What's the difference between H1N1 flu and influenza A?
Answer From Pritish K. Tosh, M.D.
Flu (influenza) viruses are divided into four broad categories: influenza A, B, C or D. Influenza A is the most common type. H1N1 flu is a subtype of influenza A.
Subtypes of influenza A are categorized based on two proteins on the surface of the virus, hemagglutinin (H) and neuraminidase (N). There are many H and N subtypes, and each one is numbered. All H and N flu subtypes are influenza A viruses.
Each influenza subtype has many different strains of influenza virus. Not all strains infect people. Subtypes of influenza A viruses currently found in people are strains of H1N1 and H3N2. Each year's flu vaccine includes varieties of both of these strains and influenza B.
Pritish K. Tosh, M.D.
May 18, 2021
- Types of influenza viruses. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/about/viruses/types.htm. Accessed Aug. 15, 2019.
- Groshkopf LA, et al. Prevention and control of seasonal influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2018-2019 influenza season. MMWR Recommendations and Reports. 2018: doi:10.15585/mmwr.rr6703a1.
- Tosh PK (expert opinion). Mayo Clinic. Aug. 19, 2019.