(B-112) Trends in Outpatient Influenza Antiviral Use in US Adults: 2010-2021

Background: While prompt antiviral treatment reduces duration of illness and complications of influenza, concerns remain regarding the guideline-concordant use of these antivirals in clinical practice.

Objectives: To evaluate trends in influenza antiviral dispensing in outpatient settings among US adults following influenza diagnosis across the 2010-11 to 2020-21 seasons.

Methods: We used the Merative MarketScan Commercial Claims and Medicare Supplemental databases to identify outpatient influenza diagnoses from July 1, 2010, to June 30, 2021. Patients dispensed antivirals (oseltamivir, zanamivir, or baloxavir marboxil) within two days of diagnosis were categorized as treated. Demographic factors—including age, sex, insurance type, and US Census region—were extracted, along with selected comorbidities known to increase the risk of influenza complications. We estimated the percentage of influenza antivirals dispensed following diagnosis for each season among all individuals as well as those at high-risk for influenza complications, defined as age>65 or specific co-morbidities. Usage of antivirals across regions were also estimated. We used Joinpoint regression to assess changes in annual prescribing rate trends over time.

Results: We identified 3,717,537 influenza episodes among 3,421,125 unique patients, with 2,380,164 episodes (mean age 42.9years) meeting the enrollment criteria. Among these, antivirals were dispensed in 1,413,280 (59.4%) episodes. Among those at high-risk for influenza complications, 474,800 (56.9%) were dispensed an antiviral. Oseltamivir was the most frequently dispensed antiviral, accounting for 98% of total dispensing. Dispensing rates across seasons ranged from 23% (2020-21) to 66% (2017-18). The median rate of dispensing by month was 47.95%, and the monthly ratio relative to the median was more than 1.3-fold higher for three months (Jan, Feb, Dec) and less than 0.7 for two months (Jul, Aug). Notably, we observed differences in antiviral therapy across high-risk groups, ranging from 41% (stroke) to 58% (immune disorder). We also found regional variation ranging from 46% (Pacific region) to 67% (West-South Central). The Joinpoint analysis showed a significant increasing trend in patients receiving antivirals from the 2010-11 to 2017-18 season (4% annual percentage increase), followed by a declining trend (5% annual percentage decrease) in more recent seasons.

Conclusions: We found that a substantial proportion of individuals do not receive guideline-recommended antiviral treatment following an influenza diagnosis, and overall, antiviral prescribing has declined in recent seasons. These findings underscore the need to optimize antiviral usage to ensure timely and effective treatment.