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Questions and Answers About Influenza A(H1N2) Viruses
NOTE: This document is provided for historical purposes only and may not reflect the most accurate and up-to-date information on this subject. For current flu information, please visit the CDC Flu Homepage.
On this page:
- What is influenza A(H1N2) virus?
- Where did the A(H1N2) virus come from and where has it been identified?
- How is this virus different from other currently circulating influenza A viruses?
- Is this the start of a pandemic?
- Does the A(H1N2) virus cause more severe illness than other influenza viruses?
- Will the influenza vaccine I received for the 2003-04 influenza season protect me from A(H1N2) viruses?
1) What is influenza A(H1N2) virus?
The new A(H1N2) strain appears to have resulted from the reassortment of the genes of the currently circulating influenza A(H1N1) and A(H3N2) subtypes. Influenza viruses can be divided into two types, influenza type A viruses and influenza type B viruses. Influenza A viruses can be further divided into subtypes on the basis of two proteins, hemagglutinin (H) and neuraminidase (N), found on the surface of the virus. Since 1977, two influenza A subtypes, A(H1N1) and A(H3N2), have circulated widely among people. The hemagglutinin protein of the A(H1N2) virus is similar to that of the currently circulating A(H1N1) viruses and the neuraminidase protein is similar to that of the current A(H3N2) viruses.
2) Where did the A(H1N2) virus come from and where has it been identified?
It is unknown where the A(H1N2) virus originated, but on February 6, 2002, the World Health Organization (WHO) in Geneva and the Public Health Laboratory Service (PHLS) in the United Kingdom reported the identification influenza A(H1N2) virus from humans in England, Israel, and Egypt. In addition to the virus isolates reported by WHO and PHLS, the Centers for Disease Control and Prevention has identified influenza A(H1N2) virus from patient specimens collected during the 2001-02 and 2002-03 seasons. Influenza A(H1N2) viruses have circulated transiently in the past. Between December 1988 and March 1989, 19 influenza A(H1N2) virus isolates were identified in 6 cities in China, but the virus did not spread further.
3) How is this virus different from other currently circulating influenza A viruses?
The H1N2 virus is not very different from the currently circulating influenza viruses. The H1 protein of the H1N2 virus is like the H1 protein of the currently circulating H1N1 viruses and the N2 protein is similar to the N2 protein in the currently circulating H3N2 viruses. The difference is that we don't commonly see the H1 and N2 proteins on the same virus. There has been no unusual increase in disease associated with this virus, and persons infected with the virus are expected to have influenza illness typical of A(H1N1) viruses.
4) Is this the start of a pandemic?
No. A pandemic virus has to have a new hemagglutinin or a new hemagglutinin and neuraminidase protein on an influenza A virus that has not circulated among humans and to which most or all of the population has no protective antibodies. Because the H1N2 virus has the hemagglutinin of the currently circulating H1N1 virus and the neuraminidase of the currently circulating H3N2 virus, most people will have been exposed to and have antibodies against these viruses.
5) Does the A(H1N2) virus cause more severe illness than other influenza viruses?
There is no information to suggest that the A(H1N2) virus is causing a more severe illness than other influenza viruses, and no unusual increases in influenza activity have been associated with the A(H1N2) virus. The pattern of illness seen with the A(H1N2) virus is expected to be similar to disease caused by A(H1N1) viruses. Influenza A(H1N1) viruses are seen more commonly among younger persons and can be associated with outbreaks among children, but do not frequently affect the elderly.
6) Will the influenza vaccine I received for the 2003-04 influenza season protect me from A(H1N2) viruses?
Yes. Because both the hemagglutinin and neuraminidase protein on the A(H1N2) virus closely matches the hemagglutinin and neuraminidase proteins of viruses included in the current influenza vaccine, the vaccine should provide good protection against influenza A(H1N2) virus as well as protection against the currently circulating A(H1N1), A(H3N2), and B viruses.
Other Links:
- Content Source: Coordinating Center for Infectious Diseases (CCID)
- National Center for Immunization and Respiratory Diseases (NCIRD)
