Seasonal influenza Influenza, or 'the flu', is a viral infection of the nose, throat and lungs (the respiratory system). Subtypes are named by combining the H and N numbers – e.g., A(H1N1), A(H3N2). Current subtypes of influenza A viruses that routinely circulate in people include: A(H1N1) and A(H3N2). Infections have occurred as a result of contact with infected birds. Influenza viruses are categorized as types A, B, C, and D. These major types generally produce similar symptoms but are completely unrelated antigenically, so that infection with one type confers no immunity against the others. (See the Note that clades and sub-clades that are genetically different from others are not necessarily antigenically different (i.e., viruses from a specific clade or sub-clade may not have changes that impact host immunity in comparison to other clades or sub-clades).Currently circulating influenza A(H1N1) viruses are related to the pandemic 2009 H1N1 virus that emerged in the spring of 2009 and caused a flu pandemic (Of all the influenza viruses that routinely circulate and cause illness in people, influenza A(H3N2) viruses tend to change more rapidly, both genetically and antigenically. However, during periods of low influenza activity and outside of epidemics situations, the infection of other respiratory viruses e.g. Comparisons among multiple vaccines aid understanding of current issues related to influenza vaccines and also offer insight into potential strategies to improve vaccine effectiveness. Influenza A viruses are the only influenza viruses known to cause flu pandemics, i.e., global epidemics of flu disease. A number of inactivated influenza vaccines and recombinant influenza vaccines are available in injectable form. Learn about types of flu viruses (including bird flu), the symptoms, and complications in high-risk groups. Influenza B viruses generally change more slowly in terms of their genetic and antigenic properties than influenza A viruses, especially influenza A(H3N2) viruses. Two types of influenza vaccine are widely available: inactivated influenza vaccines (IIV) and live attenuated influenza vaccines (LAIV). Thompson WW, Weintraub E, Dhankhar P, Cheng OY, Brammer L, Meltzer MI, et al. The pathogen. Influenza — also known as the flu — is a contagious viral infection that attacks your respiratory system. Various guidance on the laboratory techniques is published and updated by WHO. Saving Lives, Protecting People In a phylogenetic tree, related viruses are grouped together on branches. Learn more about flu and HIV/AIDS and find out how to prevent serious problems.If you have a chronic condition like heart disease, diabetes, or obesity, you need to take extra care to protect yourself from all types of the flu, but especially the strain pH1N1 (swine flu).If you're pregnant, be proactive about swine flu. Do you know the warning signs of flu, and how flu is different from a cold?

While wild birds are commonly immune to the devastating and possibly deadly effects of H5N1, the virus has killed more than half of the people infected with it. But he or she may want to give you a quick test to be sure the influenza virus is to blame, and not another health problem.People typically recover from flu after a week or two without any lasting problems. There are 18 different HA subtypes and 11 different NA subtypes. Types of influenza. The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year. Influenza A viruses are divided into subtypes on the basis of two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA).