Contact Us
- 800–CDC–INFO
- (800-232-4636)
- 888–232–6348 (TTY)
- cdcinfo@cdc.gov
Questions & Answers
Antiviral Drugs for Seasonal Flu
What are flu antiviral drugs?
Flu antiviral drugs are drugs that decrease the ability of flu viruses to reproduce. While getting a flu vaccine each year is the best way to protect you from the flu, antiviral drugs can be used as a second line of defense to treat the flu or to prevent flu infection.
What are the treatment benefits of flu antiviral drugs?
For treatment, antiviral drugs should be started within 2 days after becoming sick. When used this way, these drugs can reduce the severity of flu symptoms and shorten the time you are sick by 1 or 2 days. They also may make you less contagious to other people.
How effective are antiviral drugs at preventing the flu?
When used to prevent the flu, antiviral drugs are about 70% to 90% effective. It’s important to remember that flu antiviral drugs are not a substitute for getting a flu vaccine.
What flu antiviral drugs does CDC recommend for use in the United States for the 2008-09 season?
CDC and the Advisory Committee on Immunization Practices (ACIP) recommend that oseltamivir (brand name Tamiflu®) or zanamavir (brand name Relenza®) should be used for the treatment and prevention of flu in the United States this season. Although amantadine and rimantadine (two other influenza antiviral drugs) also are FDA-approved for treatment or prevention of influenza, these two drugs are NOT recommended for use in the United States during the 2008-09 flu season because recent flu viruses are resistant to these drugs. When viruses are resistant to drugs, the drugs don’t work or don’t work as well.
Who should take antiviral drugs for flu?
CDC has provided guidelines for health care professionals on the use of antiviral drugs (see Information for Health Care Professionals: Using Antiviral Agents for Seasonal Influenza). In general, antiviral drugs can be offered to anyone who wants to avoid and/or treat the flu, people who are at high risk of serious flu-related complications may benefit most from these drugs. Also, close contacts of people with the flu who are at high risk of serious flu-related complications may benefit from antiviral drugs to protect them from getting sick.
How can I get an antiviral drug for flu?
Antiviral drugs must be prescribed by a health care professional.
How long should antiviral drugs be taken?
The length of time antiviral drugs should be taken depends on how they are being used. To prevent flu, antiviral drugs should be taken for as long as flu viruses are circulating in a given setting. To treat flu, oseltamivir and zanamivir are taken for 5 days. See Treatment & Prevention: Influenza Antiviral Drugs for more information.
What side effects can occur with flu antiviral drugs?
Side effects differ for each drug. If an antiviral drug has been prescribed for you, ask your doctor to explain how to use the drug and any possible side effects. Health care professionals prescribing flu antiviral drugs should alert patients about adverse events that can occur. For more information about side effects, see Antiviral Drugs: Summary of Side Effects.
Can flu antiviral drugs help with other illnesses such as the common cold?
No. Flu antiviral drugs only work against flu viruses. They will not help reduce symptoms from the common cold or any other flu-like illnesses caused by viruses other than flu viruses. Many other viruses cause winter illnesses besides the flu.
Can people who are not in a high-risk group receive antiviral drugs?
Yes. Consult with your doctor to determine if you should take antiviral drugs this season.
Can antiviral drugs be helpful for people unable to take the flu vaccine?
Yes. CDC and ACIP recommend use of antiviral drugs for people allergic to eggs (which can cause them to have an allergic reaction to the vaccine) or for people who previously have encountered complications from Guillain-Barre syndrome (GBS) associated with influenza vaccination. In addition, taking antiviral drugs may be recommended among persons that may not have a good immune response to the flu vaccine.
Should people use antiviral drugs before or after receiving the live attenuated influenza vaccine (LAIV) called FluMist®?
LAIV is one of two types of flu vaccine. It is given as a nasal spray and contains weakened, live virus. Flu antiviral drugs taken from 48 hours before through 2 weeks after getting LAIV can lower or prevent the vaccinated person from responding to the vaccine and the person may not get immune protection from the vaccine.
