2019–20
Flu Season

Moderately high severity, cut short in march 2020 by covid-19 interventions.

CDC FluView ILINet · Delphi CMU Epidata

Season Peak

Peak Period

Weeks Active

Dominant Strain

Week by week

Season Arc

ILI% nationally — percentage of outpatient visits for influenza-like illness, CDC FluView ILINet, Weeks 40–20.

Very High (>8%)

High (5–8%)

Moderate (3–5%)

Low (2–3%)

Very Low (<2%)

Context

How it compares

Peak ILI% nationally for recent seasons — shows where 2019–20 sits in the broader historical picture. Bar length = peak severity.

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Context

About this season

Context: The season ended approximately 4–6 weeks earlier than normal due to COVID-19 school closures and behavioral changes beginning in mid-March 2020. The truncated arc is visible in the chart.

Virology

Flu A vs. Flu B

Share of positive flu tests by type, aggregated across the full season from CDC clinical laboratory data (national).

Geography

Regional peak activity

Peak ILI activity by HHS region across the 2019–20 season — regions sorted by severity.