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Winter doesn’t just mean colder temperatures – there is also a rise in some diseases, including the number of cases of flu.

The word flu is short for influenza, which is a fairly common disease. Symptoms include fever, cough, runny nose and muscle aches. Those affected can often be sick for a week or more. The flu is caused by the influenza family of viruses. There isn’t just one type of flu – there are many strains.

Experts believe the disease is spread by people with flu coughing and sneezing, which releases droplets including virus particles. Coming into contact with these droplets can lead to infection. After infection with one strain, most people will develop immunity but only to that group of viruses. Influenza viruses mutate and change, rapidly creating new strains.

While most people will recover from a case of the flu, it can be fatal. Flu pandemics occur when a new flu strain spreads easily and quickly. For example, the Spanish influenza pandemic in 1918–1919 is estimated to have killed about 50 million people – more than World War I that preceded it.

Humans aren’t the only animals affected by influenza. In recent years there have been prominent cases of bird flu and swine flu. They attracted attention because they started in animals, before spreading to humans. The swine flu strain H1N1 caused the most recent influenza pandemic in 2009–2010, which is estimated to have killed about 200 000 people.

The most effective method of preventing flu is through vaccination. In Australia, the flu vaccine typically contains three inactivated strains of influenza virus. The vaccine triggers an immune response and the body produces antibodies. If a person is then infected with one of the groups of influenza virus covered by the vaccine, these antibodies will recognise the virus and fight it.

Influenza viruses are constantly changing, so it’s necessary to receive the vaccine every year. A flu vaccine doesn’t cover all strains, so it’s still possible to catch the flu even after receiving the vaccine. However, the strains included in the vaccine are selected to maximise protection in a particular flu season.

There are other, simple ways to help prevent the spread of flu. Cover your mouth when you cough or sneeze, wash your hands frequently and stay home in bed when you’re sick to help stop the spread!