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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

Quick Facts for Clinicians on Antiviral Treatments for 2009 H1N1

The Public Health Emergency determination for 2009 H1N1 Influenza expired on June 23, 2010, terminating Emergency Use Authorizations issued during the pandemic, including some related to antiviral medications.

November 4, 2009, 4:00 PM ET

While use of influenza antivirals in the United States has increased during the 2009-2010 flu season, there are still many misconceptions about these medications. Listed below are some key facts to consider when deciding whether a patient needs to be treated with antiviral medication.

It's Not Too Late After 48 Hours

While antiviral treatment is most effective when begun within 48 hours of influenza illness onset, studies have shown that hospitalized patients still benefit when treatment is started with oseltamivir more than 48 hours after illness onset. Outpatients, particularly those with risk factors for severe illness who are not improving, might also benefit from treatment initiated more than 48 hours after illness onset.

Many 2009 H1N1 Patients Can Benefit from Antiviral Treatment

All hospitalized patients with suspected or confirmed 2009 H1N1 should receive antiviral treatment with a neuraminidase inhibitor-either oseltamavir or zanamavir. Moderately ill patients, especially those with risk factors for severe illness, and those who appear to be getting worse can also benefit from neuraminidase inhibitors.

No Risk Factors Does Not Mean No Antiviral Treatment

While antivirals are recommended for treatment of 2009 H1N1 in patients with risk factors for severe disease, some people without risk factors may also benefit from antivirals. In fact, 40% of children and 20% of adults who end up hospitalized with complications of 2009 H1N1 have no risk factors. Clinical judgment is always an essential part of treatment decisions.

Treatment Shouldn't Wait Until Laboratory Confirmation

The earlier antiviral treatment is given, the more effective it is for the patient. If you suspect flu and feel antiviral treatment is warranted, then treat even if the rapid test is negative. Some rapid influenza screening tests may produce false negative results and obtaining more accurate testing results can take more than one day.

Capsules Can Ease Oseltamivir Suspension Shortage

Commercially produced pediatric oseltamivir suspension is in short supply. However, there are ample supplies of children's oseltamivir capsules, which can be mixed with syrup at home. Pharmacies can also compound adult oseltamivir capsules into a suspension for treatment of ill infants and children. Additional information on compounding can be found at:


  1. Harper SA et al. Seasonal influenza in adults and children-diagnosis, treatment, chemoprophylaxis, and institutional outbreak management: clinical practice guidelines of the Infectious Diseases Society of America. Clinical Infectious Diseases 2009 Apr 15;48(8):1003-1032.
  2. McGeer A et al. Antiviral therapy and outcomes of influenza requiring hospitalization in Ontario, Canada. Clinical Infectious Diseases 2007 Dec 15;45(12):1568-1575.
  3. Lee N et al. Factors associated with early hospital discharge of adult influenza patients. Antiviral Therapy 2007;12(4):501-508.
  4. Kaiser L et al. Impact of oseltamivir treatment on influenza-related lower respiratory tract complications and hospitalizations. Archives of Internal Medicine 2003 Jul 28;163(14):1667-1672.
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