Drug Administration (FDA) of their decision.

The study aimed to enroll between 25,000 and 30,000 individuals, but fell short of that goal.

Citing a letter, Reuters noted that Pfizer said it would also stop monitoring participants for COVID-19 symptoms after April 3. Enrollment had already been closed on March 6 following a review of epidemiological trends.

Regulatory Pressure And Weak Uptake Weigh On Trials

The move underscores broader headwinds facing COVID-19 vaccine makers, including reduced demand in the U.S. and tighter regulatory expectations, Reuters reported.

The FDA last year increased requirements for vaccine approvals in the 50–64 age group, calling for large, placebo-controlled trials. As a result, no COVID-19 vaccines have been cleared for this demographic since the updated guidelines were introduced.

Lower infection rates and declining public interest in booster shots have further complicated trial recruitment and development strategies.

In December 2025, BioNTech filed a patent infringement lawsuit against Moderna Inc. (NASDAQ:MRNA), alleging that Moderna’s next-generation COVID-19 vaccine, mNEXSPIKE, relies on proprietary technology developed and patented by BioNTech.

Pfizer Secures $2 Billion Win In European Vaccine Dispute

Separately, Bloomberg reported that Pfizer secured a significant legal victory in Europe. A Belgian court ordered Poland and Romania to pay a combined 1.9 billion euros (around $2.2 billion) for COVID-19 vaccine doses they declined to accept during the pandemic.

The Brussels Court of First Instance ruled that Poland must pay approximately 1.3 billion euros, while Romania owes around 600 million euros under a 2021 contract negotiated with the European Commission.

The court determined that declining infection rates did not justify altering the agreement and rejected arguments related to pricing terms and liability clauses.

Political Fallout And Contract Enforcement

Both countries had refused delivery of allocated doses and withheld payment, prompting Pfizer to initiate legal action in 2023, Bloomberg reported on Wednesday.

Polish Prime Minister Donald Tusk criticized his predecessor, Mateusz Morawiecki, blaming prior decisions for the financial penalty.

Poland has indicated it will pursue legal avenues to challenge the ruling, while Romania is expected to respond formally.

Price Action: Pfizer shares were up 0.94% at $28.34 at the time of publication on Wednesday. The stock is trading at a new 52-week high, according to Benzinga Pro data. BioNTech shares were up 1.53% at $90.24.

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