Vaccination Coverage: An Ongoing Public Health Challenge
When one looks at global morbidity and mortality rates over the last century, three major innovations stand out as the biggest drivers in reducing the impact of infectious disease: establishment of public health/sanitation authorities, antibiotics, and vaccination [Fig. 1].
All three of these pillars are now under threat. Public health departments have been chronically underfunded for decades, and outside of major emergencies public health is poorly prioritized [1]. Antibiotic resistance is proliferate and we are now seeing microorganisms that are effectively immune to all known antimicrobial treatments [2]. Vaccines, long held to be safe and effective prophylaxis, are increasingly targets of mistrust and misinformation, especially in the wake of the COVID-19 pandemic, and vaccination rates have declined in recent years, due to a number of reasons.
There is no question that vaccines have saved lives in the decades since their inception. Most estimates show that, globally, vaccines have saved hundreds of millions of lives in the last 50 years alone [Fig. 2][3,4].
Despite public perception to the contrary, this also holds true with COVID-19 vaccination. The vaccines prevented an estimated 20 million deaths in the first year of availability alone (Fig. 3).
Well... that's a bit more complicated. In fact, thousands of studies have been conducted to assess vaccine hesitancy, particularly with regard to the COVID-19 vaccine. In their systematic review of reviews, Kafadar et al found that hesitancy is associated with 79 factors across four major categories: vaccine safety and effectiveness, perceived vaccine barriers, concern about the rapid development of the COVID-19 vaccine, and inadequate knowledge status for COVID-19 vaccines [6]. My own experience analyzing respondent data comparing pre- and post-pandemic vaccine perception in a group of Central Texas adults further supports the findings of Kafadar et al. As those authors note, "among the individual and group factors, the most frequently encountered factors were related to information sources, trust, and personal experiences"[6]. They end their paper by admonishing the reader that vaccine hesitancy might be reduced by providers improving trust and delivering clear, reliable messaging.
But what constitutes "clear and reliable messaging?" Isn't that what public health practitioners and clinical providers have been sharing all along?
Again, it's complicated. Studies researching associations between vaccine hesitancy and health literacy have identified the need to create distinct efforts for different target segments of the population. College students, for instance, may already have adequate general knowledge of immunization, so reducing hesitancy in this group may require stronger focus on addressing their perceived risks and fears [7]. Likewise, more general educational information on vaccination may be better suited for parents, as evidence shows that vaccination rates and schedule adherence in children both improve when healthcare providers discuss immunization with parents [7]. For those fostering mistrust in providers and health authorities, peer-based communication strategies have been shown to be effective [7]. Mistrust erodes when information is conveyed by a personal source, with relatable stories. When conspiracy theories are the basis of mistrust, directly countering the conspiracy angle may actually be more effective than communicating information on vaccination [8].
In other words, clear and reliable messaging must take population segment and context into account, in order to be effective. There is no one-size-fits-all approach when it comes to improving immunization adherence. Barriers to vaccination messaging may be further confounded by variation from one vaccine to another, as the mistrust issues related to an mRNA vaccine may not be as prevalent for other routine vaccines with a longer established history.
Moreover, sociodemographic factors also play a major role in vaccination, not only insofar as they shape issues of messaging discussed above, but also in the ways they impact resource distribution and access to care. This is evident in vaccination rates between metro and nonmetro populations (Fig. 4), between regions with different levels of development and funding (Fig. 5), between differing race/ethnicity segments (Fig. 6), and numerous other demographic categories, like age, gender, and sexuality.
So improving vaccination coverage is not simply a matter of communicating the right things to the right people at the right time, but also a problem of logistics. Messaging isn't serving its purpose if the target segment is still unable to get vaccinated due to economic or other barriers, despite willingness of a population to receive the vaccine. This problem isn't unique to immunizations; indeed, it's a problem which plagues health service delivery in general. How do we improve equity, particularly with regard to impoverished and rural populations? While some aspects of care can be addressed through decentralization of services via telemedicine and related technologies, a vaccine can't be administered through the internet. Providers will need to expand reach in a way that makes sense and is scalable: train-the-trainer activities, more non-traditional administration (pharmacists, etc.), ridesharing vouchers and methods for improving access to health centers, establishing regional hubs and streamlining logistics in dispersed populations, home health visits, etc.
Increasing vaccine uptake will remain one of the biggest hurdles facing population health workers for the foreseeable future. Any viable strategy must be based on rigorous systems thinking, tailored to the unique context of the populations comprising the region served. It must accordingly adapt its messaging and delivery tactics to surmount the myriad cultural, demographic, and stuctural/logistical challenges inherent to reaching ever-broader shares of the population.
REFERENCES
1. TFAH. (2023). The Impact of Chronic Underfunding on America’s Public Health System: Trends, Risks, and Recommendations. Trust for America's Health. https://www.tfah.org/wp-content/uploads/2023/06/TFAH-2023-PublicHealthFundingFINALc.pdf
2. WHO. (2023). Antimicrobial Resistance. World Health Organization. https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance
3. Mellis, C. (2022). Lives saved by COVID‐19 vaccines. Journal of Pediatrics and Child Health. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9537923/
4. Shattock et al. (2024). Contribution of vaccination to improved child survival: modelling 50 years of the Expanded Programme on Immunization. – processed by Our World in Data. https://ourworldindata.org/grapher/lives-saved-vaccines-region
5. Unknown. (2022). Covid-19 vaccines saved an estimated 20m lives during their first year. The Economist. https://www.economist.com/graphic-detail/2022/07/07/covid-19-vaccines-saved-an-estimated-20m-lives-during-their-first-year
6. Kafadar et al. (2022). Determinants for COVID-19 vaccine hesitancy in the general population: a systematic review of reviews. Journal of Public Health, vol 31. https://link.springer.com/article/10.1007/s10389-022-01753-9#Sec17
7. Hudson, A. & Montelpare, W.J. (2021). Predictors of Vaccine Hesitancy: Implications for COVID-19 Public Health Messaging. International Journal of Environmental Research and Public Health: 18(15). https://www.mdpi.com/1660-4601/18/15/8054
8. Jolley, D. & Douglas, K.M. (2014). The Effects of Anti-Vaccine Conspiracy Theories on Vaccination Intentions. PLoS One. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0089177#s4
9. USDA. (2021). COVID-19 vaccination rates vary by metropolitan and persistent poverty status. Economic Research Service, United States Department of Agriculture. https://www.ers.usda.gov/data-products/chart-gallery/gallery/chart-detail/?chartId=102643
10. Thrasher, R. & Ömer, Ö. (2021). Chart of the Week: Comparing Global Vaccination Rates with Populations. Global Development Policy Center, Boston University.https://www.bu.edu/gdp/2021/04/21/chart-of-the-week-comparing-global-vaccination-rates-with-populations/
11. Horton, J. (2021). Covid: How ethnicity and wealth affect US vaccine rollout. BBC. https://www.bbc.com/news/world-us-canada-56405199
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