PROTECTIVE-D—a feasibility randomised controlled trial examining the effect of a positive mood intervention and vitamin D supplementation on the immunological responses to influenza vaccination in older adults

Background 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. Methods Twenty-eight adults aged > 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. Results 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%). Conclusions 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. Trial registration ISRCTN 12950625 08 FEB 2024 (registered retrospectively).