A brief history
Influenza has caused seasonal epidemics and occasional pandemics for centuries, including the 1918 pandemic. Influenza A virus was isolated in 1933, helping pave the way for vaccines. Changes in circulating viruses are one reason flu vaccination is updated for each season.
How does it spread?
Flu spreads through respiratory particles released by infected people, particularly during close contact. Contaminated hands can also carry the virus to the eyes, nose or mouth. A person may spread flu before recognising that they are ill.
Symptoms and possible complications
Flu often starts suddenly with fever, muscle aches, headache, cough and marked exhaustion. It can cause pneumonia or worsen existing heart and lung conditions. Older adults, young children, pregnant people and people with certain medical conditions are more likely to develop serious illness. Influenza is a different infection from the common cold.
Where it may be relevant
- Adults aged 18-49: we use Cell-based Trivalent Influenza Vaccine Seqirus, manufactured using cell cultures rather than eggs.
- Adults aged 50 and over: we use Adjuvanted Trivalent Influenza Vaccine Seqirus. Its MF59 adjuvant helps strengthen the immune response. This product is egg-grown.
- Both vaccines are made by Seqirus and target three seasonal influenza strains. Our age split describes the clinic service; the cell-based product has a wider licensed age range.
Dose schedules
The clinician will select the appropriate licensed schedule after reviewing age, health, previous doses and departure date.
Annual flu vaccination
Adults aged 18 and over
One 0.5 ml injection into the upper-arm muscle (intramuscular). Repeat each flu season.
Who may be eligible
- Adults aged 18 and over following a suitability assessment
- Adults seeking seasonal protection, including travellers
Who may not be eligible
- A serious allergy to a previous flu vaccination or a relevant ingredient requires review
- Vaccination is postponed during an illness with fever
- The adjuvanted product must not be used during pregnancy or breastfeeding; discuss a suitable alternative
Potential side effects
- A sore injection site, headache, tiredness and muscle aches are common with these vaccines
- Redness or swelling can occur; adjuvanted vaccine may also cause joint aches
- Severe allergic reactions require urgent treatment
Important risks and precautions
- Tell the clinician about allergies, previous vaccine reactions, bleeding problems and medicines that suppress immunity
- Vaccination does not protect everyone and protection can be weaker with immune suppression
- The cell-based vaccine can be used during pregnancy and breastfeeding following assessment
Clinical references