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Swine flu

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

  • Human cases of swine influenza A (H1N1) virus infection were first identified in Mexico but cases are now being identified in other parts of the world including the UK:
    • cases have presented with symptoms of influenza-like illness
      • fever and respiratory tract illness, headache, muscle aches
      • some cases of swine influenza have presented with vomiting and diarrhoea
    • cases of severe respiratory disease, including deaths have been reported (1)
    • there is evidence of human-to-human transmission of swine flu (1)
    • the swine influenza virus is a novel influenza A virus
    • children and young adults appear to be most susceptible to clinical infection with the highest incidence in 5-9 and 10-14 year olds with a smaller number of cases in adults older than fifty years of age (born before 1957). The low number of cases seen in those aged over fifty is thought to be due to previous exposure in this age group to similar strains of H1N1 that circulated between 1918 and 1957 (2)
  • Management of swine influenza:
  • Post-exposure prophylaxis:
    • prophylaxis after contact with a case of pandemic flu needs to be considered in those at highest risk, many of whom will also have been targeted for vaccination
      • please refer to the detailed guidance document available from
      • prophylaxis with antivirals should be considered regardless of vaccination status, particularly in immunosuppressed individuals who may have a suboptimal response to vaccine
      • although post-exposure vaccination is unlikely to be effective within the time period required, consultation following a possible exposure does provide an opportunity to provide longer term protection in those who have not yet been fully vaccinated. Influenza A(H1N1)v vaccine should therefore be offered as soon as possible to anyone in a clinical risk group who has not yet been fully vaccinated.


  1. CDC interim guidance (30/4/09)
  2. Department of Health. The Green Book. Pandemic influenza A(H1N1)v 2009.

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