METHODS
Institutional review board approval for the US Hospitalized Adult
Influenza Vaccine Effectiveness Network (HAIVEN) study was obtained from
the University of Michigan. Cases were identified from 2017-2018 and
2018-2019 enrollees from a single site of the HAIVEN study, encompassing
two major hospital systems in southeast Michigan (Michigan Medicine
Hospital, Ann Arbor and Henry Ford Hospital, Detroit). Inclusion
criteria for the HAIVEN cohort have been described
elsewhere15,19. Briefly, adult patients ≥18 years of
age were eligible for participation if they presented to the hospital
within 10 days of symptom onset or worsening and had a diagnosis or
chief complaint broadly consistent with an acute respiratory illness
such as influenza or pneumonia. Patients were prospectively recruited
and completed a brief interview and research-assistant performed
specimen collection to determine laboratory-confirmed influenza illness.
Only individuals who tested positive for influenza were included in our
analysis.
All participants were interviewed in-person at the time of study
enrollment by research personnel. Data obtained from the electronic
health record (EHR) via trained research staff chart review or database
queries included demographics and comorbid conditions, acute illness
characteristics such as symptom duration/type, laboratory and
physiologic measures, and outcomes including ICU admission and hospital
length of stay15,19.