H1N1 Flu

Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
The English language content on this website is being archived for historic and reference purposes only.
For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

Questions & Answers

2009 H1N1 Flu In The News

November 24, 2009 6:00 PM ET

Reports of Changes to the 2009 H1N1 Virus

Have changes to the 2009 H1N1 virus been reported?

The majority of 2009 H1N1 viruses tested by CDC and the other three World Health Organization (WHO) Collaborating Centers located around the world are similar and have changed relatively little since April 2009 when the 2009 H1N1 virus was first detected. However, there have been occasional reports of small changes in the genes of some virus samples collected from some people infected with 2009 H1N1 in several countries.

What are these changes to the 2009 H1N1 virus and what are the implications for public health?

The changes to the 2009 H1N1 virus that have been reported out of Norway, and that WHO has reported as being detected occasionally in viral isolates in other countries, are scientifically known as D222G and D222N changes. The public health implications of these changes are currently being studied by CDC and WHO scientists. At this time, these changes appear to occur sporadically and spontaneously. No links between the small number of patients infected with 2009 H1N1 virus with these changes have been found, and viruses with these changes do not appear to be spreading to other people. Although further investigation is underway, there is no evidence that these changes in the 2009 H1N1 virus have lead to an unusual increase in the number of 2009 H1N1 infections or to a greater number of severe or fatal cases. Worldwide, these changes have been found in mild cases of 2009 H1N1 illness as well as severe cases of illness that have resulted in death. As a result, the public health significance of this finding remains unclear.

Will the 2009 H1N1 vaccine still protect against these viruses?

According to CDC and WHO experts, the 2009 H1N1 vaccine remains well matched with the 2009 H1N1 viruses that contain these small changes. There is no reason to think that the 2009 H1N1 vaccine will be less effective against these viruses based on the area of the influenza virus where these changes have occurred.

Will antiviral drugs work against the 2009 H1N1 viruses that have these changes?

The D222G and D222N changes found in these 2009 H1N1 isolates are not associated with resistance to oseltamivir or any other influenza antiviral medication.

Which countries have reported finding 2009 H1N1 viruses with these changes?

A recent report from the Norwegian Institute of Public Health described a change in the 2009 H1N1 virus (D222G) found in the first two people in Norway who died from 2009 H1N1 as well as an additional Norwegian patient with severe influenza illness. This D222G change was not found in the virus samples isolated from other people who died in Norway of 2009 H1N1 related causes. Norwegian scientists have analyzed samples from more than 70 patients infected with 2009 H1N1, and no additional viral isolates containing these changes have been found.

In addition to Norway, CDC has received sporadic reports of these changes found in viral isolates from Australia, Brazil, China, Japan, Mexico, Saudi Arabia, Ukraine, Uruguay and the United States.