A scoping review of randomised controlled trials of vaccines that recruited care home residents: lessons for future trials

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S Subbarayan1,2; I Smith-Dodd1; G Nicolson1; J K Burton3; J T Scott4; S S Vasan1; S D Shenkin5; R L Soiza1,2; The WATCH Consortium
1 NHS Grampian, UK; 2 Ageing Clinical and Experimental Group, University of Aberdeen, UK; 3 Academic Geriatric Medicine, University of Glasgow, UK; 4 NHS Highlands, UK; 5 Ageing and Health Research Group, Usher Institute, The University of Edinburgh, UK.
Scientific Research
SP - Other medical conditions

Abstract

Introduction
Older care home (CH) residents are particularly vulnerable to infections and often experience adverse outcomes. Despite this group being prioritised for vaccination, no COVID-19 vaccine trials recruited CH residents. Given that the social and biological characteristics of CH residents may influence vaccine effectiveness, it is crucial to test vaccines in this population.

Methods
The Widening Access to Trials in Care Homes (WATCH) project was established to develop best practice guidance on designing and conducting vaccine trials in the CH population. As part of this project, a scoping review was conducted using the Joanna Briggs Institute methodology to identify vaccine trials that recruited CH residents and reported recruitment challenges and strategies. A comprehensive search was carried out in five databases: EMBASE, MEDLINE, PsycINFO, CINAHL, and Cochrane Library, from 1990 to 2025. Three authors independently screened articles and extracted data. Results are reported as descriptive summaries.

Results
We retrieved 701 articles and included 20 studies from 11 countries. 7479 participants from 238 CHs were recruited to influenza (N=17) or pneumococcal (N=3) vaccine trials. Median sample size was 270, and the weighted mean age was 82.3 years. Screen failure and dropout rate averaged 70% (seven studies) and 8% (five studies), respectively. The two most common reasons for screen failure were residents' declining participation (46%) and not meeting eligibility criteria (27%). Death (21%) was the most common reason for dropout. Barriers identified include eligibility criteria and recruitment, consent and assent issues, ethical and regulatory concerns, CH-related factors, and study time frame and logistical factors. Facilitators identified include recruitment and data collection methods, consent and assent factors, and collaboration with CHs.

Conclusion
Our review is the first to report quantitative and qualitative evidence on barriers and facilitators to recruiting CH residents in vaccine trials. The findings will assist researchers in planning future vaccine trials in this population.