Dear Editor,We would like to share some ideas on the publication ‘COVID‐19 vaccination coverage and vaccine hesitancy among people with opioid use disorder in Barcelona, Spain’ [1]. More than two‐thirds of the sample of persons with opioid use disorder were fully vaccinated, according to Vallecillo et al., but among people with opioid use disorder on opioid agonist therapy who were referred to vaccination clinic sites, complacency and convenience were significant barriers to completing vaccination [1]. Acceptance of COVID‐19 immunisation is regulated by several factors, and the pattern may vary according to the environment and outbreak level. Furthermore, as data on vaccine efficacy and safety change, adoption trends may shift dramatically [2]. And indeed, according to a recent study, acceptance patterns are shifting over time [3]. To examine the impact of vaccination willingness and associated factors, a longitudinal study rather than a cross‐sectional analysis might be useful.