What Is Influenza?

By kyle
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Every year up to 11% of the American population is infected with influenza (flu). This respiratory illness comes in many different strains and can be highly contagious. Many cases are mild, but some severe cases result in death. There are many factors that can increase the risk of a fatal infection, as well as a number of prevention strategies to reduce your risk.

Find out more about the different strains of the flu, how it spreads, prevention strategies and why the flu vaccine is recommended to reduce the risk of an annual flu infection. Explore the common symptoms to determine whether you need to see a doctor for your flu-like symptoms.

1. What Are the Different Types of Influenza?

There are four main types of influenza, with many different subtypes. The four types are: A, B, C and D. Only influenza A and B are known to cause seasonal epidemics. Influenza C rarely affects humans and typically causes mild cases, while influenza D primarily infects cattle.

Each main type is then further classified into subtypes and given an H and N number such as H1N1 or H3N2. The infection rate, severity and other factors vary depending on the subtype of the flu. Understanding subtypes is critical to developing a vaccine and preventing further serious cases.


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