Swine flu: The last pandemic declared by WHO before coronavirus, how does it compare?

The last time a pandemic was declared by the World Health Organisation was during the swine flu outbreak in 2009.

Also known as pig influenza, the virus is estimated to have killed as many as 575,000 people during the pandemic period.

"After early outbreaks in North America in April 2009 the new influenza virus spread rapidly around the world," the WHO said in 2011.

LIVE UPDATES: Australia unveils stimulus package

READ MORE: Coronavirus declared a pandemic by WHO

READ MORE: Everything you need to know about the coronavirus pandemic

By the time WHO declared a pandemic in June 2009, a total of 74 countries and territories had reported laboratory confirmed infections.

So far, more than 121,000 people have been infected worldwide and more than 4,300 have died from the current COVID-19 outbreak.

How did it start?

The swine flu was first recognised during the 1919 pandemic, but the H1N1 strain in the 2009 outbreak was first detected in humans in America.

Research found the virus was a "reassortment" of influenza viruses, where bird, swine and human flu viruses further combined with a Eurasian pig flu virus.

It is like a strain found in pigs in North America around 1999-2000.

Spread and symptoms

Like regular strains of influenza, swine flu is passed from person to person through exposure to infected droplets from coughing or sneezing, that can contaminate hands and surfaces.

Symptoms also mimic the flu, with patients experiencing fever, cough, headache, muscle and joint pain, sore throat and runny nose, and sometimes vomiting and diarrhoea.

Most people who were infected with swine flu during the pandemic suffered from mild cases of the illness and recovered without treatment.

There were a number of difficulties in counting the death toll of the swine flu, including differentiating it from other strains of influenza, and a lack of lab testing facilities in some regions.

When did it end?

By the end of 2009 two vaccines had been developed and administered in more than a dozen countries.

The first vaccine was similar to a regular flu shot and included an inactivated virus. The second was administered as a nasal spray and had a weak version of the virus that could not infect the recipient.

Both were produced by growing the virus inside chicken eggs.