Influenza burden among chronic condition and immunocompromised patients in the United States.

Objective: This retrospective cohort study examined influenza-like illness (ILI) in the United States during the 2017-2018 season among vaccinated adults who are immunocompromised or have high-risk chronic conditions. Results among adults with no evidence of vaccination (NEoV) were included to help contextualize study findings.

Methods: The Veradigm Network EHR linked to claims data were used to identify adults (≥18 years old) with continuous enrollment in claims between 1 October 2016 and 20 May 2018. Patients were stratified by evidence of influenza vaccination between 1 August 2017 and 6 May 2018 (vaccinated or no evidence of vaccination [NEoV]). Individuals were classified as immunocompromised or with a high-risk chronic condition based on diagnoses and treatments between 1 October 2016 through 1 October 2017. The main outcome of interest was influenza-like illness (ILI) during the influenza season.

Results: A total of 2,763,671 vaccinated individuals and 7,702,021 individuals with NEoV were identified, of whom 2.5% and 1.2%, respectively, were in the immunocompromised subgroup, while 6.7% and 3.2% had at least one high-risk chronic condition. The percentages of patients with an ILI were 2.5% and 2.7% in the overall vaccinated and NEoV cohorts, 3.1% and 3.5% in the immunocompromised subgroups, and 3.0% and 3.2 in the chronic conditions subgroups. Multivariable modeling of odds of ILI among vaccinated individuals found that chronic obstructive pulmonary disease, rheumatoid arthritis, and end stage renal disease were the diagnoses most strongly associated with increased odds of ILI.

Conclusion: There remains an unmet need for additional prophylactic agents that reduce the incidence and severity of ILI among patients who are immunocompromised or have chronic conditions.