Flu Vaccinations Facts. Service Areas. Differences between Pandemic influenza, seasonal flu and Avian Influenza. What flu strains are we expecting? Recommendations for the upcoming flu season. Aitor Aspiazu. Fast quote here! Last Name. Reason for your enquiry.
Onsite Flu Shots. Flu Vouchers. Phone We will only contact you when absolutely necessary. What can we do for you? I want to upload relevant information to help with my enquiry. Privacy Policy. Get a Quick Response. Please select if any of the below applies. I have or will have the Immunisation Course before March. Each sequence from a specific influenza virus has its own branch on the tree. The degree of genetic difference between viruses is represented by the length of the horizontal lines branches in the phylogenetic tree.
The further apart viruses are on the horizontal axis of a phylogenetic tree, the more genetically different the viruses are to one another. An influenza clade or group is a further subdivision of influenza viruses beyond subtypes or lineages based on the similarity of their HA gene sequences. See the Genome Sequencing and Genetic Characterization page for more information.
Clades and subclades are shown on phylogenetic trees as groups of viruses that usually have similar genetic changes i. Dividing viruses into clades and subclades allows flu experts to track the proportion of viruses from different clades in circulation. Note that clades and sub-clades that are genetically different from others are not necessarily antigenically different.
These proteins act as antigens. Antigens are molecular structures on the surface of viruses that are recognized by the immune system and can trigger an immune response such as antibody production. Therefore, for antigenically different viruses, immunity developed against one of the viruses will not necessarily protect against the other virus as well.
Influenza A H3N2 viruses also change both genetically and antigenically. Influenza A H3N2 viruses have formed many separate, genetically different clades in recent years that continue to co-circulate. Similar to influenza A viruses, influenza B viruses can then be further classified into specific clades and sub-clades.
Influenza B viruses generally change more slowly in terms of their genetic and antigenic properties than influenza A viruses, especially influenza A H3N2 viruses. Influenza surveillance data from recent years shows co-circulation of influenza B viruses from both lineages in the United States and around the world.
However, the proportion of influenza B viruses from each lineage that circulate can vary by geographic location and by season. Figure 2 — This image shows how influenza viruses are named.
The name starts with the virus type, followed by the place the virus was isolated, followed by the virus strain number often a sample identifier , the year isolated, and finally, the virus subtype. CDC follows an internationally accepted naming convention for influenza viruses. Public health officials will recommend that people practice everyday preventive actions at all times.
These actions include staying home when sick, covering coughs and sneezes with a tissue, washing hands often, and cleaning frequently touched surfaces and objects. During severe, very severe, or extreme flu pandemics, public health officials may recommend additional actions, such as using facemasks when sick and in close contact with other people, temporarily dismissing child care facilities and schools, and increasing the space between people and decreasing the frequency of contact among people that is, social distancing.
CDC has developed an updated set of guidelines, called the Community Mitigation Guidelines to Prevent Pandemic Influenza — United States, , supplemental plain-language guides for specific community groups, and online communication and education materials that outline strategies for planning and preparing for a flu pandemic and for using nonpharmaceutical interventions NPIs.
A novel influenza flu virus is an influenza A virus that has caused human infection and which is different from current human seasonal influenza A viruses. Any novel influenza A virus , such as those of avian or swine origin, has the potential to cause an influenza pandemic. Some novel flu A viruses are believed to pose a greater pandemic threat and are more concerning to public health officials than others because they have already caused serious human illness and death and also have been able to spread in a limited manner from person to person.
Novel influenza A viruses are of extra concern because of the potential impact they could have on public health if they gained the ability to spread from person-to-person easily and thus trigger an influenza pandemic.
Examples of novel influenza A viruses of extra concern because of their potential to cause a severe pandemic include avian influenza A H5N1 and avian influenza A H7N9 viruses. These two different avian influenza A viruses have caused sporadic human infections, some limited person to person spread and resulted in critical illness and death in people. Influenza viruses that normally circulate in pigs also have infected people ; these viruses include influenza A H1N1v , H1N2v and H3N2v.
Limited, unsustained spread from person to person also has been detected with these viruses, but in general, these variant viruses have been associated with less severe illness and fewer deaths than avian influenza viruses. In general, human infections with H5N1, H7N9, H1N1v, H1N2v and H3N2v viruses have occurred rarely, but if these viruses were to change in such a way that they were able to infect humans easily and spread from person to person in a sustained manner, a flu pandemic could result.
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