Interventions to Improve Vaccination Uptake Among Adults: A Systematic Review and Meta-Analysis

Background Immunisation is an effective intervention for controlling more than 20 life-threatening infectious diseases, reducing both morbidity and mortality. One major vaccination-related achievement was the worldwide eradication of smallpox; the world was declared free of smallpox by the World Health Assembly on 8 May 1980. A second major vaccination-related success has been a reduction in wild poliovirus cases by 99.9% since 1988, from more than 350,000 incident cases that year to 30 in 2022. Objectives To assess the effects of interventions aimed at increasing vaccination uptake among adults. Search methods A search was conducted in CENTRAL, Embase Ovid, Medline Ovid, PubMed, Web of Science, and Global Index Medicus databases for primary studies, in August 2021, and updated in November 2024. Selection criteria Randomised trials, irrespective of their publication status and language of publication, were eligible for inclusion in this review. Data collection and analysis Two review authors independently screened records, assessed full-text articles to identify potentially eligible studies, extracted data, and evaluated risk of bias, resolving differences by consensus. For each included study, we calculated risk ratios (RR) with 95% confidence intervals (CI). We pooled study results using random-effects meta-analyses and used GRADE to assess the certainty of the evidence. Main results Thirty-five randomised controlled trials met the inclusion criteria and were included in the review, the majority of which were conducted in the United States of America (U.S.A.). The interventions were aimed at improving vaccination uptake among adults aged 18 years and above who were eligible for vaccination. Most of the studies assessed uptake of influenza vaccine (18 studies), with the rest investigating a variety of vaccines, including hepatitis A virus, coronavirus disease of 2019 (COVID-19), hepatitis B virus, pneumococcal, tetanus, diphtheria, and pertussis (Tdap), herpes zoster (the acronym would be either: herpes zoster vaccine (HZV) or recombinant zoster vaccine (RZV) or live shingles zoster vaccine (ZVL) ), and human papillomavirus (HPV) vaccines (18 studies). Our results indicate that letter reminders were slightly effective in increasing influenza vaccination uptake compared to the control (RR: 1.75, 95% CI: 0.97, 1.16; 6 studies; 161,495 participants; low-certainty evidence). There were increased levels of influenza vaccination uptake among participants who received education interventions compared to those who were in the control group (RR: 1.88, 95% CI: 0.61, 5.76; 3 studies, 1,318 participants; low-certainty evidence). Tracking and outreach interventions also increased the influenza vaccination uptake (RR:1.87, 95% CI: 0.78, 4.46; 2 studies, 33,752 participants; low-certainty evidence). Conclusion Letter reminders and education directed at recipients are effective in increasing vaccination uptake compared to the controls.