Sachiko Ozawa, PhD, MHS, on Defining Hard-to-Reach Populations for Vaccination

The difference between “hard-to-reach” and “hard-to-vaccinate” populations is unclear based on current literature. However, a clear definition is needed to assess the target population size and appropriate vaccination interventions. A new review1 aimed to clear up these definitions.

To gain more insight on the findings of this study, Consultant360 reached out to lead author Sachiko Ozawa, PhD, MHS, who is an associate professor of practice advancement and clinical education at the Eshelman School of Pharmacy at the University of North Carolina in Chapel Hill, North Carolina.

CONSULTANT360: You and your colleagues aimed to better define the populations that remain unvaccinated. Which patient populations are currently defined as “hard-to-reach” vs “hard-to-vaccinate”?

Sachiko Ozawa: Broadly speaking, populations that have not received all recommended doses of vaccines may be considered “hard-to-reach” or target populations for “reaching the last mile” or “reaching every child” campaigns. But it is difficult to know how many people are not fully vaccinated, for which vaccines, and due to which reason(s). To date, a distinction has not been made regarding populations that face supply barriers to vaccination, demand barriers to vaccination, or both. This distinction is important because these populations face different needs. 

C360: What steps need to be taken to ensure a global definition of these terms is determined?

SO: We conducted a review to look for definitions of hard-to-reach populations for vaccination and found none that were comprehensive. We offer a potential suggestion based on the literature describing how populations may face various barriers to vaccination. We propose that hard-to-reach populations be defined as those facing supply-side barriers to vaccination due to geography by distance or terrain, transient or nomadic movement, health care provider discrimination, lack of health care provider recommendations, inadequate vaccination systems, war and conflict, home births or other homebound mobility limitations, or legal restrictions. We distinguished these from hard-to-vaccinate populations, who are reachable but difficult to vaccinate due to distrust, religious beliefs, lack of awareness of vaccine benefits and recommendations, poverty or low socioeconomic status, lack of time to access available vaccination services, or gender-based discrimination.

We believe it is important that the definition not name specific populations but focus on the mechanisms that make populations difficult to reach for vaccination. We hope this helps policymakers, governments, donors, and the vaccine community better strategize, plan, and allocate resources for interventions and remove existing barriers to vaccination.

C360: In your opinion, what needs to be done to ensure hard-to-reach and hard-to-vaccinate populations are reached?

SO: Different solutions are available to reach populations facing demand vs supply barriers to vaccination. Hard-to-reach populations, or individuals facing supply-side barriers to vaccination, may need better ways to access vaccines. For example, using new modes of transportation, such as drones, could help reach populations that are hard to reach due to geography by distance or terrain. Nationally or regionally integrated vaccine information tracking systems could help improve vaccination coverage for people who move around (eg, migrants, nomadic groups), or for individuals who are not consistently receiving health care provider recommendations. Health care workers need to be mindful not to engage in discriminatory practices and improve immunization recommendations. 

 On the other hand, hard-to-vaccinate populations, or individuals facing demand-side barriers to vaccination, may need better ways to make vaccines acceptable. For example, community-based education programs may be carried out to raise awareness, reduce distrust, or involve religious leaders to accommodate vaccination. Incentives can be deployed to increase the use of vaccination among individuals with socioeconomic hardship or debilitating time constraints preventing vaccination. 

C360: What are your tips for how providers can build trust with their patients?

SO: Providers build trust with their patients to deliver routine clinical care—and vaccines are no different. Research suggests that it is important for providers to treat vaccination as standard health care and normalize it as part of routine care, just like taking patients’ temperature and blood pressure. Engaging in announcements with patients who are ready to be vaccinated or are ready to vaccinate their children have been found to be more effective than engaging patients in open-ended conversations about vaccination.2 For patients who may have concerns, providers should then spend time answering patients’ questions and encourage patients to obtain information from reliable sources.  

C360: With this year’s influenza season on the horizon, what are your thoughts on vaccine hesitancy? How can providers overcome vaccine hesitancy, especially regarding the influenza vaccine?

SO: The World Health Organization’s Strategic Advisory Group of Experts working group has identified 3 “C”s of vaccine hesitancy.3 The group notes that vaccine-hesitant individuals may lack Convenience (do not have easy access), have limited Confidence (do not trust the vaccine or provider), or are Complacent (do not perceive a need or value of the vaccine). Evidence suggests that many individuals may be in the complacent group, where they may benefit from good provider recommendations. It is especially important for providers to not assume that all vaccine-hesitant individuals are alike.



  1. Ozawa S, Yemeke TT, Evans DR, Pallas SE, Wallace AS, Lee BY. Defining hard-to-reach populations for vaccination. Vaccine. 2019;37(37):5525-5534.
  2. Brewer NT, Hall ME, Malo TL, Gilkey MB, Quinn B, Lathren C. Announcements versus conversations to improve HPV vaccination coverage: A randomized trial. Pediatrics. 2017;139(1):e20161764.
  3. MacDonald NE; SAGE Working Group on Vaccine Hesitancy. Vaccine hesitancy: definition, scope and determinants. Vaccine. 2015;33(34):4161-4164.