Why H1N1 Is (and Isn't) Swine Flu

How the H1N1 Virus Became "Swine Flu"

H1N1 vaccine
Vials of H1N1 flu vaccine from the 2009 pandemic. Paul Kane/Getty Images News

The flu pandemic of 2009 seemed to appear out of nowhere in Mexico in April 2009. It quickly became known as "swine flu" because initial studies of the virus indicated there was a component that is found in common swine flu. Unfortunately for pigs and the pork industry, the name stuck even though it turned out that it’s not completely accurate.

So what is the pandemic flu if it’s not swine flu?

The novel pandemic H1N1 flu virus that caused the worldwide outbreak of illness is actually a combination of human, swine and bird influenza viruses.

It has genes from all three. So the term “swine flu” isn’t completely inaccurate, but it's not really correct either. 

Flu pandemic viruses develop when a strain of influenza mutates significantly, creating a virus that a majority of the human population has never been exposed to before. It most often occurs when a strain that affects another species - or multiple other species - mutate and develop the ability to make humans sick. 

The Swine Flu Myth

The use of the term “swine flu” has led to many misconceptions about this virus. It unnecessarily damaged the pork industry and led to the slaughter of thousands of pigs. This is one reason that officials have stopped calling the H1N1 virus “swine flu.”

Why the name H1N1?

All influenza viruses are classified as either type A, B or C. Type A influenza viruses are then put into subtypes where they have various H and N numbers assigned to them, depending on the proteins on the virus.

Scientists have identified 16 different “H” proteins and 9 different “N” proteins that occur on influenza A viruses. Influenza B and C do not have subtypes.

The flu virus that caused the flu pandemic of 2009 is an influenza A virus that has been categorized as H1N1. It is also believed that influenza A viruses caused the pandemics of 1918, 1957 and 1968.

Fortunately, the pandemic of 2009 did not turn out to be as severe as previous flu pandemics in the 20th century. There are other seasonal flu viruses that have the subtype of H1N1, but this one is different because it has genes from both avian and swine flu viruses, in addition to the genes that are typically found in seasonal human flu viruses. This is why it is referred to as the “novel” or pandemic H1N1 flu. 


”What’s the Difference Between Seasonal Flu, Pandemic Flu and Avian (Bird) Flu?” Flu (Influenza). National Institute of Allergy and Infectious Diseases. 14 Oct 08. US Department of Health and Human Services. 08 Sep 09.

”Why is this new H1N1 virus sometimes called “swine flu”?” Flu.gov. US Department of Health and Human Services. 08 Sep 09.

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