Antiviral medications for influenza

Antiviral medications are available and effective for the treatment and prevention of influenza. However, they do not replace influenza vaccination as the recommended strategy for the control of influenza.1

The neuraminidase inhibitors are the preferred class of antivirals approved for use in New Zealand. They include TAMIFLU® (oseltamivir) and RELENZA® (zanamivir) which are active against influenza A and B viruses. Antiviral resistance to both oseltamivir and zanamivir in circulating influenza viruses is currently low. However, resistance may emerge in some patients (e.g. those who are immunocompromised) in association with treatment. Please refer to the Medsafe website for the TAMIFLU and RELENZA data sheets.

Two new antiviral medications that act against influenza A and B viruses are available overseas but not in New Zealand, intravenous peramivir (neuraminidase inhibitor) and oral baloxavir marboxil (cap-dependent endonuclease inhibitor).2

Guidance on when influenza is circulating in the community can be obtained from regional influenza surveillance reports, these are updated weekly and available at during the season. Antiviral resistance data is included in the report at the end of October and the annual report in March the following year.

Antiviral treatment

TAMIFLU is approved for treatment of influenza in adults and children aged 2 weeks and older. RELENZA is approved for the treatment of adults and children aged 5 years and older.

Limited information regarding the use of TAMIFLU in children from birth to under 1 year of age is available, although it was approved for use during the 2009 pandemic.

Clinical benefit is greatest when antiviral treatment is commenced EARLY, especially within 2 days of influenza illness onset. Clinical trials show that early antiviral treatment can shorten the duration of fever and influenza symptoms, reduces viral shedding and may reduce the risk of complications from influenza including otitis media in children, pneumonia and respiratory failure.3,4 Observational studies during the 2009 pandemic have shown that antiviral treatment commenced within 2–4 days in comparison with 5 or more days may still be beneficial in patients with severe or complicated influenza. Reductions in hospitalisation, respiratory failure, intensive care admission, and mortality have been demonstrated.5,6,7

Treatment indications

Treatment is recommended as early as possible for patients with suspected or confirmed influenza who are hospitalised, have severe influenza, progressive illness or are at higher risk of severe outcomes.

  • Persons at higher risk for influenza complications include those ≥65 years, all ages with chronic respiratory disease, immunosuppression, women who are pregnant or postpartum and residents of nursing homes or chronic care facilities
  • Treatment should start immediately, rather than wait for the results of a virology test 

Seek specialist advice as appropriate, especially for patients with severe or deteriorating influenza.

TAMIFLU is recommended as the first-line antiviral treatment. Standard adult treatment course is:

  • TAMIFLU 1 x 75mg capsule twice daily for 5 days
  • TAMIFLU 75mg capsules are a Pharmacist Only Medicine for the treatment or prophylaxis of influenza in adults and adolescents aged 13 years and older who have been exposed to the influenza virus. 
  • TAMIFLU in all other presentations and use of TAMIFLU in children aged 12 years or under require a prescription from a doctor or nurse practitioner with the relevant prescribing rights.

Recommendations for the second-line use of RELENZA are:

  • RELENZA 2 x 5mg, two inhalations twice a day (a total daily dose of 20mg) for 5 days
  • An inability to take or tolerate TAMIFLU e.g. due to nausea or vomiting
  • Moderate to severe renal impairment

Antiviral chemoprophylaxis

TAMIFLU is approved for prophylaxis of influenza in adults and children aged 1 year and older. RELENZA is approved for prophylaxis of influenza in adults and children aged 5 years and older.

While annual influenza vaccination, given well before the influenza season, is the recommended strategy/approach to prevention and control of influenza, clinical trials have reported that both TAMIFLU and RELENZA were effective in preventing influenza illness in persons following exposure to a household member or other close contact with laboratory confirmed influenza (TAMIFLU 68%-89%; RELENZA 72%-82%).1

Post-exposure indications for use

Routine use of antivirals for pre-exposure or post exposure chemoprophylaxis is not recommended, however there are situations where post-exposure use is indicated.

  • On a case by case basis e.g. for pregnant or postpartum women who have had close contact with an influenza case or other persons at high risk of severe illness
  • For outbreak control among high risk persons in institutional settings e.g. hospitals, residents of nursing homes and other closed institutions.8

Chemoprophylaxis should occur within 48 hours of exposure to an influenza infected person.

Standard adult chemoprophylaxis courses are:

  • TAMIFLU 1 x 75mg capsule daily for 10 days
  • RELENZA 2 x 5mg, two inhalations a day (a total daily dose of 10mg) for 10 days


  1. Fiore, M., et al., Antiviral agents for the treatment and chemoprophylaxis of influenza. Centers for Disease Control and Prevention, 2011.
  2. Centers  for Disease Control and Prevention. Influenza antiviral medications: Summary for clinicians [Internet]. Atlanta: Centers  for Disease Control and Prevention; 2016 [updated 2020 January 15; cited 2020 March 6]. Available from:
  3. Wang, K., et al., Neuraminidase inhibitors for preventing and treating influenza in children (published trials only). Cochrane Database of Systematic Reviews, 2012(4).
  4. Jefferson, T., et al., Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children. Cochrane Database Syst Rev, 2012. 1: p. CD008965.
  5. Siston, A.M., et al., Pandemic 2009 influenza A(H1N1) virus illness among pregnant women in the United States. JAMA, 2010. 303(15): p. 1517 25.
  6. Yu, H., et al., Risk factors for severe illness with 2009 pandemic influenza A (H1N1) virus infection in China. Clin Infect Dis, 2011. 52(4): p. 457-65.
  7. Hsu, J., et al., Antivirals for treatment of influenza: a systematic review and meta-analysis of observational studies. Ann Intern Med, 2012. 156(7): p. 512-24.
  8. Booy, R., et al., Treating and preventing influenza in aged care facilities: a cluster randomised controlled trial. PLoS One, 2012. 7(10): p. e46509.