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Influenza A (H1N1) vaccination

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

  • prior to the swine flu pandemic, vaccine manufacturers had developed and tested new types of influenza vaccines that could be adapted when a pandemic arose. These monovalent (i.e. single strain) vaccines were developed with antigen from H5N1 influenza viruses - a virus to which most people have no immunity
    • influenza A(H1N1)v vaccines are, therefore, the same as these H5N1 vaccines except that the virus antigen comes from the WHO pandemic declared strain A/California/07/2009
  • there are two influenza A(H1N1)v vaccine products available for use in the UK
    • Pandemrix®, manufactured by GlaxoSmithKline, is a split virion, inactivated, adjuvanted vaccine. It is a monovalent vaccine containing 3.75 micrograms of antigen. The antigen used is A/California/07/2009 (H1N1)v-like strain (X-179A), propagated in fertilised hens�' eggs
      • vaccine contains an adjuvant (AS03) to help boost the immune response
    • Celvapan ®, manufactured by Baxter Healthcare, is a whole virion, inactivated, vero cell derived vaccine containing 7.5 micrograms of antigen
      • the antigen used is the wild-type A/California/07/2009 H1N1 strain
      • the whole virion is inactivated both by formaldehyde and UV-irradiation
      • does not contain an adjuvant
    • both vaccines are inactivated, do not contain live viruses and cannot cause flu
    • pregnant women
      • pregnant women should be offered Pandemrix® in preference to Celvapan®
        • this is because a one-dose schedule of Pandemrix® gives adequate levels of antibodies and thereby confers more rapid protection than would be afforded by the two-dose Celvapan® schedule at a time when pandemic influenza viruses are circulating
    • Clinical risk groups who should receive the influenza immunisation

Clinical risk category

Examples (decision based on clinical judgement)

Chronic respiratory disease, asthma

chronic obstructive pulmonary disease (COPD) including chronic bronchitis and emphysema; bronchiectasis, cystic fibrosis, interstitial lung fibrosis, pneumoconiosis and bronchopulmonary dysplasia (BPD).

Asthma that requires continuous or repeated use of inhaled or systemic steroids or with previous exacerbations requiring hospital admission.

Children who have previously been admitted to hospital for lower respiratory tract disease

Chronic heart disease

Congenital heart disease, hypertension with cardiac complications, chronic heart failure, individuals requiring regular medication and/or follow-up for ischaemic heart disease

Chronic renal disease

Chronic renal failure, nephrotic syndrome, renal transplantation

Chronic liver disease

Cirrhosis, biliary atresia, chronic hepatitis

Chronic neurological disease

Stroke, transient ischaemic attack (TIA).

Diabetes requiring insulin or oral hypoglycaemic drugs

Type 1 diabetes, type 2 diabetes requiring oral hypoglycaemic drugs, and diet controlled diabetes.


Immunosuppression due to disease or treatment. Patients undergoing chemotherapy leading to immunosuppression. Asplenia or splenic dysfunction. HIV infection at all stages. Individuals treated with or likely to be treated with systemic steroids for more than a month at a dose equivalent to prednisolone at 20mg or more per day (any age) or for children under 20kg a dose of 1mg or more per kg per day

  • Notes:
    • some immunocompromised patients may have a suboptimal immunological response to the vaccine
    • the examples within each group are not meant to be an exhaustive and exclusive list. It is not possible to list all conditions likely to be at higher risk. Healthcare practitioners should also use clinical judgement and take into account the risk of influenza infection exacerbating any underlying disease that a patient may have, as well as the risk of serious illness from influenza itself
    • The groups have been prioritised for vaccination in the following order:
      • i. Individuals aged six months and up to 65 years in the clinical at-risk groups (see Table above )
      • ii. All pregnant women
      • iii. Household contacts of immunocompromised individuals
      • iv.Individuals aged 65 years and over in the clinical at-risk groups (see Table above)
    • frontline health and social care workers should also receive the influenza A(H1N1)v vaccine as they are at increased risk of exposure to the virus and increased risk of transmitting the virus to vulnerable patients and to others including their own family members. Frontline staff are those who have regular clinical contact with patients and who are directly involved in patient care

For more detailed guidance then consult the Pandemic influenza A (H1N1) chapter in the Green Book (1).


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