OBJECTIVES

: The continuity of influenza vaccination is essential to the people at high risk for complications in the case of influenza infection. This study aimed to evaluate the continuity of influenza vaccination during the 2015/16 to 2017/18 flu seasons for elderly with high-risk conditions.

METHODS

: We used linked databases of the Korea Centers for Disease Control & Prevention’s vaccination registry, which contains all National Immunization Program vaccination records, and the National Health Insurance Service claims data. The patients with high-risk conditions were defined as those who visited ≥1 in inpatient setting or ≥3 in outpatient setting for the flu season, Sep 30 to Apr 30, and the preceding 8 months with diseases specified by the Advisory Committee on Immunization Practices as high-risk groups. Those who died before Apr 30, 2018 were excluded. The proportion of vaccination for each season were calculated, and the association of vaccination continuity and the types or the number of diseases were assessed by using logistic regression.

RESULTS

: A total of 1,617,546 elderly who had at least one high-risk disease and at least one flu vaccination during the three seasons were identified. Among them, 1,247,297 (77.11%) were vaccinated in all three seasons. In patients with one high-risk condition in all three seasons, people with pulmonary disease, cardiac disease, or diabetes had higher odds of vaccination continuity (Pulmonary: 1.22, 95% CI: 1.20-1.23; Cardiac: 1.15, 1.13-1.16; Diabetes: 1.15, 1.14-1.17), while patients with liver, renal, Immunodeficiency disease, or cancer were less likely to vaccinated successively. People with more than one high-risk condition during all seasons are likely to be vaccinated continuously than those with only one (1.06, 1.04-1.08).

CONCLUSIONS

: We observed that of all high-risk elderly were vaccinated in all three seasons, which means the vaccination continuity were high. Because this study used only 3 seasons, further studies using more seasons are needed.