sharon sanders
Editor-in-Chief & President
Influenza Antiviral Drug Resistance
On this page?
What is antiviral resistance?
Antiviral resistance means that a virus has changed in such a way that the antiviral drug is less effective in treating or preventing illnesses. In the United States, four antiviral drugs are FDA-approved for use against influenza: amantadine, rimantadine, zanamivir (Relenza?) and oseltamivir (Tamiflu?). The adamantane drugs (amantadine and rimantadine) are approved for influenza A, while the neuraminidase inhibitor drugs (zanamivir and oseltamivir) are approved for both influenza A and influenza B. CDC issues guidance for health care providers on which antiviral drugs to use each flu season.
How does antiviral resistance happen?
The ability to constantly change is a hallmark of influenza viruses. Flu viruses often change from one season to the next and can even change within the course of one flu season. As an influenza virus replicates (i.e., make copies of itself), the genetic makeup may change in a way that results in the virus becoming resistant to one or more of the antiviral drugs used to treat or prevent influenza.
How is antiviral resistance detected?
CDC routinely collects viruses through a domestic and global surveillance system to monitor for changes in influenza viruses. Samples of viruses collected from around the United States and worldwide are studied to determine if they are resistant to any of the four FDA-approved influenza antiviral drugs.
What is CDC doing to monitor antiviral resistance in the United States?
CDC conducts ongoing surveillance and testing of influenza viruses to monitor for antiviral resistance in collaboration with state public health departments and the World Health Organization (WHO). The information collected is used in making informed public health policy recommendations about the use of influenza antiviral medications.
How does CDC improve monitoring of influenza viruses for antiviral resistance?
CDC continually improves the ability to rapidly detect and monitor antiviral resistance through improvements in laboratory methods and by increasing the number of surveillance sites domestically and globally and increasing the number of laboratories that can test for resistance. Enhanced surveillance efforts have provided CDC with the capability to detect resistant strains more quickly, and enabled CDC to monitor for changing trends over time.
How is this surveillance information used?
Enhanced surveillance efforts have provided CDC with the capability to detect resistant strains more quickly, and enabled CDC to monitor for changing trends overtime. Virus surveillance information is helpful in making recommendations on which antiviral drugs should be used for treating or preventing flu.
How did influenza antiviral resistance patterns change during the 2009?2010 influenza season?
By the end of the 2009-2010 season, almost all (98.9%) of tested 2009 pandemic H1N1 viruses were susceptible to oseltamivir (Tamiflu?), and all of the viruses tested were susceptible to zanamivir (Relenza?). In addition, all of the 2009 pandemic H1N1 viruses were resistant to amantadine and rimantadine. This information facilitated the guidance to use either oseltamivir or zanamivir during the pandemic. The rare 2009 pandemic H1N1 viruses that were oseltamivir-resistant shared a single genetic mutation that caused them to be resistant to the drug.
What have we seen so far during the 2010-2011 season in terms of antiviral resistance monitoring in the United States?
To date, 2009 pandemic H1N1, influenza A (H3N2) and influenza B viruses have been detected by surveillance. All three virus strains typically are sensitive to oseltamivir and zanamivir, but the influenza A strains have been resistant to the adamantanes (the adamantanes have never had activity against influenza B viruses). While, sporadic oseltamivir-resistant 2009 pandemic influenza A (H1N1) virus infections were identified during 2009-2010 and can be expected this year, the public health impact of oseltamivir-resistant 2009 H1N1 virus infections has been limited to date. Ongoing surveillance for oseltamivir-resistance and resistance to other neuraminidase inhibitors among influenza viruses is essential.
What antiviral drugs are recommended for use during the 2010-2011 flu season?
Antiviral medications currently recommended include oseltamivir (Tamiflu?) and zanamivir (Relenza?), based upon recent viral surveillance and resistance data. These data indicate that more than 99% of currently circulating influenza virus strains are sensitive to these medications. Updates on antiviral resistance surveillance are available for clinicians at: http://www.cdc.gov/flu/weekly/.
