Pfizer, BioNTech Halt U.S. COVID Shot Trial After Failing to Recruit Participants
A major U.S. clinical trial for an updated COVID shot developed by Pfizer and BioNTech has been halted after the companies failed to recruit enough participants, according to Reuters—marking a significant setback for efforts to expand use of these products in healthy populations.
The trial was designed to study healthy adults aged 50 to 64, a group increasingly targeted for ongoing booster recommendations. However, despite plans to enroll 25,000 to 30,000 participants, the study fell far short of its recruitment goals and was ultimately shut down in early March.
Strict eligibility requirements played a major role. Participants had to meet a narrow definition of “healthy,” excluding those with common conditions such as hypertension or diabetes. As a result, more than 80% of potential volunteers were screened out, drastically reducing the pool of eligible participants and slowing enrollment to a standstill.
The failure to recruit comes amid a broader and ongoing trend: declining demand for COVID shots. During the 2025–2026 season, only about 18% of Americans received an updated dose, reflecting a continued drop in public uptake.
At the same time, regulatory expectations are tightening. The U.S. Food and Drug Administration (FDA) now requires large, placebo-controlled trials for lower-risk populations, including healthy adults in this age group. These requirements are intended to generate more robust data—but also make trials significantly harder to complete, particularly when participation is low.
Without sufficient enrollment, the study could not proceed as planned.
A similar study by Moderna is currently underway but is reportedly facing comparable recruitment challenges, suggesting the issue is not isolated to a single company, but reflects a broader shift in public willingness to participate in COVID shot trials.
Too many of us watched our parents and grandparents decline or pass away following the COVID injections. So from our view, this is a VICTORY.
Source:
Reuters, Exclusive: Pfizer, BioNTech halt US COVID vaccine study after recruitment struggles
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