Pfizer, BioNTech Halt US Study of Updated COVID-19 Vaccine

‘This study is not ending as a result of any safety or benefit-risk concerns,’ a spokesperson said.

A pharmacist prepares a Pfizer-BioNTech COVID-19 vaccine in Los Angeles on Oct. 24, 2025. Patrick T. Fallon/AFP via Getty Images

Pfizer and its German partner BioNTech are ending a clinical trial they agreed to run in 2025 when receiving approval from U.S. authorities for their updated COVID-19 immunization.

A BioNTech spokesperson confirmed on April 2 that the companies are halting the trial, which was slated to compare healthy vaccine recipients with placebo controls to evaluate the safety and efficacy of the vaccine.

“Notably, this study is not ending as a result of any safety or benefit-risk concerns,” the spokesperson told The Epoch Times in an email. “We intend to stop the study due to slow enrollment and therefore the inability to generate relevant post-marketing data. We will inform the public about any updates in due time.”

Pfizer did not respond to requests for comment by the time of publication.

BioNTech said the companies have informed the U.S. Food and Drug Administration about halting the trial. The FDA did not return an inquiry.

The FDA in mid-2025 withdrew emergency authorization for COVID-19 vaccines from Pfizer-BioNTech, Moderna, and Novavax. Regulators then issued updated approvals for the shots, which contain updated formulations to try to boost effectiveness.

Pfizer and BioNTech committed to running a randomized, double-blind, placebo-controlled trial to evaluate safety and efficacy in adults aged 50 to 64 without conditions that place them at higher risk of severe COVID-19, an FDA official said at the time.

BioNTech estimated that the trial, which was set to run at sites across the United States, would run through July 2026 and enroll 25,500 people, some of whom would receive a placebo.

Individuals would be excluded if they'd had COVID-19 in the 90 days before their first visit, or received a COVID-19 vaccine in the previous three months. Individuals would be included only if they were healthy and a physician signed off on their participation.

Dr. Christos Argyropoulos, chief of nephrology at the University of New Mexico, said on X that he was approached to take part and was deemed ineligible in prescreening.

“The inclusion and exclusion criteria are just ridiculous, and either both companies botched study design or the FDA asked them to study the [vaccine] in [unattainable] populations,” he wrote.

The FDA in 2025 approved the Pfizer-BioNTech vaccine for people aged 65 and up, as well as people aged 5 to 64 with a risk condition, such as obesity. Pfizer, BioNTech, Moderna, and Novavax agreed to run trials on other populations.

After the FDA issued the updated approvals, the Centers for Disease Control and Prevention shifted broad COVID-19 vaccine recommendations to stating that people who desired a vaccine should first consult with a health care professional and take into account individual factors as well as the risks and benefits of the shots, which have a side effect profile that includes heart inflammation.

A federal judge in March stayed that, and other changes to CDC vaccine recommendations, and the government has not yet appealed the ruling.

Jessica Adams, a former FDA medical officer, said in a social media post that the failure to find enough people for the Pfizer-BioNTech trial “raises real doubts about approval for healthy <65.”

She referenced how FDA officials have said they would not approve COVID-19 vaccines for healthy people under 65 absent trial data showing benefits of the shots outweigh the risks. “If randomized trials in that group aren’t feasible, and real-world evidence isn’t sufficient under the current framework ... it’s not clear what path remains,” she wrote.