What Is Swine Flu

  • Farah Hamdan M.Sc. in Infection Biology, M.Sc. in Clinical Laboratory, B.S. in Pharmacy and Pharmaceutical Chemistry, Tishreen University

Swine flu (swine influenza) is a respiratory illness of pigs that is caused by an influenza virus. In 2009, a new type of this virus, which was able to infect humans and be transmitted from person-to-person, appeared and caused a global pandemic which lead to thousands of deaths.  In this article, you will learn about swine flu, the virus that causes it,  signs and symptoms, treatment, diagnosis, and ways of prevention.

What is swine flu

Swine flu (swine influenza) is an infectious disease caused by a type of influenza virus. As the name suggests swine fluaffects pigs, and operates by attacking their respiratory system, causing huge economic losses in the swine industry.1 A new type of the virus that was able to infect humans caused a pandemic when it first appeared in 2009. The new virus was named H1N1 (2009), and it spread from person-to-person through respiratory droplets when coughing and sneezing, and when touching the nose or mouth after touching objects contaminated with the virus.1

Influenza viruses

There are four main types of influenza viruses named A, B, C, and D that can infect a wide range of hosts (e.g. humans, pigs, birds, etc.). While influenza C viruses cause mild disease and are not known to cause epidemics (sudden increase of disease cases in a specific area), and influenza D viruses infect cattle and not humans, influenza A and B types cause seasonal flu epidemics each year. Type A viruses are known to cause pandemics (a pandemic is declared by the World Health Organisation (WHO) when an infectious disease spreads rapidly to many countries and populations).

The virus that causes swine flu is an influenza A virus, and these viruses are classified according to two different proteins that are found on their surface, hemagglutinin (H) and neuraminidase (N). There are 11 different types of the N protein (N1-11) and 18 different types of the H protein (H1-18) and depending on what two types of these proteins the virus has, it gets its name, which explains the (H1N1) part of the swine flu’s virus name.1

The 2009 pandemic

The first case of the H1N1 (2009) virus appeared in Mexico in February of 2009, then in the United States in March of the same year, and soon spread to many countries including the UK. In June of 2009 the WHO declared a global pandemic, and people of younger age and pregnant women were the most affected; it was estimated that over 300,000 people died during that period.2

Signs and symptoms of swine flu

The incubation period (the time between being infected with the virus and the time the signs and symptoms appear) of swine flu ranges between 1-4 days and could be up to 7 days in some cases. If you are infected you can start infecting others one day before the signs and symptoms appear and up to 5 to 7 days afterwards.3

Most cases are mild with symptoms like that of the seasonal flu (CDC):

  • Fever
  • Myalgia (muscle pain)
  • Cough
  • Tiredness
  • Sore throat
  • Watery eyes
  • Runny nose
  • Nausea
  • Vomiting
  • Diarrhoea


  • Viral pneumonia (lung infection)
  • Bacterial pneumonia
  • Hemorrhagic bronchitis (inflammation in the respiratory airways with bloody sputum)

These complications can develop within two days of the appearance of symptoms and could be fatal in some cases. Some groups have a higher risk of developing serious illness:

  • Children under the age of five and young adults
  • People older than 65 years
  • Pregnant women
  • People with weak immune systems (due to illnesses like AIDS)
  • People with chronic diseases (e.g. diabetes, asthma, heart disease, etc.)3

Swine flu diagnosis

Your doctor might suspect that you have swine flu if you presented with flu-like symptoms and you lived in an area where the illness spread. To diagnose, your healthcare provider will order a respiratory sample, such as a throat or nose swab to detect the virus. A technique called RT-PCR, that detects the virus’s genetic material, is widely used for diagnosis.4

Swine flu treatment

Most cases are mild and will not require medication. If you are diagnosed with swine flu, you should:

  • Rest at home
  • Drink plenty of water and fluids
  • Inform family, friends, and neighbours to limit unnecessary visits

Medication you can take:

