Influenza A(H1N2) Viruses
Questions and Answers
The new 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 based on 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 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.
It is unknown where the A(H1N2) virus originated, but on February 6, 2002 the World Health Organization (WHO) and the Public Health Laboratory Service (PHLS) in the United Kingdom reported the recent identification influenza A(H1N2) viruses from humans in England, Israel, and Egypt. In addition to the viruses reported by PHLS, the Centers for Disease Control and Prevention and the Wisconsin Division of Public Health have identified an influenza A(H1N2) virus from a patient specimen collected during December 2001 in Wisconsin. Although this is the first time in recent years that A(H1N2) viruses have been identified, they have circulated transiently in the past. Between December 1988 and March 1989, 19 influenza A(H1N2) viruses were identified in 6 cities in China, but the virus did not spread further.
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 donít 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.
No. A pandemic virus has to have a new hemagglutinin or a new hemagglutinin and neuraminidase protein that has not circulated in 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 these viruses and have antibodies against those viruses.
There is no information to suggest that the A(H1N2) viruses are causing a more severe illness than other influenza viruses and no unusual increases in influenza activity have been associated with this virus. The pattern of illness seen with the H1N2 viruses 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 school age children, but do not frequently effect the elderly.
Yes. Because both the H and N protein on the A(H1N2) virus closely match the H and N proteins included in the current influenza vaccine, the vaccine should provide good protection against influenza A(H1N2) viruses as well protection against as the currently circulating A(H1N1), A(H3N2), and B viruses.