Ensuring Vaccine Efficacy and Safety Requires a Diverse Participant Population

The timeline for vaccine development is lengthy, often taking years to determine efficacy and safety. During a pandemic, resolution of the disease before a vaccine is approved can put development on hold indefinitely.

Participant recruitment and engagement can help shorten the timelines by identifying and enrolling relevant, motivated participants and ensure that the vaccine works and is safe for everyone who needs it.

Vaccine Hesitancy

Vaccine hesitancy has existed since vaccines were first introduced, with the World Health Organization (WHO) including it in the top ten threats to global health in 2019.1 In a global survey we conducted in April, at the start of the pandemic, although 85% of the respondents agreed that “vaccines are safe, effective and save lives,” only 40% reported being likely to participate in a trial for a vaccine. Similarly, in recent polls about a COVID-19 vaccine, 20-24% of people in the US said they will not be vaccinated, and an additional 11-31% say they are unsure if they will be vaccinated.2,3

Recruiting and Enrolling Participants

Finding willing and motivated participants therefore becomes key to ensure timely recruitment and enrollment. Standard methods of advertising on social media platforms or accessing a database do not adequately and quickly find the participants you need. This is where the power of big data can be particularly helpful.

Based on your protocol, global real-world data sources can be queried to form a small sample that matches your criteria (or a seed model). Then, this representative sample can be fed back into those data sources to find a larger population that looks like your seed model. From this larger population, targeted advertising and other communication methods can be used to raise awareness of your trial and attract participants. Qualifying these participants using questionnaires and professionals trained in your protocol helps to identify the participants that are most likely to enroll and remain engaged with the trial until completion. Even better, methods to track participants through to randomization provides feedback on the effectiveness of your recruitment methods.

Ensuring a Diverse Population

While diversity (or lack thereof) has been a topic of discussion in clinical research for a some time, COVID-19 has amplified the issue4 because of its disproportionate effect on the elderly and racial and ethnic minorities. Drugs and vaccines are often approved based on data from a relatively homogenous population, despite awareness that determination of their safety and efficacy requires that trials have broad representation of all ages, races, ethnic groups, and genders that could benefit from the drug or vaccine.

Real-world data also play a role in identifying participants that meet all the necessary demographic characteristics that will help ensure we can meet the above goal. Because the data sources also have information such as age, race and gender, the seed model and larger population can include a diverse set of potential participants.

Equally important is addressing underlying reasons for a lack of participation from underserved communities, including lack of awareness about trials, vaccine-related misunderstanding, fear, and the burden of participating. Engaging health care providers in the local communities, who are trusted by their patients, can help with this and should also be considered in the recruitment strategies.  

Engaging and Retaining Participants

Another challenge with vaccine trials is the necessary long-term follow-up and potentially multiple doses. Participant attrition can be particularly challenging. Digital engagement platforms and SMS-based messaging, such as notifications of upcoming study visits, are effective at keeping participants engaged. In addition, a centralized method for investigator teams to track participants through the study and efficiently engage participants during long-term follow-up can drive retention.

Read about the participant recruitment services we’re providing to increase diversity for several COVID-19 vaccine trials funded by the Biomedical Advanced Research and Development Authority (BARDA).


  1. World Health Organization. Ten threats to global health in 2019. March 21, 2019. Available at https://www.who.int/vietnam/news/feature-stories/detail/ten-threats-to-global-health-in-2019. Accessed October 6, 2020.
  2. AP-NORC. Expectations for a COVID-19 Vaccine. Available at https://apnorc.org/projects/expectations-for-a-covid-19-vaccine/. Accessed October 6, 2020.
  3. Ax J, Steenhuysen J. Exclusive: A quarter of Americans are hesitant about a coronavirus vaccine – Reuters/Ipsos poll. May 21, 2020. Available at https://www. reuters.com/article/us-health-coronavirus-vaccine-poll-exclu/exclusive-a-quarter-of-americans-are-hesitant-about-a-coronavirus-vaccine-reuters-ipsos-poll-idUSKBN22X19G. Accessed October 6, 2020.
  4. Chastain DB, Osae SP, Henao-Martínez AF, et al. Racial Disproportionality in Covid Clinical Trials. N Engl J Med 2020; 383:e59. doi: 10.1056/NEJMp2021971

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October 8, 2020