Cause virus h1n1

Few young people had any existing immunity as detected by antibody response to the H1N1 pdm09 virus, but nearly one-third of people over 60 years old had antibodies against this virus, likely from exposure to an older H1N1 virus earlier in their lives. Since the H1N1 pdm09 virus was very different from circulating H1N1 viruses, vaccination with seasonal flu vaccines offered little cross-protection against H1N1 pdm09 virus infection.

While a monovalent H1N1 pdm09 vaccine was produced, it was not available in large quantities until late November—after the peak of illness during the second wave had come and gone in the United States. Additionally, CDC estimated that ,, people worldwide died from H1N1 pdm09 virus infection during the first year the virus circulated.

This differs greatly from typical seasonal influenza epidemics, during which about 70 percent to 90 percent of deaths are estimated to occur in people 65 years and older. Though the flu pandemic primarily affected children and young and middle-aged adults, the impact of the H1N1 pdm09 virus on the global population during the first year was less severe than that of previous pandemics. Estimates of pandemic influenza mortality ranged from 0. It is estimated that 0.

However, H1N1 pdm09 virus continues to circulate as a seasonal flu virus, and cause illness, hospitalization, and deaths worldwide every year. Skip directly to site content Skip directly to page options Skip directly to A-Z link. Influenza Flu. Section Navigation. H1N1 is a type of influenza A virus, and H1N1 is one of several flu virus strains that can cause the seasonal flu. Symptoms of the H1N1 flu are the same as those of the seasonal flu.

In the spring of , scientists recognized a particular strain of flu virus known as H1N1. This virus is a combination of viruses from pigs, birds and humans that causes disease in humans. During the flu season, H1N1 caused the respiratory infection in humans that was commonly referred to as swine flu. In August , WHO declared the pandemic over. After the pandemic was over, the H1N1 flu virus became one of the strains that cause seasonal flu.

The flu vaccine can now help protect against the H1N1 flu swine flu. The H1N1 flu virus strain is included in the seasonal flu vaccine, including the vaccine for The signs and symptoms of flu caused by the H1N1 virus are similar to those of infections caused by other flu strains and can include:.

It's not necessary to see a doctor if you're generally healthy and develop flu signs and symptoms, such as fever, cough and body aches. Call your doctor, however, if you have flu symptoms and you're pregnant or you have a chronic disease, such as asthma, emphysema, diabetes or a heart condition, because you have a higher risk of flu complications.

If you have emergency signs and symptoms of the flu, get medical care right away. For adults, emergency signs and symptoms can include:. Influenza viruses such as H1N1 infect the cells that line your nose, throat and lungs.

The virus enters your body when you inhale contaminated droplets or transfer live virus from a contaminated surface to your eyes, nose or mouth. If you live in or travel to an area where many people are infected with the H1N1 virus, you may be exposed to the virus.

Each year's seasonal flu vaccine protects against the three or four influenza viruses that are expected to be the most common during that year's flu season. The flu vaccine can reduce your risk of the flu and its severity and lower the risk of having serious illness from the flu and needing to stay in the hospital. Flu vaccination is especially important in the flu season because the flu and coronavirus disease COVID cause similar symptoms.

Preventing the flu and reducing the severity of flu illness and hospitalizations could also lessen the number of people needing to stay in the hospital. The flu vaccine is available as an injection and as a nasal spray. The nasal spray is approved for use in healthy people ages 2 through 49 years old. The nasal spray isn't recommended for some groups, such as pregnant women, children between 2 and 4 years old with asthma or wheezing, and people who have compromised immune systems.

For example, you may need to practice social distancing physical distancing and stay at least 6 feet 2 meters from others outside your household. 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.

This convention was accepted by WHO in and published in February in the Bulletin of the World Health Organization, 58 4 see A revision of the system of nomenclature for influenza viruses: a WHO Memorandum pdf icon[ KB, 7 pages]external icon pdf icon external icon. The approach uses the following components:.

Getting a flu vaccine can protect against these viruses as well as additional flu viruses that are antigenically similar to the viruses used to make the vaccine.

Seasonal flu vaccines do not protect against influenza C or D viruses or against zoonotic animal-origin flu viruses that can cause human infections, such as variant or avian flu viruses.

In addition, flu vaccines will NOT protect against infection and illness caused by other viruses that also can cause influenza-like symptoms. There are many other viruses besides influenza that can result in influenza-like illness ILI that spread during flu season.

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