What is Swine Flu?

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Swine flu is a variant of influenza caused by the H1N1 virus. This virus strain caused a worldwide spread of infection from June 2009 to August 2010. The variant of the virus was termed 2009 H1N1 by the Centers for Disease Control and Prevention. Its technical name is the (H1N1)pdm09 virus.

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Where did swine flu originate?

The Swine flu infection first appeared in Mexico and spread worldwide rapidly, including to the UK.

Swine flu pandemic of 2009-2010

The World Health Organization declared a pandemic in June 2009. Surprisingly, the number of cases was high in summer, out of the flu season.

The numbers rose steadily until October before declining, and by February 2010, the pandemic had resulted in 15,921 deaths worldwide. On 10 August 2010, the World Health Organization declared that the swine flu pandemic was officially over. (2, 4, 5)

Where did the H1N1 virus come from?

The Swine flu virus is a type of influenza A. There are also influenza B and C types of viruses. (1, 2, 3)

H1N1 virus was initially found in pigs. With time the virus changed (mutated) and, in what is called a spillover event or spillover infection, infected humans.

In 2009 the novel variant spread quickly worldwide. Those between ages 5 and 24 years were the worst affected.

The infection returned in the 2010-2011 flu season; however, the H1N1 virus then did not cause widespread infections in 2009-2010.

A major reason for the weakening of the virus was that the 2010-2011 seasonal flu vaccine protected against swine flu, and a separate vaccine was not needed.

This holds true for 2011-2012 seasonal flu vaccine as well. (1, 3)

Why can swine flu spread so rapidly?

Swine flu spreads so rapidly and can achieve epidemic proportions because it can spread from person to person.

When a person with flu coughs or sneezes into the air that others breathe in or when someone leaves the virus on used articles like doorknobs, phones, computers, etc., or while taking care of a child or adult who is ill with the H1N1 flu virus.

Swine flu does not spread from eating pork or any other food, drinking water, saunas, or pools. (1)

Symptoms of swine flu

The symptoms of swine flu are similar to a typical case of influenza.

These symptoms include:

  • Fever
  • Headache
  • Body aches
  • Fatigue
  • Loss of appetite
  • Sneezing
  • Coughing

In addition, swine flu may also cause nausea, vomiting and diarrhea, chest congestion, and a sore throat. The symptoms are trivial and often resolve by themselves.

However, there is also a risk of more severe symptoms and of complications like pneumonia. About one percent of those affected are at high risk of death due to these complications.

Who is most at risk of complications?

Those at risk of complications are pregnant women, children, the elderly, and those with a suppressed immunity or with a permanent diseased condition such as chronic respiratory disease. (1, 2)

Recommendations for people in high-risk groups

It is recommended that people in these high-risk groups are vaccinated against swine flu. This includes all pregnant women at all pregnancy stages, those with chronic lung, heart, kidney, liver or neurological disease (e.g., Parkinson's disease), those who have suppressed immunity and diabetics.

Those with asthma and people aged over 65 are also at risk.


Further Reading

Last Updated: Feb 17, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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