As an expert in the field of epidemiology and infectious diseases, with a focus on influenza viruses, I have a deep understanding of the various types and classifications of these pathogens. Influenza, commonly known as the flu, is a highly contagious respiratory illness caused by influenza viruses. These viruses are classified into four types: A, B, C, and D, with A, B, and C being the types that commonly infect humans.

The H1N1 influenza you're referring to is a subtype of the influenza A virus. It is important to note that influenza A viruses are further categorized into different subtypes based on two surface proteins: hemagglutinin (H) and neuraminidase (N). The "H" stands for the number of hemagglutinin subtypes, and the "N" stands for the number of neuraminidase subtypes. The H1N1 designation specifically refers to a virus that has type 1 hemagglutinin and type 1 neuraminidase.

The 2009 H1N1 pandemic was caused by a novel strain of the H1N1 influenza A virus. This virus was unique because it resulted from a reassortment of genetic material from different influenza viruses, including human, avian, and swine strains. The pandemic marked the first time in more than 40 years that a new strain of influenza A had emerged to cause a global outbreak.

In contrast, influenza B viruses are not divided into subtypes like influenza A. However, they are classified into two distinct lineages: B/Victoria/2/87-like and B/Yamagata/16/88-like. These lineages are further divided into strains based on genetic and antigenic differences. Influenza B viruses generally cause milder illness compared to influenza A and are less likely to cause pandemics, but they still pose a significant health risk, particularly to young children, the elderly, and individuals with weakened immune systems.

It is crucial to understand the differences between these types of influenza viruses because it influences how we approach vaccination, treatment, and public health strategies. The World Health Organization (WHO) monitors the circulating strains of influenza globally and provides recommendations for the composition of the annual influenza vaccine to ensure it targets the most prevalent strains.

Vaccination remains one of the most effective ways to prevent influenza and its complications. The flu vaccine is designed to protect against the influenza A (H1N1) virus, an influenza A (H3N2) virus, and either one or two strains of influenza B, depending on the vaccine formulation.

In summary, H1N1 influenza is a subtype of the influenza A virus, not type B. The 2009 H1N1 pandemic highlighted the importance of surveillance, preparedness, and the need for a robust public health response to emerging infectious diseases. Understanding the characteristics and differences between influenza A and B viruses is vital for the development of effective vaccines and antiviral treatments to protect public health.

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The new virus caused the first influenza pandemic in more than 40 years. That virus (often called --2009 H1N1--) has now replaced the H1N1 virus that was previously circulating in humans. Influenza B viruses are not divided into subtypes, but can be further broken down into lineages and strains.Sep 27, 2017read more >>