What implications does antiviral resistance have for the U.S. antiviral stockpile that was created as part of the United States pandemic plan?
The U.S. antiviral drug stockpile contains both neuraminidase inhibitor agents, oseltamivir and zanamivir. These medications are to be used in the event that a novel influenza A subtype virus, such as the 2009 pandemic H1N1 or avian influenza A (H5N1) virus, emerges and spreads easily among humans. During the 2009-2010 H1N1 pandemic, antiviral drugs were used to treat infection with the 2009 (H1N1) influenza A virus.
The stockpile is for the control of pandemic influenza, and is not for the treatment of infection by seasonal influenza. Resistance among seasonal strains does not predict resistance among pandemic influenza viruses.
Antiviral drugs, such as oseltamivir, are one component of a multi-faceted approach to pandemic preparedness planning and response. The effectiveness of any drug during a pandemic is difficult to predict, as it is not possible to know which virus will cause the next pandemic.
Oseltamivir remains the drug recommended by the World Health Organization (WHO) as the first-line influenza antiviral drug for the treatment of patients infected with influenza A (H5N1).
A very small number of patients infected with 2009 influenza (H1N1) A virus or avian influenza A (H5N1) virus had evidence of oseltamivir resistance in viruses that were isolated from them. In these cases, the oseltamivir-resistant viruses did not spread to others.
CDC will continue ongoing surveillance and testing of influenza viruses for antiviral resistance among seasonal and novel influenza viruses such as H5N1 viruses.
For more information about the U.S. antiviral drug stockpile, visit Antiviral Drug Distribution and Use
.
http://www.cdc.gov/flu/about/qa/antiviralresistance.htm?s_cid=ccu122710_008
On this page?
- What is antiviral resistance?
- How does antiviral resistance happen?
- How is antiviral resistance detected?
- What is CDC doing to monitor antiviral resistance in the United States?
- How does CDC improve monitoring of influenza viruses for antiviral resistance?
- How is this surveillance information used?
- How did influenza antiviral resistance patterns change during the 2009-2010 influenza season?
- What have we seen so far during the 2010-2011 season in terms of antiviral resistance monitoring in the United States?
- What antiviral drugs are recommended for use during the 2010-2011 flu season?
- What implications does antiviral resistance have for the U.S. antiviral stockpile that was created as part of the United States pandemic plans?
What is antiviral resistance?
Antiviral resistance means that a virus has changed in such a way that the antiviral drug is less effective in treating or preventing illnesses. In the United States, four antiviral drugs are FDA-approved for use against influenza: amantadine, rimantadine, zanamivir (Relenza?) and oseltamivir (Tamiflu?). The adamantane drugs (amantadine and rimantadine) are approved for influenza A, while the neuraminidase inhibitor drugs (zanamivir and oseltamivir) are approved for both influenza A and influenza B. CDC issues guidance for health care providers on which antiviral drugs to use each flu season.
How does antiviral resistance happen?
The ability to constantly change is a hallmark of influenza viruses. Flu viruses often change from one season to the next and can even change within the course of one flu season. As an influenza virus replicates (i.e., make copies of itself), the genetic makeup may change in a way that results in the virus becoming resistant to one or more of the antiviral drugs used to treat or prevent influenza.
How is antiviral resistance detected?
CDC routinely collects viruses through a domestic and global surveillance system to monitor for changes in influenza viruses. Samples of viruses collected from around the United States and worldwide are studied to determine if they are resistant to any of the four FDA-approved influenza antiviral drugs.
What is CDC doing to monitor antiviral resistance in the United States?
CDC conducts ongoing surveillance and testing of influenza viruses to monitor for antiviral resistance in collaboration with state public health departments and the World Health Organization (WHO). The information collected is used in making informed public health policy recommendations about the use of influenza antiviral medications.
How does CDC improve monitoring of influenza viruses for antiviral resistance?
