Overview

The H1N1 flu, commonly known as swine flu, is primarily caused by the H1N1 strain of the flu (influenza) virus. H1N1 is a type of influenza A virus, and H1N1 is one of several flu virus strains that can cause the seasonal flu. Symptoms of the H1N1 flu are the same as those of the seasonal flu.

In the spring of 2009, scientists recognized a particular strain of flu virus known as H1N1. This virus is a combination of viruses from pigs, birds and humans that causes disease in humans. During the 2009-10 flu season, H1N1 caused the respiratory infection in humans that was commonly referred to as swine flu. Because so many people around the world got sick, in 2009 the World Health Organization (WHO) declared the H1N1 flu to be a pandemic. In August 2010, WHO declared the pandemic over. After the pandemic was over, the H1N1 flu virus became one of the strains that cause seasonal flu.

The flu vaccine can now help protect against the H1N1 flu (swine flu). The H1N1 flu virus strain is included in the seasonal flu vaccine, including the vaccine for 2020-21.