Influenzavirus

The influenza virus is an RNA virus from the orthomyxovirus family (Orthomyxoviridae). The virus is divided into 3 types A, B and C on the basis of the two antigens nucleoprotein (NP) and matrix antigen (M) located inside the virus. Types A and B are morphologically similar.

Influenza virus A (highest pathogenicity for humans)

• Influenza virus A variant (H1N1) - causative agent of the Spanish flu (1918)
• Influenza virus A variant (H1N1) - causative agent of swine flu (2009)
• Influenza virus A variant (H2N2) - causative agent of Asian flu (1957)
• Influenza virus A variant (H3N2) - pathogen of the Hong Kong flu (2009)
• (avian) influenza virus A variant (H5N1), highly pathogenic avian influenza virus (HPAIV), increasingly pathogenic for humans.
• (avian) influenza virus A variant (H7N2), low pathogenic avian influenza virus (LPAIV)
• (avian) influenza virus A variant (H7N3), low pathogenic avian influenza virus (LPAIV)
• (avian) influenza virus A variant (H7N7), highly pathogenic avian influenza virus (HPAIV)
• (avian) influenza virus A variant (H9N2), low pathogenic avian influenza virus (LPAIV)

Influenzavirus B (clinically indistinguishable from influenza virus A)

Influenza virus C (rare occurrence)

A further classification of the influenza A virus is based on the glycoproteins incorporated in the viral envelope:

- haemagglutinin (H)

and

- neuraminidase (N).

Hemagglutinin (H) is rod-shaped and enables attachment to the host cells.

Neuraminidase (N) has the form of a fungus and causes the release of the viruses from the infected cells and also their spread in the respiratory tract.

There are now 18 known H subtypes and 9 N subtypes. However, only 6 H-types (H1, H2, H3, H5, H7, H9) and 3 N-subtypes (N1, N2, N7) have been detected in human epidemics to date. However, other subtypes can occur at any time.

Influenza viruses cause influenza, an acute respiratory disease with pronounced systemic symptoms. Pneumonia can develop as a complication, which can be fatal, especially in older people with chronic underlying illnesses. Type A viruses cause periodic global epidemics (pandemics), while species A and B cause recurring local epidemics.

Vaccination: The active vaccination against influenza contains a tri- or tetravalent inactivated vaccine (2 A strains plus 1-2 B strains. The vaccination must be repeated annually, as the vaccine is adapted to the WHO recommendations so that the antigen composition corresponds to the current epidemic strains.

The protection rate of the vaccination is approx. 60% in patients < 65 years of age; the protection rate is lower in older people. The mortality rate in people > 60 years of age can be demonstrably reduced by vaccination. However, exact figures on this vary widely in the literature. There is also evidence that the vaccination reduces cardiovascular mortality (apoplexy, myocardial infarction).

The nasal attenuated vaccine available for children and adolescents from 2 to 18 years of age is not effective against A/H1N1 viruses.

Sufficient protection for the patient is provided approximately 14 days after vaccination.

Previously, it was said that the vaccine's active ingredient only lasts for 3-4 months and that people should therefore not be vaccinated too early. November was recommended as the optimal time, as the peak of the disease typically falls around the beginning of February. In the meantime, manufacturers have stated that the vaccine is effective for 6 - 12 months.

Indications for vaccination:

• - generally all persons > 60 years of age
• - Persons with congenital, acquired or drug-induced weakening of the immune system
• - Persons with cardiopulmonary diseases
• - pregnant women
• - Persons with increased exposure
• - Persons exposed to direct contact with birds and/or wild birds (no protection against avian infection, but against double infection)
• - in the event of epidemics, ALL patients should be vaccinated

Contraindications for vaccination:

• - Patients who are acutely ill with a febrile infection
• - Persons with protein allergy (a chicken protein-free vaccine is available here)

Side effects of the vaccination:

Occasionally, mild general reactions occur, such as

• - Pressure pain at the injection site
• - Chicken protein allergy (rare)
• - Vasculitis (very rare)
• - Thrombocytopenia (very rare)
• - Guillain-Barré syndrome (1:1 million)
• - Narcolepsy after vaccination against swine flu (very rare)

The influenza virus is an RNA virus of the orthomyxovirus family. Based on the two antigens nucleoprotein (NP) and matrix antigen (M) located inside the virus, the virus is divided into the 3 types A, B and C. The types A and B are morphologically similar.

The Influenza A virus is classified as influenza A virus because of the glycoproteins:

- haemagglutinin (H) and

- neuraminidase (N) into further subtypes.

Haemagglutinin (H) is rod-shaped and enables attachment to the host cells.

The neuraminidase (N) has the shape of a fungus and causes the release of the viruses from the infected cells and also their spread in the respiratory tract.

In the meantime, 18 H-subtypes and 9 N-subtypes are known. However, so far only 6 H-types (H1, H2, H3, H5, H7, H9) and 3 N-subtypes (N1, N2, N7) have been detected in human epidemics. However, other subtypes can occur at any time.

The designation of new subtypes depends on

- Type

- first site

- sequential number

- Year

- Antigen formula (H or N)

Example: Influenza A/ California/7/2009(H1N1)

Influenza A and influenza B are widespread worldwide, while influenza C only occurs sporadically.

Route of transmission: Transmission occurs by droplet infection and also by smear infection. However, there must be a high virus titer in the nasopharyngeal secretion.

Nomenclature: The designation of new subtypes is based on:

• - type
• - first locality
• - serial number
• - year
• - Antigen formula (H or N)
• Example: Influenza A/ California/7/2009(H1N1)

Obligation to report: According to § 7 of the Infection Protection Act (IfSG), there is a nationwide obligation to report influenza viruses by name to the laboratory if they are directly detected.

In Saxony, according to the Ordinance on the Extension of the Obligation to Report Communicable Diseases and Pathogens under the Infection Protection Act § 1, doctors are also obliged to report both the illness and death from influenza by name.

Important: After an influenza vaccination, the HIV test can be false positive for up to 3 weeks!

1. Herold et al. (2017) Internal Medicine p 875-877
2. Infection Protection Act (IfSG) of the Federal Ministry § 7 Reportable evidence of pathogens.
3. Köhler et al. (2010) Pneumology 54: 90
4. Li YT et al. (2019) Avian influenza viruses in humans: lessons from past outbreaks. Br Med Bull 132: 81-95.
5. Loscalzo J et al (2011) Harrison's pulmonary medicine and intensive care p 163-175.
6. LVWA Saxony Additional reporting obligation according to the ordinance on the extended reporting obligation for communicable diseases.