Summary of the 2018-2019 influenza season among Department of Defense service members and other beneficiaries.

The Armed Forces Health Surveillance Branch conducts weekly surveillance of influenza activity among Department of Defense (DoD) populations each influenza season. This report provides a summary of the data from the 2018-2019 influenza season. Ambulatory data for influenza-like illnesses (ILIs), influenza hospitalization data, and lab data for influenza-confirmed cases were used for the surveillance. The 2018-2019 season differed from past seasons in that it was much longer, had a later peak, and the predominant strain of influenza changed from influenza A(H1N1)pdm09 at the beginning of the season to influenza A(H3N2) in the middle of the season. Non-service member beneficiaries accounted for the majority of ILI-related encounters and hospitalizations. However, there were still 149 influenza-related hospitalizations among service members during the 2018- 2019 season. Continued weekly surveillance of influenza among DoD populations is crucial to track increases in activity each season and the potential emergence of new and/or severe influenza subtypes.