Antiviral post-exposure influenza prophylaxis

Post exposure prophylaxis with oseltamivir and zanamivir are recommended when all of the following circumstances apply.

• national surveillance schemes indicate that influenza virus is circulating
• the person has been exposed (close contact with a person in the same household or residential setting who has had recent symptoms of influenza) to an influenza-like illness
• the person is in an "at risk" clinical group or aged 65 years or older
• The person is able to start prophylaxis within:
  • 48 hours of contact with an index case if taking oseltamivir
  • 36 hours of contact with an index case if taking zanamivir
  • has not been effectively vaccinated against influenza. That is
    • 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 (1)

Possible exposure of otherwise healthy individuals to patients with influenza (2)

• general hygienic measures should be established to prevent onward transmission of influenza
• chemoprophylaxis is not recommended after potential exposure or exposure to infected patients in otherwise healthy individuals
• patients should be educated about signs and symptoms of severe influenza and be instructed to seek medical attention if disease worsens
• in setting where there is continuous or repeated exposure (institutional, healthcare or other special settings), prophylaxis could be considered by the health care professionals

Possible exposure of individuals with risk factors for influenza to patients with influenza (2)

• practice strict infection control measures to reduce onward transmission of the infection
• in this group (with risk factors for influenza) of patients who have been exposed to a patient with influenza
  • antiviral chemoprophylaxis should be offered if it can be started within 48 hours of last contact for oseltamivir or 36 hours of last contact for zanamivir
  • an alternate is close patient monitoring and prompt diagnosis and treatment of influenza
• the drug of choice is oseltamivir - 75 mg daily for 10 days
• in cases of suspected or known oseltamivir resistance among contacts (on clinical or epidemiological grounds), inhaled zanamivir prophylaxis (10 mg daily) should be administered for 10 days
• both zanamivir and oseltamivir could be prescribed for pregnant women

Possible exposure of severely immunosuppressed individuals to patients with influenza (2)

• practice strict infection control measures to reduce onward transmission of the infection
• In light of the high risk for the development of oseltamivir resistance among H1N1 (2009) strains, full-dose inhaled zanamivir should be offered (if treatment can be started within 36-48 hours of last contact) as chemoprophylaxis in severely immunosuppressed individuals, regardless of the source's antiviral susceptibility

Reference:

• 1. National Institute for Health and Clinical Excellence (NICE) 2008. Oseltamivir, amantadine and zanamivir for the prophylaxis of influenza. (including a review of NICE technology appraisal guidance 67)
• 2. Health Protection Agency (HPA) 2011. Pharmacological treatment and prophylaxis of influenza