H1N1 is a highly contagious respiratory disease. The first human case in the U.S. was detected in April 2009. The virus spreads from person-to-person, in the same way that regular seasonal influenza viruses spread. By June 19, 2009, all 50 states in the United States, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands reported cases of H1N1 infection.

The H1N1 flu virus was originally referred to as “swine flu” because initial laboratory tests showed that many of the genes in H1N1 virus were very similar to the influenza viruses that normally occur in pigs (swine) in North America. But further study has proven that H1N1 is very different from what normally circulates in North American pigs. H1N1 flu is NOT caused by eating pork or pork products.


2009 H1N1 flu symptoms include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. Some people may have vomiting and diarrhea. People may be infected with H1N1 and have respiratory symptoms without a fever. Severe illnesses and death has occurred as a result of illness associated with this virus.

How does 2009 H1N1 flu compare to seasonal flu in terms of its severity and infection rates?

Unlike the seasonal flu virus, adults older than 64 do not yet appear to be at increased risk of H1N1 flu-related complications. CDC laboratory studies have shown that about one-third of adults older than 60 may have antibodies against this virus. It is unknown how much protection may be afforded against H1N1 flu by an existing antibody.

Since flu-like symptoms can be a result of any strand of the flu, lab tests are the only way to confirm H1N1.


Vaccines offer the best protection. A vaccine for H1N1 became available for the public in the Fall 2009. The vaccine is manufactured in two forms, a nasal spray and a injectable form. As always, a vaccine will be available to protect against seasonal influenza. Throughout the flu season, the CDC continues to post updates on the vaccine, distribution and production as it becomes available.


Antiviral medications can reduce the severity and duration of influenza illness and can reduce the risk of influenza-related complications, including severe illness and death. There are four influenza antiviral drugs approved for use in the US. Laboratory tests have shown that only two, Oseltamivir (TAMIFLU®) and Zanamivir (RELENZA®) are effective in treating the H1N1 virus.


For the General Public

For Public Health Professionals