What is swine flu?

By Dr Ananya Mandal, MD

Swine flu is influenza caused by the H1N1 virus.

This virus strain is a new one that caused a worldwide spread of infection from June 2009 to August 2010.

The variant of the virus is now termed 2009 H1N1 by the Centers for Disease Control and Prevention.

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

Where did swine flu originate?

The Swine flu infection first appeared in Mexico.

This spread rapidly worldwide including 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 that was not the flu season at all.

The numbers rose steadily until October before declining.

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?

H1N1 virus initially was found in pigs.

With time the virus changed (mutated) and infected humans.

In 2009 the variant was a new one and it spread quickly worldwide. Those between ages 5 and 24 years were the worst affected.

The infection returned in 2010-2011 flu season however H1N1 virus then did not cause widespread infections as it had 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 air that others breathe in or when someone leaves the virus on used articles like door knobs, 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 usual case of influenza.

There may be fever, headache, body aches, fatigue, loss of appetite, sneezing and 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 per cent of those affected are likely to die due to these complications.

Who is most at risk of complications?

Those at risk of complications are pregnant women, children and the elderly as well as 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 stages of pregnancy, those with chronic lung, heart, kidney, liver or neurological disease (e.g. Parkinsonism) disease, those who have suppressed immunity and diabetics.

Those with asthma and people aged over 65 are also at risk. (5)

Edited by , BA Hons (Cantab)

Further Reading

Swine flu Causes
Swine flu Symptoms
Swine flu Diagnosis
Swine flu Treatments

Last Updated: Jun 26, 2012

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