COVID-19 partners Pfizer and BioNTech have been unable to recruit healthy adults aged 50 to 64 fast enough to deliver relevant post-marketing data. Moderna is apparently also facing enrollment challenges.
Pfizer and BioNTech have stopped enrollment in a large U.S.-based trial of their updated COVID-19 vaccine in response to slow enrollment.
The study was designed to recruit 25,000 to 30,000 healthy adults aged 50 to 64. However, Pfizer reportedly closed enrollment March 6 after reviewing epidemiological trends, Reuters reported on Wednesday.
The drugmaker told trial investigators March 30 that it would stop surveillance for signs of COVID-19 illness in the study after April 3.
Pfizer and BioNTech told Reuters they are halting the study because slow enrollment is preventing them from generating relevant post-marketing data on the vaccine. “This is a very difficult population to recruit,” an unnamed executive at a contract research organization involved in the trial added on the condition of anonymity. People with chronic conditions such as hypertension or diabetes were ineligible for the study.
“Even when patients are willing to participate in COVID studies, more than 80% fail at prescreening because they don’t meet the health criteria,” the executive told Reuters. “It’s been a real challenge to enroll enough patients, particularly given the scale of these trials.”
The news comes after the FDA imposed new requirements on COVID-19 vaccines last year. In May, the agency announced it would require data from placebo-controlled trials to inform decisions about whether to support the use of COVID-19 vaccines in people aged 50 to 64. Neither Pfizer and BioNTech’s Comirnaty nor Moderna’s Spikevax and next generation mNEXSPIKE has full approval in this age group.
Moderna is also running a COVID-19 vaccine trial in people aged 50 to 64. Sources at four sites involved in the study told Reuters that the company is also facing enrollment challenges. Moderna has yet to comment on the trial’s enrollment rate, although commercial challenges in the U.S. vaccine market could suggest a dip in the number of people interested in the trial.
Moderna’s plan for 2026 foresees U.S. sales potentially dropping from $1.2 billion to roughly $1 billion, CFO James Mock said at a TD Cowen event in March. The forecast follows political and regulatory pressure. In February, the FDA refused to review Moderna’s application for an mRNA-based flu vaccine, saying the company failed to support mRNA-1010 with an “adequate and well-controlled” trial. The main point of contention had to do with the comparator vaccine used in older adults. However, the two parties ultimately came to an agreement in which Moderna would resubmit its application based on age. A decision is due in August.
Discussing the FDA and Health Secretary Robert F. Kennedy Jr. at an event in December, a Piper Sandler analyst said it “really feels like they’ve declared war on mRNA vaccines.”
