The Centers for Disease Control and Prevention and the World Health Organization conduct surveillance throughout the world for novel or potentially pandemic forms of the influenza virus. The strain originally identified as the most likely to have pandemic potential was avian flu. In April 2009, H1N1, or swine flu, appeared in the human population and reached pandemic proportions.
Influenza
Every year, the influenza virus spreads around the world in epidemics. In the United States, about 36,000 people die yearly from flu-related causes. The most common types of influenza virus in humans are type A and B, which produce symptoms such as sore throat, cough, body aches and a fever of 100 degrees F or more. There are multiple subtypes of type A influenza, including avian flu and H1N1 flu, the CDC says.
Avian Flu
Avian flu is also known as bird flu, or subtype H5N1; it was first confirmed in the human population in 1997. This influenza virus occurs naturally in birds and poultry and has had limited, unsustained human-to-human spread so far. Most cases of avian flu have occurred in southeast Asian countries such as Indonesia, Vietnam and Thailand. The symptoms of avian flu are similar to those of seasonal flu, with complications that include severe breathing problems and pneumonia. According to the World Health Organization, avian flu has an unusually high mortality rate of 60 percent.
H1N1 Flu
H1N1 is commonly known as swine flu and is a new virus that entered the human population in 2009, leading to global transmission of the virus, known as a pandemic. The virus was first called swine flu because it was originally thought to have originated from a flu virus that occurs naturally in pigs in North America. Further study showed that the virus was actually composed of genes from a flu virus found in European and Asian pigs, avian genes and human genes. The symptoms of H1N1 are similar to those of seasonal flu and most people who have been infected with this virus recover without needing medical treatment.
Similarities
H1N1 and avian flu are both type A influenza viruses that have avian genetic components. Both of these strains are being monitored for pandemic potential--in the case of H1N1, it has already reached pandemic levels. These are both fairly new flu strains that are not commonly seen in the human population and have the potential to overload health care systems, the CDC says.
Differences
H1N1 has already reached pandemic levels, while avian flu has not achieved sustained human-to-human transmission. H1N1 began in North America and traveled around the globe, but avian flu has predominantly been limited to southeast Asia. While H1N1 has similar mortality rates to seasonal flu, avian flu has unusually high mortality rates and much higher instances of severe complications leading to death. The H1N1 vaccine was rapidly developed during the 2009 pandemic and distributed to the public. In 2007, a vaccine for avian flu was created, but is not available to the public and is housed in stockpiles in the event of a pandemic.
