Past Seasons’ Flu Season Severity Assessments

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This page includes information about the past flu seasons’ severity assessments, including a table describing the seasonal assessment by age group and across all ages. Information on how severity is assessed each season can be found at: How CDC Classifies Flu Severity

Based on methods described on “How CDC Classifies Flu Severity”, CDC researchers classified seasonal severity from the 2003-2004 through the 2022-2023 flu seasons (the severity of the 2020-2021 season was not assessed because of very low levels of flu activity). Overall, five seasons were classified as low severity, 11 as moderate, three as high, and none as very high. Seasonal severity varies by age group. Older adults (≥65 years) experienced four seasons classified as high severity, the most seasons classified as high severity among the age groups assessed. Children (0-17 years) were the only age group to experience two seasons classified as very high severity. Adults (18-64 years) experienced two seasons classified as high severity.

CDC also shares in-season severity assessments, which are available weekly throughout the flu season at Preliminary In-Season Severity Assessment page.

Table 1. Influenza Season Severity Classifications, by Season and Age Group, United States, 2003–2004 to 2022–2023* Influenza Seasons.

*2020-2021 flu season was not estimated because of minimal flu activity.