CDC continually improves the ability to rapidly detect and monitor antiviral resistance through improvements in laboratory methods and by increasing the number of surveillance sites domestically and globally and increasing the number of laboratories that can test for resistance. Enhanced surveillance efforts have provided CDC with the capability to detect resistant strains more quickly, and enabled CDC to monitor for changing trends over time.
How is this surveillance information used?
Enhanced surveillance efforts have provided CDC with the capability to detect resistant strains more quickly, and enabled CDC to monitor for changing trends overtime. Virus surveillance information is helpful in making recommendations on which antiviral drugs should be used for treating or preventing flu.
How did influenza antiviral resistance patterns change during the 2009?2010 influenza season?
By the end of the 2009-2010 season, almost all (98.9%) of tested 2009 pandemic H1N1 viruses were susceptible to oseltamivir (Tamiflu?), and all of the viruses tested were susceptible to zanamivir (Relenza?). In addition, all of the 2009 pandemic H1N1 viruses were resistant to amantadine and rimantadine. This information facilitated the guidance to use either oseltamivir or zanamivir during the pandemic. The rare 2009 pandemic H1N1 viruses that were oseltamivir-resistant shared a single genetic mutation that caused them to be resistant to the drug.
What have we seen so far during the 2010-2011 season in terms of antiviral resistance monitoring in the United States?
To date, 2009 pandemic H1N1, influenza A (H3N2) and influenza B viruses have been detected by surveillance. All three virus strains typically are sensitive to oseltamivir and zanamivir, but the influenza A strains have been resistant to the adamantanes (the adamantanes have never had activity against influenza B viruses). While, sporadic oseltamivir-resistant 2009 pandemic influenza A (H1N1) virus infections were identified during 2009-2010 and can be expected this year, the public health impact of oseltamivir-resistant 2009 H1N1 virus infections has been limited to date. Ongoing surveillance for oseltamivir-resistance and resistance to other neuraminidase inhibitors among influenza viruses is essential.
What antiviral drugs are recommended for use during the 2010-2011 flu season?
Antiviral medications currently recommended include oseltamivir (Tamiflu?) and zanamivir (Relenza?), based upon recent viral surveillance and resistance data. These data indicate that more than 99% of currently circulating influenza virus strains are sensitive to these medications. Updates on antiviral resistance surveillance are available for clinicians at: http://www.cdc.gov/flu/weekly/.
What implications does antiviral resistance have for the U.S. antiviral stockpile that was created as part of the United States pandemic plan?
The U.S. antiviral drug stockpile contains both neuraminidase inhibitor agents, oseltamivir and zanamivir. These medications are to be used in the event that a novel influenza A subtype virus, such as the 2009 pandemic H1N1 or avian influenza A (H5N1) virus, emerges and spreads easily among humans. During the 2009-2010 H1N1 pandemic, antiviral drugs were used to treat infection with the 2009 (H1N1) influenza A virus.
The stockpile is for the control of pandemic influenza, and is not for the treatment of infection by seasonal influenza. Resistance among seasonal strains does not predict resistance among pandemic influenza viruses.
Antiviral drugs, such as oseltamivir, are one component of a multi-faceted approach to pandemic preparedness planning and response. The effectiveness of any drug during a pandemic is difficult to predict, as it is not possible to know which virus will cause the next pandemic.
Oseltamivir remains the drug recommended by the World Health Organization (WHO) as the first-line influenza antiviral drug for the treatment of patients infected with influenza A (H5N1).
A very small number of patients infected with 2009 influenza (H1N1) A virus or avian influenza A (H5N1) virus had evidence of oseltamivir resistance in viruses that were isolated from them. In these cases, the oseltamivir-resistant viruses did not spread to others.
CDC will continue ongoing surveillance and testing of influenza viruses for antiviral resistance among seasonal and novel influenza viruses such as H5N1 viruses.
For more information about the U.S. antiviral drug stockpile, visit Antiviral Drug Distribution and Use
.http://www.cdc.gov/flu/about/qa/antiviralresistance.htm?s_cid=ccu122710_008