Influenza Vaccine
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The influenza vaccine is an annual vaccine, typically offered to patients at high risk of seasonal influenza (flu). It is not usually a live vaccine. Modern vaccines typically contain constituents of 4 strains of influenza. The exact strains included in vaccine formulations is decided up based on the previous years strains, and emerging strains noted around the globe.

Typically the vaccine is about 50-60% effective – meaning that of the people who receive the vaccine, the chances of contracting the flu in any given year are halved. This varies from year to year depending on the exact strains circulating and in the vaccine. It is thought that a small amount of immunity is conferred for subsequent years.

Efficacy is typically greatest in the first 3 months, and then starts to wane. In some very high risk groups (e.g. cancer patients), a second dose may be advisable later in the flu season. For most people this isn’t required.

It is typically recommended for everyone aged over 6 months, although in most developed countries, it is only “free” (government funded) for certain high risk groups. Other individuals may choose to pay for the own vaccine, and many employers choose to offer the vaccine to their workers to reduce the number of sick days over the winter.

Patients aged over 65 should received a ‘high dose’ vaccine, as in this age group, the immune response is less effective and a stronger dose is required to induce immunity.

There are several preparations available, and the exact brands and specifications change from year to year. There is a nasal spray variation available int he UK which is typically the type given to children.

H1N1 influenza virus
H1N1 influenza virus

Who should be vaccinated?

High risk groups are generally defined as:

  • Anyone aged over 65
  • Pregnant women – the vaccine can be given at any time during pregnancy
  • Anyone aged >6 months with a chronic illness – e.g. COPD, asthma, cardiovascular disease, diabetes, cancer, hepatitis B or C, HIV or any other long-term illness requiring ongoing medical care
  • Health care or social care workers
  • Those caring for a vulnerable relative at home
  • Children (NHS recommends primary school aged children, Australia recommends all children aged 6 months to 5 years)
  • In Australia – patients of Aboriginal or Torres Straight Islander background aged >15


  • Anaphylaxis to previous influenza vaccine or component of influenza vaccine * (see egg below – special case)
  • First episode of Guillain-Barre Syndrome within 6 weeks of an influenza vaccine
  • Currently febrile / unwell

Immunosuppressants are not a contra-indication

  • Taking specific immuno-oncological agents may be a contra-indication. These are; Ipilimumab, Nivolumab, Pemrolizumab – some sources suggest patients should NOT receive the HIGH DOSE (>65 versions) of the flu vaccine, but that the normal dose may not cause adverse effects. I would discuss with specialist (oncologist +/- infectious diseases) before giving the vaccine to anyone taking these drugs

Egg allergy

  • Allergy, including anaphylaxis is no-longer a true contraindication
  • Those with previous allergy to egg can safely be given full dose
  • Those with previous anaphylaxis to egg can be safely given full dose – but recommended to be given in an environment where they can be safely monitored and treated for anaphylaxis

Questions to ask the patient

  1. Have you ever received a flu vaccine before?
  2. Have you ever experienced any problems after receiving a flu vaccine in the past?
  3. Are you allergic to eggs or egg products?
  4. Have you had any severe allergies in the past?
  5. Do you have a fever or are you currently unwell?
  6. Do you have a history of Guillain-Barre Syndrome?
  7. What medications are you currently taking?

Potential side effects

  • Soreness at injection site – typically lasts for several days
  • Fever / flu like symptoms (malaise, myalgias)– usually for <48 hours
  • Doesn’t guarantee protection fro the flu – estimated efficacy is 50-60% in those aged <65


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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