Flu season typically lasts several months, varying by region and year, but generally spans from fall through spring in temperate climates. In the Northern Hemisphere, including the US, it often runs from October to May , with peak activity between December and February. Recent data shows ongoing evolution of strains like A(H3N2), with elevated activity into early 2026.

Duration Breakdown

Flu season doesn't have fixed endpoints; it ebbs and flows with viral circulation and weather. Most outbreaks build over 3 weeks , peak, then decline over another 3 weeks locally. Nationally:

  • Standard range : October–May (about 7–8 months).
  • Peak months : Mid-winter, though post-COVID patterns have stretched this unpredictably (e.g., 2021–2022 lasted into June).
  • Current context (2025–2026) : Global rises in A(H3N2) noted since late 2025, aligning with Northern Hemisphere winter—activity remains elevated but within seasonal norms as of early January 2026.

Regional Variations

  • US/Northern Hemisphere : Fall/winter dominance due to indoor crowding and lower humidity aiding virus survival.
  • Southern Hemisphere : Peaks June–September, flipped by seasons.
  • Tropics : Year-round, less defined peaks.

Trends show flu becoming less predictable since 2020, influenced by vaccines, COVID measures, and viral drift.

Factors Influencing Length

Multiple viewpoints from health experts highlight why seasons vary:

  • Viral strains : Dominant types like H3N2 can prolong activity.
  • Vaccination rates : High uptake shortens severity, as seen in 2020–2021.
  • Public behavior : Masks and distancing once muted seasons.

| Year/Season | Start | Peak(s) | End | Notes

|
|-------------|--------|---------|-----|--------------|
| Pre-COVID (typical) | Oct | Dec–Feb | May | Standard winter burden |
| 2020–2021 | ~Oct | Low throughout | ~June | Mild due to precautions |
| 2021–2022 | Nov | Dec & Apr | June | Biphasic, extended |
| 2022–2023 | Oct | Winter | Spring | Returned to pre-pandemic levels |

Prevention During Peak

Stay protected as cases linger:

  • Get the annual flu vaccine—effective against severe outcomes even with drift.
  • Wash hands, avoid crowds.
  • Antivirals like Tamiflu shorten personal illness if started early (symptoms last 5–7 days typically).

Individual stories from forums echo this: one parent noted their family's flu dragged into March despite vax, blaming late-season surges [-inspired trends].

TL;DR : Flu season runs ~October–May in the US (7+ months), peaking mid- winter, with current 2025–2026 activity ongoing. Vaccines remain key.

Information gathered from public forums or data available on the internet and portrayed here.