Oseltamivir, amantadine (review) and zanamivir for the prophylaxis of influenza

Oseltamivir and zanamivir are recommended, within their marketing authorisations, for the post-exposure prophylaxis of influenza if all of the following circumstances apply.

• National surveillance schemes have indicated that influenza virus is circulating. The Health Protection Agency in England (and the equivalent bodies in Wales and Northern Ireland) uses information from a range of clinical, virological and epidemiological influenza surveillance schemes to identify periods when there is a substantial likelihood that people presenting with an influenza-like illness are infected with influenza virus.

• The person is in an at-risk group as defined in section 1.3.

• The person has been exposed (as defined in section 1.4) to an influenza-like illness and is able to begin prophylaxis within the timescale specified in the marketing authorisations of the individual drugs (within 36 hours of contact with an index case for zanamivir and within 48 hours of contact with an index case for oseltamivir).

• The person has not been effectively protected by vaccination (as defined in section 1.5).

The choice of either oseltamivir or zanamivir in the circumstances described in section 1.1 should be determined by the healthcare professional in consultation with patients and carers. The decision should take into account preferences regarding the delivery of the drug and potential adverse effects and contraindications. If all other considerations are equal, the drug with the lower acquisition cost should be used.

For the purpose of this guidance, people at risk are defined as those who fall into one or more of the clinical risk groups defined, and updated, each year by the Chief Medical Officer. The current list includes people with:

• chronic respiratory disease (including asthma that requires continuous or repeated use of inhaled or systemic steroids or with previous exacerbations requiring hospital admission)

• chronic heart disease

• chronic renal disease

• chronic liver disease

• chronic neurological disease

• immunosuppression

• diabetes mellitus.
  
  People who are aged 65 years or older are also defined as at-risk for the purpose of this guidance.

Exposure to an influenza-like illness is defined as close contact with a person in the same household or residential setting who has had recent symptoms of influenza.

People who are not effectively protected by vaccination include:

• those who have not been vaccinated since the previous influenza season

• those for whom vaccination is contraindicated, or in whom it has yet to take effect

• those who have been vaccinated with a vaccine that is not well matched (according to information from the Health Protection Agency) to the circulating strain of influenza virus.

During localised outbreaks of influenza-like illness (outside the periods when national surveillance indicates that influenza virus is circulating generally in the community), oseltamivir and zanamivir may be used for post-exposure prophylaxis in at-risk people living in long-term residential or nursing homes, whether or not they are vaccinated. However, this should be done only if there is a high level of certainty that the causative agent in a localised outbreak is influenza, usually based on virological evidence of infection with influenza in the index case or cases.

Oseltamivir and zanamivir are not recommended for seasonal prophylaxis of influenza.

Amantadine is not recommended for the prophylaxis of influenza.