  • Painkillers to relieve fever and headache (e.g. acetaminophen or ibuprofen)But be aware of giving children aspirin, as in giving aspirin to children while having, or shortly after, a viral infection can lead to Reye’s syndrome, which is a life-threatening syndrome that causes swelling in the brain and damage to the liver.
  • Antivirals that are used to treat flu (e.g. oseltamivir, zanamivir, peramivir, baloxavir).However, the prescription of these drugs is preserved to people with higher risk of developing complications and people in close contact with them.4

Prevention of swine flu

There are several steps you can take to protect yourself from infection:

  • Washing your hands with water and soup regularly for 15-20 seconds
  • Avoid touching your face and nose with your hands
  • Avoid contact with people who are ill (CDC)
  • Vaccination:

There are several available vaccines for swine flu. People who are prioritised for vaccination are: regnant women at any stage of pregnancy, people whose immune system is affected by a disease or by certain medications, people who are in close contact to people at high risk.

Swine flu vaccines are safe and effective. However, they can cause mild short-term side effects such as headache, muscle aches, and fever. Some of the vaccines might not be suitable for people who are allergic to eggs. Therefore, you should seek advice from your healthcare provider in case you have allergies to egg products (NHS).


Should I isolate myself if I am diagnosed with swine flu?

Five days of isolation is recommended.3 You will become infectious (able to spread the illness to others) as soon as you develop symptoms and up to five days (7 days in children). Once the symptoms are gone, you are no longer infectious (NHS).

What can I do to prevent the spread of the virus to others if I am diagnosed with swine flu?

To protect others from being ill, you should:

  • Avoid contact with people, especially high-risk people (children under 5, people over 65, pregnant women, and people with chronic illnesses)
  • Cover your mouth with tissues when you cough and sneeze, and through the tissues as soon as you are done
  • Make sure that other people around you wash their hands with soap and water regularly (NHS)

Can I become ill from consuming well-cooked pork?

No, swine flu is not known to be transmitted by eating pork or other food products of pig sources. However, it is advisable to follow good hygienic practices when handling pork:

  • Always buy pork from trusted, licensed sources
  • Do not touch raw pork with your hands when buying
  • Do not touch your face after handling pork, and wash your hands with warm water and soap
  • Use detergent and water to clean all surfaces and equipment that were in touch with pork
  • Store pork separately in the fridge/freezer in closed containers
  • Before being consumed, pork must be thoroughly cooked so the centre parts reach at least 75 °C

For more details about good hygienic practices when handling pork products read HERE.

Can seasonal flu vaccines protect against swine flu?

No, if there is a need, the swine flu vaccine should be taken, and some people who are advised to take the seasonal flu vaccine might be advised to take the swine flu vaccine as well (NHS).


   Swine flu is a respiratory infection that is caused by type A influenza virus that affects pigs and has a global prevalence. A new variant of the virus, now known as (H1N1 (2009) flu), was able to infect humans, be transmitted from person-to-person, and caused a pandemic in 2009. Now, the virus is one of the causes of seasonal flu and causes mild illness that does not require antiviral treatment in most cases. Nonetheless, older people, pregnant women, and people with chronic diseases and weak immunity have a high risk of developing complications that can lead to death. Maintaining good hygiene practices, avoiding ill people, and vaccines can help prevent the infection. 


  • Ma W. Swine influenza virus: Current status and challenge. Virus Res. 2020 Oct 15;288:198118. doi: 10.1016/j.virusres.2020.198118. Epub 2020 Aug 13. 
  • Fineberg HV. Pandemic preparedness and response--lessons from the H1N1 influenza of 2009. N Engl J Med. 2014 Apr 3;370(14):1335-42.. 
  • Jilani TN, Jamil RT, Siddiqui AH. H1N1 Influenza. [Updated 2022 Oct 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513241/
  • Rewar S, Mirdha D, Rewar P. Treatment and Prevention of Pandemic H1N1 Influenza. Ann Glob Health. 2015 Sep-Oct;81(5):645-53. 
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Farah Hamdan

M.Sc. in Infection Biology, M.Sc. in Clinical Laboratory, B.S. in Pharmacy and Pharmaceutical Chemistry, Tishreen University

I am interested in infectious diseases and in studying the microorganisms causing them. I have years of experience teaching university students different health-related topics, and now, I aspire to transfer this knowledge to the public in a simple, clear way.

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