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Influenza vaccine

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The influenza vaccine is unusual among other vaccines because it must adapt to rapid virus evolution and therefore changes from year to year, authorised by the World Health Organisation.

Gravid med influensa
Illustrasjonsfoto: Colourbox.com

The influenza vaccine is unusual among other vaccines because it must adapt to rapid virus evolution and therefore changes from year to year, authorised by the World Health Organisation.


The seasonal influenza vaccine usually consists of three influenza viruses: one type A subtype H1N1 strain, one type A subtype H3N2 strain, and one type B strain. 

Composition of the seasonal vaccine

The World Health Organization (WHO) has established a network of national influenza centres that monitor influenza activity and recommend the composition of each season's vaccine.

Who is the influenza vaccine recommended for?

For some, influenza can be life-threatening. Most at risk are those who have reached a certain age or who have a chronic underlying disease or condition that means the body cannot tolerate influenza very well. If you are among these risk groups, the vaccine against seasonal influenza is recommended:

  • Pregnant women after week 12 of pregnancy (2nd and 3rd trimester). Pregnant women in 1st trimester which belongs to an additional risk group may be considered for vaccination.
  • Residents in nursing homes and sheltered accommodation
  • Everyone aged over 65
  • Children and adults with: 
    • diabetes mellitus, type 1 og 2 
    • chronic respiratory disease 
    • chronic cardiovascular disease 
    • chronic liver failure 
    • chronic renal failure 
    • chronic neurological disease or injury 
    • immunodeficiency disorders 
    • severe obesity (BMI over 40) 
    • other severe or chronic illness evaluated on an individual basis by a doctor

Other groups

In addition, the influenza vaccine is recommended to the following groups: 

  • Health professionals with patient contact. These are largely exposed to infection, and if they become infected, they can be a significant source of infection for their patients. 
  • Household contacts of immunosuppressed patients should consider vaccination against influenza to protect the patient.
  • Pig farmers and others who have regular contact with live pigs. The main reason to vaccinate pig farmers is to protect pigs against influenza infection, thus preventing the development of new viruses among pig herds. 

Why are pregnant women a risk group?

Most pregnant women who get influenza recover without complications and without damage to the foetus. Pregnant women have a slightly increased risk for influenza complications such as pneumonia, compared to other healthy. This risk seems to increase throughout the pregnancy. If the mother develops serious complications, the foetus is at risk. It has also been shown that influenza during pregnancy increases the risk of stillbirth.

Vaccination of the mother during pregnancy can protect the baby against influenza shortly after birth.

Why is the vaccine recommended to risk groups?

Almost 1 million people in Norway belong to groups at increased risk for complications of influenza. It is estimated that an average of 900 people die each year in Norway as a result of influenza. The influenza vaccine could save many of these lives.

Influenza can cause pneumonia and worsening of chronic underlying diseases. With severe complications from influenza, hospitalisation is often needed. Some people have permanently impaired health after severe influenza.

Influenza vaccination 

  • results in fewer hospital admissions  
  • reduces the risk of complications and permanently impaired health
  • saves lives

Side effects

Side effects from inactivated vaccines usually begin shortly after vaccination and rarely after two days. There is no evidence that the trivalent inactivated influenza vaccine can cause serious medical problems. 

  • Local reaction with redness, tenderness and/or swelling at the injection site (5 – 20 %)
  • Symptoms such as fever, muscle aches and general malaise (1 – 10 %)
  • Allergic reactions (hives, anaphylaxis) (extremely rare)

Protection

The full effect of vaccination is achieved within 2 weeks. In seasons with a good match between the viruses in the vaccine and the circulating viruses, the protection against laboratory-confirmed influenza is 50- 80 % among healthy adults aged under 65 years. 

Most studies show that the vaccine is less effective among the elderly than younger people. During the influenza season, the risk of complications, hospitalisation and death due to influenza are higher among the elderly and people with certain other diseases. Therefore, there is good reason to use the available vaccine against severe infection with admission to hospital and against death. 

Inactivated influenza vaccine is less effective among the youngest children and has not been tested among babies under 6 months.

Protection lasts for the influenza season. Long-term protection has not been studied but as the influenza virus is constantly evolving, a new vaccine dose is usually necessary every year.

Live influenza vaccine

In autumn 2013, a new influenza vaccine which is administered as a nasal spray became available in Norway. This live, attenuated influenza vaccine (LAIV) contains viruses that are cold-adapted and temperature sensitive so they cannot cause influenza illness. The vaccine is quadrivalent (two influenza A strains and two influenza B strains). LAIV should not be given to children younger than two years or older than 17 years of age. Since the vaccine contains live viruses, it should not be given to pregnant women or children or adolescents who are clinically immunodeficient. 

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