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Influenza

Understanding Influenza

Influenza is a viral infection of the respiratory tract and is highly infectious. Symptoms include sudden onset of fever, chills, muscle pain, fatigue, headache, dry cough, sore throat and stuffy nose. Most healthy individuals usually recover within two to seven days, however complications can occur which may present as bronchitis, pneumonia or, less commonly, meningitis. 

The risk of serious illness from influenza is higher amongst children under six months of age, older people and those with underlying health conditions such as heart or lung conditions, chronic health conditions such as liver or kidney diseases, diabetes or immunosuppression and pregnant women.

There are several different types of vaccines for protection against influenza, the vaccines are prepared using virus strains in line with the World Health Organisation (WHO) recommendations.  The current recommendation for flu vaccination are:

Children aged 2-17 years

  • The live attenuated influenza vaccine (LAIV) (unless medically contraindicated). LAIV is given by nasal spray as it contains live viruses that have been weakened and adapted to cold so that they can only replicate at the lower temperatures found in the nasal passage. These live viruses cannot replicate efficiently elsewhere in the body but may cause mild symptoms such as runny nose or headache. All the other flu vaccines in the UK are inactivated and cannot cause clinical influenza in those that are vaccinated.
     
  • For children aged 6 months to under 2 years, as well as those over 2 who are unable to have the live vaccine, the inactivated vaccine can be given by injection rather than nasal spray. 

For those aged 18 to 64 years, there are two vaccines which are suitable.

  • The standard influenza vaccine (egg-grown quadrivalent -four strains of influenza virus vaccine).  
  • A newly licenced cell-based quadrivalent influenza vaccine. 

Previously the influenza vaccine has been manufactured by culturing it in eggs, which lets the virus adapt to grow in the egg, and this can lead to changes to the virus in the manufacturing process. 

Through cell culture technology this egg-adaptation does not occur, the influenza virus grows well in the cells and it is able to produce high volumes of flu virus for use in vaccines.  Both vaccines offer protection against four strains of flu. 

If an individual has had an allergy to eggs, having the flu vaccination should be discussed with the doctor or nurse. Anyone with a severe anaphylaxis to egg should not have the egg-grown vaccine vaccine, but those with less severe allergies can normally be immunised after discussion with medical practitioner.

For those aged 65 and over, there are three vaccines that are available.

  • The adjuvanted trivalent influenza vaccine, which has three strains and an adjuvant. An adjuvant is an ingredient added to a vaccine that helps create a stronger immune response.   
  • The newly licenced cell-based quadrivalent influenza vaccine. 
  • The newly licenced high dose trivalent influenza, which is not readily available.

All pregnant women should be offered an inactivated quadrivalent influenza vaccine whilst pregnant, regardless of their stage of pregnancy. 

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