Influenza A (H1N1), Influenza A (H3N2), and one or two influenza B viruses (depending on the vaccine) are included in each year’s influenza vaccine now.
How Influenza even got started to now:
Influenza was discovered not by a direct study of the disease in humans, but rather from studies on animal diseases. In 1918, J.S. Koen, a veterinarian, observed a disease in pigs which was believed to be the same disease as the now famous “Spanish” influenza pandemic of 1918.
In the 20th century, three influenza pandemics occurred: Spanish influenza in 1918 (~50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths). The World Health Organization declared an outbreak of a new type of influenza A/H1N1 to be a pandemic in June 2009. Influenza may also affect other wild life which are horses, chickens and birds along with the pigs. In late 1917, military pathologists reported the onset of a new disease with high mortality that they later recognized as the flu. The overcrowded camp and hospital — which treated thousands of victims of chemical attacks and other casualties of war — was an ideal site for the spreading of a respiratory virus; 100,000 soldiers were in transit every day. It also was home to a live piggery, and poultry were regularly brought in for food supplies from surrounding villages. Oxford and his team postulated that a significant precursor virus, harbored in birds, mutated so it could migrate to pigs that were kept near the front.
Influenza A virus subtype H5N1, also known as A(H5N1) or simply H5N1, is a subtype of the influenza A virus which can cause illness in humans and many other animal species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza (“bird flu“). It is enzootic (maintained in the population) in many bird populations, especially in Southeast Asia.
CDC Centers for Disease Control blog site states, “There are four types of influenza viruses: A, B, C and D. Human influenza A and B viruses cause seasonal epidemics of disease almost every winter in the United States. The emergence of a new and very different influenza A virus to infect people can cause an influenza pandemic. Influenza type C infections generally cause a mild respiratory illness and are not thought to cause epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.
Influenza A viruses can be further broken down into different strains. Current subtypes of influenza A viruses found in people are influenza A (H1N1) and influenza A (H3N2) viruses. In the spring of 2009, a new influenza A (H1N1) virus (CDC 2009 H1N1 Flu website) emerged to cause illness in people. This virus was very different from the human influenza A (H1N1) viruses circulating at that time. 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. Currently circulating influenza B viruses belong to one of two lineages: B/Yamagata and B/Victoria. Unlike type A flu viruses, type B flu is found only in humans. Type B flu may cause a less severe reaction than type A flu virus, but occasionally, type B flu can still be extremely harmful. Influenza type B viruses are not classified by subtype. However, influenza B viruses do not cause pandemics.
CDC follows an internationally accepted naming convention for influenza viruses. This convention was accepted by WHO in 1979 and published in February 1980 in the Bulletin of the World Health Organization, 58(4):585-591 (1980) (see A revision of the system of nomenclature for influenza viruses: a WHO Memorandum[854 KB, 7 pages]). The approach uses the following components:
- The antigenic type (e.g., A, B, C)
- The host of origin (e.g., swine, equine, chicken, etc. For human-origin viruses, no host of origin designation is given.)
- Geographical origin (e.g., Denver, Taiwan, etc.)
- Strain number (e.g., 15, 7, etc.)
- Year of isolation (e.g., 57, 2009, etc.)
- For influenza A viruses, the hemagglutinin and neuraminidase antigen description in parentheses (e.g., (H1N1), (H5N1)
For example:
- A/duck/Alberta/35/76 (H1N1) for a virus from duck origin
- A/Perth/16/2009 (H3N2) for a virus from human origin
Getting a flu vaccine can protect against flu viruses that are the same or related to the viruses in the vaccine. Information about this season’s vaccine can be found at Preventing Seasonal Flu with Vaccination. The seasonal flu vaccine does not protect against influenza C viruses. Additionally, flu vaccines will NOT protect against infection and illness caused by other viruses that also can cause influenza-like symptoms. There are many other non-flu viruses that can result in influenza-like illness (ILI) that spread during flu season. If people got vaccines high odds there would be less influenza spreading throughout the country you live in or globally with travelers for both pleasure and business.
- Flu vaccines have been updated to better match circulating viruses [the B/Victoria component was changed and the influenza A(H3N2) component was updated].
- For the 2018-2019 season, the nasal spray flu vaccine (live attenuated influenza vaccine or “LAIV”) is again a recommended option for influenza vaccination of persons for whom it is otherwise appropriate. The nasal spray is approved for use in non-pregnant individuals, 2 to 49 years old. There is a precaution against the use of LAIV for people with certain underlying medical conditions. All LAIV will be quadrivalent (four-component).”
PMC U.S. National Library of Medicine (National Institutes of Health) states, “the announcement in 2005 that a virus causing fatal influenza during the great influenza pandemic of 1918–1919 had been sequenced in its entirety [1], in the laboratory of co-author JKT, has prompted renewed interest in the 1918 virus. The ongoing H5N1 avian influenza epizootic, and the possibility that it might also cause a pandemic [2], increase the importance of understanding what happened in 1918. However, in reviewing the scientific approach to unlocking an old puzzle, it is important to note that the sequencing of the 1918 virus took place after more than century of exhaustive and sometimes disheartening efforts to discover the cause of influenza (Figure 1). Indeed, the influenza search not only pre-dated the great pandemic of 1918, but also attracted the efforts of some of the greatest researchers of the 19th and 20th centuries. Along the way, the new fields of bacteriology and virology were advanced, and a productive marriage between microbiology, epidemiology and experimental science began. In describing here the 10-year effort (1995–2005) to sequence the genome of the 1918 pandemic influenza virus, we attempt also to place it within this important historical perspective.”
Influenza virus C is a genus in the virus family Orthomyxoviridae, which includes the viruses that cause influenza. Nearly all adults have been infected with influenza C virus, which causes mild upper respiratory infections. Cold-like symptoms are associated with the virus including fever (38-40ᵒC=100.4 to 104F), dry cough, rhinorrhea (nasal discharge), headache, muscle pain, and achiness. The virus may lead to more severe infections such as bronchitis and pneumonia. Lower tract complications are rare. There is no vaccine against influenza C virus.
The species in this genus is called Influenza C virus. Influenza C viruses are known to infect humans and pigs.
Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.