Antiviral drugs can be taken with the inactivated (i.e. killed) flu vaccine.
Can antiviral drugs be given even if a person is not tested for flu or if a flu test does not indicate that they have influenza?
Yes. For individual patients, influenza testing is not required for antiviral drugs to be prescribed. Testing is done based on health care provider recommendations.
Tests are available that can test for flu viruses in as little as 30 minutes or less. Flu testing can be used to rapidly confirm the flu as the cause of outbreaks. However, results from these rapid tests are not 100% accurate; the test may indicate that a person does not have influenza even though they really do have the flu. So, other information in addition to influenza test results, if done, need to be factored into decisions about using antiviral drugs. One consideration will be information about influenza circulating in the community in general.
What are Tamiflu® (oseltamivir) and Relenza® (zanamivir)?
Tamiflu® and Relenza® are chemically related antiviral drugs known as neuraminidase inhibitors that fight against both influenza A and B viruses.
Oseltamivir (brand name Tamiflu ®) is approved to both treat and prevent flu in people one year of age and older.
Zanamivir (brand name Relenza ®) is approved to treat flu in people 7 years and older and to prevent flu in people 5 years and older.
What are the possible side effects of Tamiflu® (oseltamivir)?
Tamiflu® has been in use since 1999. The most common side effects are nausea and vomiting which usually happen in the first 2 days of treatment. Taking Tamiflu® with food can reduce the chance of getting these side effects. On November 13, 2006, a new precaution about Tamiflu® was added. The precaution warns that people with the flu, mostly children, may be at an increased risk of self-injury and confusion shortly after taking Tamiflu® and should be closely monitored for signs of unusual behavior. This precaution was added after the FDA received post marketing reports (mostly from Japan) about persons (primarily among children and adolescents) who had purposefully injured themselves or been delirious while using Tamiflu® (oseltamivir) to treat influenza. The reports appear to be uncommon. For more information, visit the Food & Drug Administration's MedWatch page.
What should be done if complications while taking Tamiflu® (oseltamivir) occur?
Contact a health care professional immediately if someone taking Tamiflu® shows any signs of unusual behavior.
What are the possible side effects of Relenza® (zanamivir)?
Relenza® has been in use since 1999. The most common side effects are diarrhea, nausea, sinusitis, runny or stuffy nose, bronchitis, cough, headache, dizziness, and ear, nose and throat infections. Some persons, mostly those who already had a chronic lung disease such as asthma, have reported serious breathing problems such as wheezing or shortness of breath after taking Relenza® (zanamivir). In rare cases, people have had an allergic reaction to the drug, including rashes and edema (a build up of fluid in body-tissue) of the face and throat.
Who is at risk for complications from Relenza® (zanamivir)?
Persons with chronic lung diseases such as asthma or chronic obstructive pulmonary disease are not recommended to use Relenza® (zanamivir), as some patients have reported difficulty breathing after inhaling the drug.
What should be done if complications while taking Relenza® (zanamivir) occur?
If you have side effects while taking Relenza® (zanamivir) talk to your health care provider immediately.
Can influenza antiviral drugs be used in pregnant women?
Oseltamivir and zanamivir are both "Pregnancy Category C" medications, indicating that no studies have been conducted to assess the safety of these drugs for pregnant women. Because of the unknown effects of these drugs on pregnant women and their unborn children, these two drugs should be used during pregnancy only if the potential benefit justifies the potential risk to the unborn child. Physicians considering using one of these drugs in a pregnant woman should consult that drug package insert.
For More Information
Information for Health Care Professionals: Antiviral Agents for Seasonal Influenza
- Page last modified July 17, 2008
- Content Source: Coordinating Center for Infectious Diseases (CCID)
- National Center for Immunization and Respiratory Diseases (NCIRD)
