What Is Swine Flu (H1N1)?

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Swine flu is the name for the influenza type A virus that affects pigs (swine). Although swine flu doesn't typically affect humans, there was a global outbreak in 2009 to 2010. This pandemic was the first such flu pandemic in more than 40 years.

It was caused by a then-new flu virus known as H1N1. With this, swine, avian (bird), and human flu strains mixed together in pigs and spread to humans.

H1N1 is now considered a normal type of seasonal flu. It is included in the annual flu vaccines.

This article explains the H1N1 virus and the symptoms you may experience with it. It discusses how this type of flu is diagnosed and treated, as well as the importance of getting your annual flu shot.

Verywell / Lara Antal


The Centers for Disease Control and Prevention (CDC) reported that H1N1 was first detected in April 2009 in two 10-year-olds, a boy and a girl living in California. The global pandemic was declared by the World Health Organization (WHO) in June 2009 and was over in August 2010.

The CDC estimates that swine flu infected nearly 61 million people in the United States and caused 12,469 deaths. Worldwide, up to 575,400 people died from pandemic swine flu.

The 1918 influenza pandemic also was caused by an H1N1 virus. Known as the Spanish flu, its genes showed that it may have evolved from a swine flu virus or from a bird flu virus. This pandemic killed an estimated 50 million people worldwide. It was notable in that it had a high death rate among healthy adults.

Today, H1N1 is just one of the seasonal flu types included in vaccines used to prevent influenza.


When H1N1 emerged in April 2009, it was a nove (new) virus for humans. This led to its rapid spread and a swine flu pandemic that claimed thousands of lives.

Swine Flu Symptoms

H1N1 causes respiratory illness and is very contagious. Symptoms of H1N1 are similar to those of the traditional seasonal flu. These symptoms may include:

  • Fever
  • Body aches
  • Loss of appetite
  • Cough
  • Sore throat
  • Headache
  • Fatigue
  • Runny nose
  • Irritated eyes
  • Vomiting, nausea
  • Diarrhea


Type A influenza viruses have the ability to mix with other strains. This creates a new strain, which is what happened to cause the most recent H1N1 pandemic.

Pigs are able to contract all three types of flu (human, swine, and avian). This makes them perfect vessels in which the virus can mix and change. The H1N1 virus was transformed in pigs, hence the "swine flu" name. This mixing likely happened a few years before the pandemic occurred.

Influenza circulates among pigs throughout the year but is most common during the late fall and winter. This is similar to the human flu season.

Sometimes pigs can pass the flu to farmers and other humans who work with them. This is what happened in 2009 to 2010. In this case, though, the new H1N1 strain spread quickly because humans had no immunity to it.

People get the H1N1 virus the same way they get any other type of flu. They make contact with another person who is sick, from either droplets in the air that contain the live virus or by touching a surface that has been contaminated. They then touch their eyes, nose, or mouth.

You can't get influenza from eating pork, though you should always make sure that it's cooked thoroughly and handled carefully.


You can get swine flu by breathing in infected droplets put into the air by someone who is sick or touching a surface that has these droplets.


If you develop signs of the flu and are otherwise in good health, you likely don't need to see a healthcare provider.

However, if you're pregnant or your immune system is compromised, you should see your provider right away. That's also the case if you have a chronic illness such as asthma, diabetes, emphysema, or a heart condition.

Your provider will be able to diagnose your flu by taking a swab from your nose and/or throat within the first four to five days of your sickness.

There are rapid influenza tests that can tell if you have the flu or not, as well as which type (A or B). They are not as accurate as other tests, though.

H1N1 Swine Flu Healthcare Provider Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

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Tests called rapid molecular assays are more accurate and can give a quick result. But since there is more than one strain of influenza A virus, a positive influenza A test doesn't necessarily mean it is the H1N1 virus.

To definitively diagnose and classify a strain of influenza, such as H1N1, your healthcare provider may send your samples to a specialized hospital or state lab for analysis.


If you are healthy and have a fever, sore throat, or other signs of the flu, you probably don't need medical attention. But people who have underlying medical issues, like diabetes, should contact their healthcare provider right away. Lab tests can confirm type A influenza.


H1N1 flu is a virus just like any other strain of flu. The antiviral medications Tamiflu and Relenza do not cure the illness, but they may make it shorter and the symptoms less severe. They also may help you avoid it altogether if you are exposed.

These medications are usually given to people who are at a higher risk of complications. This is because limiting their use overall may help keep the virus from developing a resistance to the drugs.

Treatment for most people usually means comfort care and treating symptoms as they occur. If you have asthma or emphysema, for instance, your healthcare provider might add a medication to help relieve your respiratory symptoms.

Annual flu shots now provide immunity against H1N1, meaning that swine flu has become a preventable illness.


The H1N1 caused a pandemic because it was a new kind of influenza type A virus. It is also called "swine flu" because it emerged in pigs as the virus evolved into H1N1 and then infected humans.

Today, it is treated as another influenza type A virus that can be prevented by getting your annual flu shot. The fever, body aches, and other symptoms common with the flu are the same.

Most people will not need to see a healthcare provider and H1N1 flu will run its course. Antiviral medications may help, but they are usually given to those at higher risk of complications.

A Word From Verywell

As with any type of flu, you should respect the H1N1 virus. But there's no reason to be afraid of it, even though complications can occur with any flu.

Getting your annual flu shot, washing your hands thoroughly and often, and staying away from infected people can help lower your risk of picking up any strain of flu.

Frequently Asked Questions

  • How many deaths were caused by swine flu in the U.S.?

    According to CDC estimates, between April 2009 to March 2010, swine flu caused a total of 12,469 deaths among all age groups in the U.S.

  • How long did the swine flu pandemic last?

    The WHO declared swine flu a global pandemic in June 2009 and determined it was over in August 2010. H1N1 swine flu still exists in today's population, but it no longer poses a major concern.

  • How is swine flu prevented?

    The annual flu vaccine protects against swine flu. Even with the vaccine, it's still a good idea to regularly wash your hands and stay away from infected people.

10 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.
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