During the World Vaccine Congress, currently underway in Washington, DC, we spoke with Jose Jimeno, SVP of vaccines & infectious diseases at VaxTrials, part of the Emmes Group, about the lingering and unwelcome legacy of the pandemic. 

In a surprising twist – despite COVID-19 vaccines saving millions of lives and helping end the global crisis – vaccine trial recruitment is now more difficult than ever. Trust among potential volunteers has dropped sharply, with vaccine hesitancy reshaping public perceptions of clinical research.

One reason may lie in the nature of vaccine studies themselves. Unlike therapeutic drug trials, which typically attract individuals seeking treatment, vaccine studies rely on healthy volunteers testing preventive treatments for diseases they may never encounter. This makes their reputation for safety particularly important and places added pressure on retention strategies. Participants often struggle to see a direct personal benefit. While the pandemic raised awareness about the importance of vaccines, it also triggered a wave of misinformation—much of which has stubbornly taken root.

LL: Can you give a real-world example of this?

JJ: Hesitancy is not limited to under-resourced regions. In fact, it’s often just as prevalent in high-income countries, where widespread misinformation and mistrust in pharmaceutical companies fuel scepticism about vaccine safety and efficacy.

A relevant example is the hesitancy surrounding the human papillomavirus (HPV) vaccine. Despite its proven ability to prevent cervical cancer, public concern over alleged side effects led to plummeting uptake in countries like Japan and Denmark. Similarly, during the COVID-19 pandemic, misinformation drove distrust and contributed to lower-than-expected vaccine uptake in many developed countries. These cases reflect the complex interplay of fear, misinformation, and cultural influences that continue to undermine vaccine trial recruitment globally.

LL: What are the main factors in attracting recruits?

JJ: Participation reluctance stems from multiple factors, including misinformation, cultural beliefs, scientific misunderstandings, and safety concerns.

In Latin America, for example, community altruism is often a strong motivator—particularly in regions where diseases like dengue remain endemic. However, this desire to help is tempered by fear and mistrust. Concerns about side effects and the safety of experimental vaccines weigh heavily on potential volunteers. Another key factor is access to high-quality medical care during the trial—services that may not be available through routine healthcare. Access to comparator vaccines not included in national immunization plans can also serve as a compelling incentive.

Monetary factors play a growing role too, though context is everything. In high-income regions like the US and Europe, direct payments are a clear incentive. In lower-income settings, however, such payments are often not permitted. Instead, volunteers receive reimbursement for transport or meals—modest but meaningful recognition of their time and effort, helping ensure participation is not financially burdensome and reinforcing the ethical value of their contribution.

LL: Can you give an example of how misinformation is harming recruitment today?

JJ: A persistent misunderstanding from the pandemic relates to expectations of vaccine performance. Many believed COVID-19 vaccines would entirely prevent infection, rather than primarily reduce severe illness and death. This misconception has led some to conclude that the vaccines ‘didn’t work,’ eroding trust in vaccine research.

More broadly, the volume of misinformation during the pandemic—ranging from exaggerated side effects to conspiracy theories—has created a climate of fear. The impact is evident in recruitment data. Before the pandemic, fewer than 5% of volunteers declined participation after visiting a trial site. Today, that number is closer to 30-50%, a striking increase that highlights the challenge of restoring trust in vaccine trials.

LL: Strategies for addressing recruitment challenges

JJ: Building trust is central to effective recruitment—trust in investigators, in the process, and in regulatory oversight. In Latin America and Southeast Asia, for instance, strong doctor-patient relationships are key. Trials that partner with respected physicians, local investigators, and community leaders often see greater participation. This is especially true in paediatric studies, where family and community approval carry significant weight.

Wider trust in governments and regulatory bodies also matters. Transparent and respected institutions are associated with higher enrolment rates. Having principal investigators who are both visible and trusted within the community can make a measurable difference.

Education and transparency are also vital. Clear communication about the trial process—including risks, side effects, and benefits—helps build credibility. Volunteers are more likely to trust researchers who speak openly about potential risks than those who attempt to minimize them. For example, in the OPV trials, consent forms were simplified and paired with clear explanations of the trial’s importance, helping families understand and support participation.

LL: What can be done to re-engage volunteers?

JJ: This is a key challenge, and the solution starts with addressing people’s questions, motivations, and concerns directly. Sponsors and research teams must commit to providing clear, accessible, and accurate information throughout the recruitment journey.

Beyond education, reducing the burden of participation is critical. Can trials reduce the number of required visits or eliminate unnecessary procedures? Could repeated blood draws be avoided, particularly in paediatric studies? Adjusting consent requirements to better accommodate single-parent households might also improve enrolment.

Innovative strategies such as satellite trial sites can also boost accessibility. For example, in the OPV trials, satellite locations near participants’ homes significantly reduced travel burdens and led to higher enrolment.

Ultimately, rebuilding public trust in vaccine trials requires a multifaceted approach—one rooted in transparency, accessibility, and local engagement. These efforts are essential to ensuring that critical research can continue, and future public health challenges can be met with robust scientific evidence.