When COVID-19 struck in early 2020, the world needed vaccines, and it needed them fast. But before any vaccine could be approved, it had to go through rigorous clinical trials. For Moderna and Pfizer, this meant enrolling tens of thousands of participants in a matter of months, something that typically takes years. How did they do it?
A Global Emergency and a New Pace for Science
Under normal circumstances, vaccine clinical trials can take 5–10 years. But the urgency of the pandemic pushed regulators, researchers, and pharmaceutical companies to rethink every step of the process, including participant recruitment.
Both Moderna and Pfizer launched Phase 3 trials in July 2020, aiming to enroll around 30,000 (Moderna) and 44,000 (Pfizer) volunteers, respectively. Recruiting such numbers usually takes many months, if not years. But by leveraging a mix of technology, public interest, and logistical innovation, both companies reached their targets in a matter of weeks.
A major factor: public willingness. With daily headlines, climbing death tolls, and a global spotlight on vaccine progress, thousands of people stepped forward to participate in what they saw as both a civic duty and a medical opportunity.
Technology and Outreach: Casting a Wide Net
Moderna and Pfizer partnered with dozens of research sites across the U.S. and abroad. They also used online registries, social media, and direct outreach to speed up the process. In the U.S., the National Institutes of Health (NIH) helped create volunteer screening tools, including the COVID-19 Prevention Network (CoVPN), to direct interested individuals to nearby clinical trial sites.
This strategy helped reach a large and diverse group of potential participants quickly. Moderna, for example, used digital recruitment platforms to monitor demographic data in real time, allowing the company to adjust recruitment goals to ensure better representation of older adults, communities of color, and people with underlying health conditions—all crucial for measuring vaccine effectiveness across different populations.
Equity and Representation: A Mid-Trial Challenge
One major challenge that both companies faced was ensuring diversity. Early in Moderna's trial, for instance, the company noted a lack of minority participants and briefly slowed recruitment in September 2020 to correct the imbalance. By the time their trial concluded, 37% of Moderna's U.S. participants were from minority backgrounds. Pfizer reported a similar figure, about 42% of its global trial population came from diverse racial and ethnic groups.
This was essential not just from an ethical standpoint, but a scientific one: COVID-19 disproportionately impacted Black, Latino, and Indigenous communities, and it was critical to understand how vaccines performed in those groups.
Conclusion: A Blueprint for Future Trials?
The speed at which Moderna and Pfizer enrolled participants in their COVID-19 trials was unprecedented, but not careless. They achieved rapid recruitment by combining public urgency, strategic outreach, and modern technology, while working under the close supervision of regulatory bodies like the FDA and EMA.
Although the pandemic was a unique situation, the lessons learned, especially about digital recruitment and diversity monitoring, may reshape how future clinical trials are designed and conducted.
In the face of crisis, the scientific community showed that with the right resources, collaboration, and public trust, even the most daunting challenges can be met faster than ever before.