1709 - Influenza Surveillance in the U.S. Department of Veterans Affairs (VA): 2019-2020 Season

Background: VA conducts annual surveillance for seasonal influenza. VA’s large elderly population is at higher risk for influenza complications, including hospitalization and death. Herein we summarize VA’s 2019-20 national surveillance data for influenza activity and vaccinations.

Methods: Influenza telephone triage, influenza-like-illness (ILI) encounters and antiviral prescriptions plus outpatient visits, laboratory testing (antibody tests excluded), hospitalizations and deaths for influenza were obtained from VA data sources (9/29/19-5/16/20) and compared to prior seasons and national CDC FluView data. Influenza vaccinations were captured starting 8/1/2019. Vaccination rates were calculated based on VA users during the fiscal year.  

Results: Surveillance metrics are presented (Table). ILI visits ranged from 0.9%-3.1% during the season. Influenza activity peaked during 2020 Weeks 6-7 and dropped rapidly beginning in Week 12, matching trends reported by CDC for influenza activity (Figure 1). Testing revealed 23,357 influenza positives out of 162,102 tests performed (14.4%). 17% of laboratory-confirmed influenza cases were hospitalized (compared to 23% during the prior season) with a median length of 3 days. Total influenza positives, telephone triage encounters, outpatient visits and antiviral use were higher than the prior season, whereas coded hospitalizations and deaths were fewer (Table, Figure 2).Table. VA Influenza Surveillance Measures, 2014-2015 through 2019-2020 Seasons.
Figure 1. Comparison of select VA and CDC Influenza Indicators. Influenza positive laboratory tests and % positive (top) and influenza hospitalizations (bottom), by Season.
Figure 2. Comparison of Key VA Influenza Indicators, by Season.


Conclusion: The 2019-20 influenza season was of moderate severity when compared to prior seasons and continues to track well with national CDC data. Overall, vaccination levels have increased modestly and high-dose/adjuvanted vaccine administration increased from 6 to 26% of total vaccine given over the seasons evaluated. Influenza activity dropped precipitously after Week 12 even though testing for influenza remained high in the setting of COVID-19. This may have been influenced by widespread social distancing and masking measures adopted in response to COVID-19.