Missed opportunities and co-administration patterns for influenza vaccination in older adults in Italy: a retrospective cohort study

Background: Missed opportunities for vaccination (MOV) reduce seasonal influenza vaccine (SIV) coverage among high-risk older adults who frequently access healthcare services but remain unvaccinated. Methods: We conducted a retrospective cohort study using the Siracusa Local Health Authority immunization registry in Italy. Individuals aged ≥65 years who received pneumococcal, herpes zoster, COVID-19, or respiratory syncytial virus vaccines during the 2023/24 and 2024/25 influenza seasons were assessed for SIV status. Outcomes included missed opportunities for SIV and co-administration patterns. Results: Among 4485 COVID-19, 3428 pneumococcal, 1617 herpes zoster, and 198 respiratory syncytial virus vaccine recipients, the proportion of individuals who did not receive SIV during the same influenza season (i.e., missed SIV opportunities) was 10.2%, 8.0%, 18.4%, and 7.6%, respectively. Co-administration was highest in the pneumococcal (47.6%) and respiratory syncytial virus (42.4%) cohorts, and lower in the COVID-19 (8.9%) and herpes zoster (11.0%). Older age was positively associated with SIV uptake in the COVID-19 and pneumococcal groups, while sex was not a consistent determinant, except for higher uptake among males in the RSV cohort. Conclusions: MOV were frequent among older adults who received other recommended vaccines, underscoring persistent gaps in adult immunization delivery. These findings support the need for systematic assessment of influenza vaccination status at every healthcare encounter, broader co-administration practices, and strengthened training and organizational support for healthcare professionals to optimize influenza vaccination and strengthen prevention in this vulnerable population.