The Burden of Influenza on the US Older Population: A Real-World Health Outcomes Study

ESWI Conference 2020

Samson S., Maier M., Lee W., Foschini L., Liska J., and Burlet N.

Evidation partnered with Sanofi to evaluate the burden of influenza on the US older population (age ≥ 50) using real world data. It was found that after the diagnosis of influenza, older adults experienced an increase in health service usage, respiratory illnesses, and non-respiratory conditions compared to the controls. Our research was presented at the ESWI 2020 conference suggesting that influenza creates significant disease burden among older adults, and highlights the need to improve vaccination rates. This important work continues to demonstrate why it is critical for not only the younger but older populations to get the flu vaccination, especially as the world undergoes flu season and COVID-19.

BACKGROUND: Studies of the influenza burden on the older population use limited sets of outcomes and often focus on specific groups such as hospitalized patients. We report a population-based analysis of influenza among older adults on real-world outcomes including diagnosis rates and healthcare visits.

METHODS: The associations between influenza diagnosis exposure on a broad set of medical outcomes was measured in a cohort of older individuals (age ≥ 50) using claims records. Individuals without influenza seen for routine office visits within the same week and age group were used as a control cohort. Claims records were retrospectively sourced from a US health plan (during the 2015-2017 influenza seasons) offering a digital wellness platform with connected wearable devices (capable of tracking steps, sleep, and heart rate). Outcomes measured were medical diagnoses (mapped to Healthcare Cost and Utilization Project (HCUP) categories), intensive care unit procedures, medication use and health care visits. Difference-in-difference (DiD) models were employed to isolate the effect of influenza outside detection, seasonal, or other measured biases. A q-value (false discovery adjusted p-value) threshold of 0.05 was used to control for multiple testing.

RESULTS: 7,262 influenza episodes and 177,157 controls (mean age 57.1 and 56.9 respectively, 56% female and 67% female respectively, p-value < 0.001 for both comparisons). 298 health outcomes (282 diagnoses, 5 inpatient procedures, 7 health services outcomes and 4 day-level activities) were assessed. In the week after influenza infection, we observed a greater use of health services, respiratory illnesses and a number of non-respiratory conditions, such as congestive heart failure, other heart diseases, syncope and sepsis syndromes compared to controls. Negative controls had more primary care related diagnoses. Sensitivity analysis by removing outcomes on the day of influenza diagnosis led to reduced DiD values and spurious clinical findings.  

CONCLUSIONS: We report on a causal model of influenza among adults older than 50 on a diverse set of health outcomes with a systematic DiD approach. There was increased health services usage, respiratory illnesses, and non-respiratory conditions among older adults in the period after influenza diagnosis. We also identified primary care related outcomes among negative controls. These findings suggest that influenza imposes a substantial disease burden among older adults and highlights the need to improve vaccination rates.