# When is flu season?

*February has been the peak month more often than any other in the seasons the CDC has charted since 1982-1983.*

- Type: Explainer
- Section: Health
- By: Health Desk
- Published: 2026-11-12T00:23:00-05:00
- Updated: 2026-11-12T00:23:00-05:00
- URL: https://factsdesk.com/health/when-is-flu-season/

Topics: [CDC](https://factsdesk.com/topic/cdc/)

## Key facts

- Flu season in the United States usually occurs in the fall and winter, and flu activity most often peaks between December and February, according to the CDC. Source: [Centers for Disease Control and Prevention](https://www.cdc.gov/flu/about/season.html). Confirmed 2026-11-12T00:22:00-05:00. Cite: https://factsdesk.com/health/when-is-flu-season/#flu-season-in-the-united-states-usually-occurs-in-the-fall
- In the CDC's chart of the 1982-1983 through 2023-2024 seasons, flu activity most often peaked in February (17 seasons), followed by December (7), January (6) and March (6). Source: [Centers for Disease Control and Prevention](https://www.cdc.gov/flu/about/season.html). Confirmed 2026-11-12T00:22:00-05:00. Cite: https://factsdesk.com/health/when-is-flu-season/#in-the-cdc-s-chart-of-the-1982-1983-through-2023-2024
- Seasonal flu viruses are detected year-round in the United States, the CDC says. Source: [Centers for Disease Control and Prevention](https://www.cdc.gov/flu/about/season.html). Confirmed 2026-11-12T00:22:00-05:00. Cite: https://factsdesk.com/health/when-is-flu-season/#seasonal-flu-viruses-are-detected-year-round-in-the-united
- The CDC says September and October are generally good times to be vaccinated against flu and that, ideally, everyone should be vaccinated by the end of October. Source: [Centers for Disease Control and Prevention](https://www.cdc.gov/flu/vaccines/keyfacts.html). Confirmed 2026-11-12T00:22:00-05:00. Cite: https://factsdesk.com/health/when-is-flu-season/#the-cdc-says-september-and-october-are-generally-good-times

Flu season in the United States usually occurs in the fall and winter, and flu activity most often peaks between December and February, according to the [Centers for Disease Control and Prevention](https://www.cdc.gov/flu/about/season.html). The agency says seasonal flu viruses are detected year-round in the United States, and that influenza viruses typically circulate during the fall and winter.

## Which month flu peaks

The CDC [charts the peak month](https://www.cdc.gov/flu/about/season.html) of each flu season from 1982-1983 through 2023-2024. It defines the peak month as the month with the highest percentage of respiratory specimens testing positive for influenza virus infection. February was the peak month most often.

| Peak month | Seasons |
| --- | --- |
| February | 17 |
| December | 7 |
| January | 6 |
| March | 6 |

The CDC says there was no discernible peak in flu activity during the 2020-2021 season, because the level of influenza virus circulation that season was uncharacteristically low.

## How the CDC tracks the season

The CDC publishes flu activity in a weekly surveillance report called FluView and in a tool called FluView Interactive. The agency [says](https://www.cdc.gov/flu/about/season.html) the data it collects are used to update both on the following Friday, and it describes a week-long delay between the collection of flu surveillance data and its reporting.

Flu is not the only virus that spreads at this time of year. The CDC's flu season page says other respiratory viruses circulate during flu season too, including the virus that causes COVID-19 and respiratory syncytial virus (RSV), which it describes as the most common cause of severe respiratory illness in young children. The level of respiratory illness that the CDC reports for each state this week is on the page [Is flu and respiratory illness high in my state?](/health/is-flu-and-respiratory-illness-high-in-my-state/)

## When the CDC says to get a flu vaccine

The CDC [says](https://www.cdc.gov/flu/vaccines/keyfacts.html) that everyone 6 months and older in the United States, with rare exception, should get a flu vaccine every season. For most people who need only one dose for the season, it says September and October are generally good times to be vaccinated, and that, ideally, everyone should be vaccinated by the end of October.

The CDC says flu vaccines cause antibodies to develop in the body about two weeks after vaccination.

## Sources

1. [Flu Season](https://www.cdc.gov/flu/about/season.html), Centers for Disease Control and Prevention, 2025-09-26 (primary source)
2. [Key Facts About Seasonal Flu Vaccine](https://www.cdc.gov/flu/vaccines/keyfacts.html), Centers for Disease Control and Prevention, 2026-09-01 (primary source)