Background <p>The effectiveness of vaccines in protecting against disease wanes with increasing age. There is some evidence that psychological wellness and vitamin D supplementation can increase vaccine effectiveness in older people. This study was designed to pilot the acceptability of, and compliance with, study procedures intended for a future large randomised controlled trial (RCT). The procedures included a positive mood intervention (PMI), the use of vitamin D supplements and self-collection of finger-prick blood samples.</p> Methods <p>Twenty-eight adults aged &gt; 65 years were randomised to one of four conditions: (1) PMI and vitamin D supplements, (2) PMI only, (3) Vitamin D supplements only and (4) Usual care. Blood samples were taken before vaccination with the standard seasonal influenza vaccine and again after 28 days. Vitamin D levels and antibodies to influenza were compared before and after the participants received the allocated intervention.</p> Results <p>Good compliance with study procedures, as measured by participant responses to a Short Message Service (SMS) text or email, suggest methods were acceptable and feasible in this population. Self-collection of finger-prick samples to measure antibody responses was accomplished by 16 out of 26 participants (62%).</p> Conclusions <p>This study demonstrates that a large-scale RCT to evaluate two interventions promoting vaccine effectiveness in older adults is feasible. Simple methods of determining patient-reported outcomes and limiting study visits are acceptable to participants and may reduce costs. The finger-prick capillary sampling procedure requires refinement before wider deployment.</p> Trial registration <p>ISRCTN 12950625 08 FEB 2024 (registered retrospectively).</p>