Vaccine uptake and barriers to vaccination among at-risk adult populations in the United States

This systematic literature review by Kolobova and colleagues provides an extensive assessment of vaccine uptake and barriers to adult immunization across seventeen at-risk populations in the United States between 2010 and 2020. The authors identify 153 publications addressing vaccination outcomes, forming one of the most comprehensive syntheses of adult risk-group vaccination in the US. Their work is grounded in the life-course immunization framework, emphasizing that at-risk populations—those with chronic diseases, immunocompromising conditions, occupational exposures, or behavioral and social vulnerabilities—bear disproportionately high morbidity and mortality from vaccine-preventable diseases. Despite longstanding national goals to improve adult vaccination, the review highlights consistently suboptimal coverage levels, often far below the Healthy People 2020 benchmark of 60%.

Across nearly all risk groups, vaccine uptake varied significantly by socioeconomic factors, healthcare access, demographic characteristics, and disease severity. Pregnant women and healthcare workers (HCWs) were the most-represented populations in the literature. Among HCWs, influenza vaccine uptake ranged widely (32%–92%), with higher uptake associated with hospital employment, mandatory vaccination policies, and free on-site vaccination programs. Nevertheless, safety concerns and opposition to mandates persisted among subgroups, indicating structural and attitudinal divergence within the workforce. Tdap coverage among HCWs also showed improvement following local mandates, underscoring the impact of institutional policy interventions.

Pregnant women demonstrated substantial variability in uptake of influenza (36%–75%) and Tdap vaccines (14%–58%). Consistent across numerous studies, provider recommendation emerged as the strongest determinant of maternal vaccination. Safety concerns for both mother and fetus—often aggravated by inconsistent counseling—were major barriers. The discrepancy between self-reported and medically documented vaccination further hints at inaccuracies in surveillance and public health monitoring.

Chronic illness groups—including individuals with diabetes, chronic liver disease (CLD), end-stage renal disease (ESRD), and immunocompromised conditions—experienced similarly inadequate uptake. HAV and HBV vaccination rates among patients with CLD ranged from only 7% to 54%, showing slight improvements over time but remaining far below ideal levels. Among individuals with diabetes, pneumococcal uptake ranged from 37% to 53% and influenza from 41% to 80%, but again, older age often correlated with poorer uptake for vaccines other than influenza. Patients with ESRD showed wide variation in influenza, HBV, and pneumococcal vaccine receipt, with racial and socioeconomic disparities persisting. Strikingly, very few studies in these clinical high-risk groups evaluated barriers to vaccination, revealing a critical knowledge gap.

Populations categorized by behavioral, social, or structural risk—such as migrants/immigrants, injection drug users (IDUs), men who have sex with men (MSM), and travelers—also exhibited consistently low uptake across multiple vaccines. Migrants and immigrants faced financial barriers, limited English proficiency, lack of insurance, and difficulty navigating healthcare systems. MSM showed low uptake of HBV, HPV, and meningococcal vaccines, with disclosure barriers (non-disclosure of sexual identity to providers), lack of targeted recommendations, and inadequate awareness contributing to under-vaccination. Among travelers, refusal was often linked to perceived low risk of disease or concerns over cost.

Across nearly all groups, four core barriers emerged repeatedly:

1. Concerns about vaccine safety and effectiveness, often amplified by misinformation.
2. Lack of insurance or high out-of-pocket costs, despite the Affordable Care Act’s partial mitigation of financial obstacles.
3. Insufficient provider recommendation, one of the most influential determinants of uptake.
4. Low risk perception and limited knowledge of guidelines.

The review makes a strong case for adopting a national life-course vaccination framework that integrates public education, clinician training, improved data systems, and removal of financial barriers. The authors argue that adult immunization remains far less structurally supported than pediatric programs, resulting in systematically missed opportunities.

Critical opinion

Kolobova et al. provide a rigorously conducted and highly valuable synthesis, especially in its breadth across diverse at-risk groups. The review’s methodological strengths include duplicate screening, a decade-long scope, and attention to gray literature. However, limitations arise from the heavy reliance on self-reported data and the heterogeneity of study designs, which complicate cross-population comparisons. More importantly, the review exposes a profound research imbalance: many of the most clinically vulnerable groups (e.g., CLD, ESRD, IDUs) have little published evidence addressing why under-vaccination persists. This gap suggests that the US immunization research agenda prioritizes convenience samples—such as pregnant women and HCWs—over populations facing the highest structural inequities. Additionally, while the authors highlight provider recommendation as a key determinant, they stop short of analyzing the systemic, institutional, and political factors that shape provider behavior and patient access. Ultimately, the review’s findings underscore the need for more equity-focused policy research and interventions that target the structural determinants of adult under-vaccination, rather than focusing predominantly on individual attitudes or knowledge gaps.

By Health Literacy Asia