An acute viral infection of the respiratory tract. Influenza virus has 3 types: A, B, C. Strains responsible for clinical illness is A and B. It is highly infectious with an incubation period of 1 to 3 days. For healthy individuals, recovery is usually within 2 to 7 days but the illness may be complicated and may present as bronchitis, pneumonia, or in children, otitis media (ear infection) can occur.


Characterised by sudden onset of fever, chills, headache, body pain and fatigue that may be accompanied with sore throat, dry cough, and stuffy nose.


By droplets, aerosol, or through direct contact with respiratory secretions of someone with the infection. Influenza spreads rapidly, especially in closed communities.


The timing and extent of severity of “seasonal” influenza can all vary. Influenza A virus causes outbreaks most years and usually causes epidemic. Influenza B is less severe and causes smaller outbreaks. Most cases in the UK tend to occur during an eight- to ten-week period during the winter. Immunity from the previous virus may not protect completely against the new subtype, the population may have little or no immunity, and this may therefore lead to widespread epidemics or even a pandemic.


All Influenza vaccine in the UK are inactivated and do not contain live viruses except for Fluenz® Tetra which is administered via intranasal. None of the influenza vaccines can cause clinical influenza in those that can be vaccinated, although mild coryzal symptoms (acute inflammation of nasal cavities) can occur with the live vaccine. Each year, the viruses that are most likely to cause flu are identified in advance and vaccines are made to match them as closely as possible. Most injected flu jab protects against 3 types of flu virus. The WHO recommended that quadrivalent vaccines for 2021 to 2022 flu season contain the following:

  • an A/Victoria/2570/2019 (H1N1)pdm09-like virus;
  • an A/Cambodia/e0826360/2020 (H3N2)-like virus;
  • a B/Washington/02/2019 (B/Victoria lineage)-like virus; and
  • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus

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Vaccine Name Course Per Dose
Influenza 1 Dose £35