What Is Swine Flu (H1N1)?

Table of Contents
View All
Table of Contents

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 (pandemic) in 2009 to 2010—the first flu pandemic in more than 40 years. It was caused by a then-new flu virus known as H1N1, an influenza virus that's a combination of swine, avian (bird), and human genes that mixed together in pigs and spread to humans. H1N1 is now considered a normal type of seasonal flu and is included in the flu vaccine.

Verywell / Lara Antal


H1N1 was first detected in April 2009 in a 10-year-old girl in California. It was declared a global pandemic in June 2009 by the World Health Organization (WHO) and was finally over in August 2010.

The Centers for Disease Control and Prevention (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 was also caused by an H1N1 virus. Known as the Spanish flu, its genes show that it may have developed from a swine flu virus or from an avian (bird) flu virus. The pandemic killed an estimated 50 million people worldwide and was notable in that it had a high death rate among healthy adults.

Swine Flu Symptoms

H1N1 causes respiratory illness and is very contagious. Symptoms of H1N1 are similar to those of the seasonal flu and 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, creating a new strain, which is what happened to cause the pandemic of 2009 to 2010.

Pigs are able to contract all three types of influenza (human, swine, and avian), make them perfect vessels in which the virus can mix and change. The H1N1 virus is made of swine, human, and avian genes that metamorphosed in pigs, probably several years before the pandemic (hence the name "swine flu.")

Influenza circulates among pigs throughout the year but is most common during the late fall and winter, similar to the human flu season. Sometimes pigs can pass the flu to the humans who work. This is what happened during the 2009 to 2010 pandemic, only, in this case, the new H1N1 strain spread quickly because humans had no immunity to it.

When people get the H1N1 virus, it's in the same way they can get any type of flu— by 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 and then touching your 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.


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, your immune system is compromised, or you have a chronic illness such as asthma, diabetes, emphysema, or a heart condition, you should see your practitioner right away.

Your medical professional will be able to diagnose you with the 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 diagnostic tests that can tell if you have the flu or not, as well as which type (A or B), though they are not as accurate as other tests.

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.

Doctor Discussion Guide Man

There are also rapid molecular assays, which are more accurate and can also give a rapid result. Since there is more than one strain of influenza A virus strain, a positive influenza A test doesn't necessarily mean you have the H1N1 virus. To definitively diagnose and classify the strain of influenza you have, such as H1N1, your healthcare provider may send your specimen to a specialized hospital or state lab for analysis.


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 shorten the duration, make symptoms less severe, or help you avoid it altogether if you are exposed. They are usually reserved for people who are at a higher risk of complications, so the likelihood of the virus developing a resistance to them is lessened.

Otherwise, treatment for most people mainly consists of comfort measures 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 preventable.

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. Though complications can occur as a result of getting any type of flu, getting your annual flu vaccine (which protects against H1N1), washing your hands regularly and thoroughly, and staying away from infected people can help lessen your risk of picking up any strain of flu.

Frequently Asked Questions

  • How many deaths were caused by swine flu in the US?

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

  • How is swine flu prevented?

    Receiving 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 people infected with the flu.

Was this page helpful?
Article 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.
  1. Jilani T, Siddiqui A. H1N1 influenza (swine flu). StatPearls. Updated December 14, 2019.

  2. Centers for Disease Control and Prevention. CDC Estimates of 2009 H1N1 Influenza Cases, Hospitalizations and Deaths in the United States.

  3. Dawood F, Iuliano A, Reed C et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling studyThe Lancet Infectious Diseases. 2012;12(9):687-695. doi:10.1016/s1473-3099(12)70121-4

  4. Jordan D. The deadliest flu: The complete story of the discovery and reconstruction of the 1918 pandemic virus. Centers for Disease Control and Prevention. Updated December 17, 2019.

  5. Centers for Disease Control and Prevention. 2009 H1N1 flu (“swine flu”) and you. 2010.

  6. Richard M, Fouchier RA. Influenza A virus transmission via respiratory aerosols or droplets as it relates to pandemic potential. FEMS Microbiol Rev. 2016;40(1):68-85. doi:10.1093/femsre/fuv039

  7. Allard R, Leclerc P, Tremblay C, Tannenbaum TN. Diabetes and the severity of pandemic influenza A (H1N1) infection. Diabetes Care. 2010;33(7):1491-3. doi:10.2337/dc09-2215

  8. Kim DK, Poudel B. Tools to detect influenza virus. Yonsei Med J. 2013;54(3):560-6. doi:10.3349/ymj.2013.54.3.560

  9. Dotis J, Roilides E. H1N1 influenza A infection. Hippokratia. 2009;13(3):135–138.

  10. Obuchi M, Adachi Y, Takizawa T, Sata T. Influenza A(H1N1)pdm09 virus and asthma. Front Microbiol. 2013;4:307. doi:10.3389/fmicb.2013.00307

Additional Reading