Which animal does the flu come from?

Influenza viruses have been found in pigs, bats, chickens, horses, whales, and cats. Dogs can also get a version of the flu. Different flu strains are found in different animals. Some of these viruses can't be spread from animals to humans. Others, like " swine flu ," did make the jump from animals (pigs) to humans.

Can you get the flu all year round?

Influenza viruses are always around. While you're more likely to get sick when the viruses are at peak activity (e.g., during a flu season), you could get the flu at any time. If you have a weak immune system, you might be more likely to get the flu outside of flu season.

Why do we get the flu in the winter?

During the colder months of the year, people tend to spend more time inside in close quarters with others. This makes it easier for viruses, including the flu, to spread. The cold, dry weather also changes our nasal passages, making an environment that's much more hospitable to the flu virus.

Where does the flu go in the summer?

Flu viruses don't actually go away in the "off-season." While they're going around more during flu season, they're always in the environment.

Is sunlight good for protection against the flu?

In 2018, a group of researchers proposed that areas with more sunlight might have had lower influenza rates. While there are many health benefits of getting sunshine, more research is needed to understand if sunlight offers protection against the flu.

When is flu season over?

In the U.S., flu cases usually start to wane around April, and flu season is over by May.

When Is Flu Season?

The Exact Timing Can Vary

By Vincent Iannelli, MD

Updated on January 24, 2023

Medically reviewed by Rochelle Collins, DO

When flu season starts and ends depends on where you live. If you are in the United States, flu season usually starts in the fall.

Although flu season in the U.S. is usually in the winter, the severity and timing of a flu season vary from year to year.

This article will go over when flu season occurs in different parts of the world. You'll also learn which months the flu is active and when flu season is over.

When Is Flu Season? — Verywell / Lara Antal

When Exactly Is Flu Season?

In the U.S., flu season typically starts in October and peaks between December and February.

On average, flu season lasts about 13 weeks. It usually ends in April, but in some years, it goes into May.

When Should I Get a Flu Shot?

To protect yourself from influenza, the Centers for Disease Control and Prevention (CDC) recommends getting your yearly flu shot during September or October.

It is a good idea to get a flu shot before the start of flu season to avoid getting sick with the flu. Even a late flu shot provides protection, especially when a flu season lingers into April or May.

A Look at Past Flu Seasons

The strain of the flu that circulates can change from year to year. The flu vaccine is adjusted to try to predict which strain will predominate during the coming flu season.

Here is a look at the flu seasons over the last 10 years.

Season	Peak Month	Most Common Flu Strain
2019-2020	February	A(H1N1)pdm09
2018-2019	February	A(H1N1)pdm09; A(H3N2)
2017-2018	January and February	A(H3N2)
2016-2017	March	A(H3N2)
2015-2016	March	A(H1N1)
2014-2015	December	A(H3N2)
2013-2014	December	A(H1N1)pdm09
2012-2013	December	A(H3N2)
2011-2012	March	A(H3N2)
2010-2011	February	A(H3N2)

Summary

The months that the flu is going around depends on where you live. In the U.S., flu season usually starts in the fall and lasts until spring. Flu season in the U.S. usually peaks in January and February and ends by April or May.

The CDC recommends that everyone over the age of 6 months old gets a yearly flu vaccine. Try to get your flu shot as soon as it becomes available—by the end of October, if possible.

It takes about two weeks after getting vaccinated for your body to produce the antibodies that will protect you during flu season. If you missed the earlier vaccination time, it is still valuable to get the vaccine—even in January or later.

Frequently Asked Questions

Which animal does the flu come from?

Influenza viruses have been found in pigs, bats, chickens, horses, whales, and cats. Dogs can also get a version of the flu.
Different flu strains are found in different animals. Some of these viruses can't be spread from animals to humans. Others, like "swine flu," did make the jump from animals (pigs) to humans.
Can you get the flu all year round?

Influenza viruses are always around. While you're more likely to get sick when the viruses are at peak activity (e.g., during a flu season), you could get the flu at any time. If you have a weak immune system, you might be more likely to get the flu outside of flu season.
Why do we get the flu in the winter?

During the colder months of the year, people tend to spend more time inside in close quarters with others. This makes it easier for viruses, including the flu, to spread. The cold, dry weather also changes our nasal passages, making an environment that's much more hospitable to the flu virus.
Where does the flu go in the summer?

Flu viruses don't actually go away in the "off-season." While they're going around more during flu season, they're always in the environment.

Learn More: Can You Get the Flu in the Summer?
Is sunlight good for protection against the flu?

In 2018, a group of researchers proposed that areas with more sunlight might have had lower influenza rates. While there are many health benefits of getting sunshine, more research is needed to understand if sunlight offers protection against the flu.
When is flu season over?

In the U.S., flu cases usually start to wane around April, and flu season is over by May.

6 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Centers for Disease Control and Prevention. Flu season.
Grohskopf LA, Blanton LH, Ferdinands JM, et al. Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 influenza season. MMWR Recomm Rep. 2022;71(1):1-28. doi:10.15585/mmwr.rr7101a1
Centers for Disease Prevention and Control. Past flu seasons.
Centers for Disease Control and Prevention. Influenza in Animals.
Ference RS, Leonard JA, Stupak HD. Physiologic model for seasonal patterns in flu transmission. Laryngoscope. 2020;130(2):309-313. doi:10.1002/lary.27910
Slusky DJG, Zeckhauser RJ. Sunlight and protection against influenza. Econ Hum Biol. 2021;40:100942. doi:10.1016/j.ehb.2020.100942

Additional Reading

CDC. Past Weekly Surveillance Reports.

By Vincent Iannelli, MD
Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.

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