Temporal patterns and potential missed opportunities in pneumococcal vaccination among adults with diabetes: A population-based cohort study

Pneumococcal vaccination is recommended for adults with diabetes because of their increased risk of pneumococcal disease, yet uptake remains suboptimal. This population-based retrospective cohort study assessed temporal patterns and factors associated with first recorded pneumococcal vaccination among adults with diabetes in the Romagna Local Health Authority, Italy, using linked administrative healthcare databases. We included 77,138 individuals (57,113 prevalent and 20,025 incident cases) followed through June 30, 2024. Monthly coverage was estimated using a person-time approach; time to vaccination and associated factors were examined using Kaplan-Meier, Cox, and competing-risks methods. Coverage increased from 7.2% in January 2017 to 28.0% in June 2024 but remained below 30%, with the largest monthly gains occurring during influenza vaccination seasons. In the incident cohort, the estimated cumulative probability of vaccination was 4.4% at one year, 12.6% at three years, and 34.8% at seven years, without a marked early increase after cohort entry. Age showed the strongest association with uptake, peaking at 60-69 years. Foreign citizenship was associated with markedly lower uptake, while associations with sex and comorbidity were more modest; comorbidity-related estimates were attenuated or reversed when death was treated as a competing event. Contextual factors showed limited associations. Recorded pneumococcal vaccination was low and delayed. The temporal pattern was compatible with incomplete integration into diabetes care pathways and suggested potential missed opportunities for timely vaccination, although the responsible mechanisms could not be distinguished. Systematic assessment at predefined healthcare contacts should be evaluated to reduce vaccination delays.