Questions and Answers:
from the CDC
The 2007-2008 Flu Season
What sort of flu season is expected this year?
Flu seasons are unpredictable in a number of ways. Although epidemics of flu happen every year, the timing of the flu season and its severity depend on many factors, including what influenza viruses are circulating and how well viruses in the vaccine match circulating influenza viruses.
From October 2007 through early January 2008, the United States experienced low levels of flu activity. Beginning in January, influenza activity began increasing. By the week ending February 2, 2008, 31 states were reporting widespread influenza activity.
CDC’s Influenza Division collects, compiles and analyzes information on influenza activity in the United States each week from October through May. New surveillance information is posted weekly at: Flu Activity & Surveillance.
What recommendations are CDC making about flu this season?
To reduce the substantial burden of influenza on the U.S., CDC recommends a three-pronged approach:
Take time to get a vaccine. Vaccination now can still provide protection against influenza this season since different influenza viruses can circulate as late as May.
Take everyday preventive steps like frequent hand washing and covering your cough to help keep germs from spreading.
Take antiviral drugs if your doctor says to. Antiviral drugs are an important second line of defense against influenza and they can be used to treat or prevent influenza virus infection.
Information and materials on these measures, including downloadable flyers and audio announcements, as well as information on how to locate available influenza vaccine for purchase, are available at: Preventing Seasonal Flu.
What can we expect this season in terms of bacterial co-infections, including Staphylococcus aureus, with flu?
Bacterial infections can occur as co-infections with influenza or occur following influenza infection. Last year, CDC noted an increase in flu and Staphylococcus aureus (S. aureus) co-infections among children who had died or were hospitalized with influenza infection. Some of those infections were with methicillin-resistant S. aureus (MRSA). CDC is working with state and local public health authorities to monitor and investigate flu-S. aureus co-infections, including pneumonias and other types of S. aureus infections. On January 30, 2008 CDC issued a Health Advisory on Influenza-Associated Pediatric Mortality and Staphylococcus aureus co-infection. For more information about flu and staph infections visit Seasonal Flu and Staph Infection.
Vaccination remains the best method for preventing flu and its potentially severe secondary complications. Influenza antiviral medications are also available for the treatment of influenza. For more information about treatment, visit Treatment and Prevention: Influenza Antiviral Drugs.
Are new strains of influenza circulating so far this season?
Influenza viruses are constantly changing so it’s common for new strains of influenza viruses to appear each year. For more information about how influenza viruses change, visit How the Flu Virus Can Change. Although influenza A (H1N1) viruses predominated early in the season, an increasing proportion of influenza viruses subtyped have been influenza A (H3N2) viruses. H3N2 viruses are typically associated with more severe illness. An H3N2 virus called A/Brisbane has been detected among the H3N2 viruses in the U.S. that have been tested this season. A/Brisbane is the virus strain that predominated in Europe and the southern hemisphere during their last flu season. The A/Brisbane strain is related to, but is a “drifted” variant from the A/Wisconsin strain included in the 2007-08 vaccine. It is too early to tell how widely A/Brisbane will circulate in the U.S. or how well this year’s vaccine will protect against this strain. However, previous influenza studies have found that while a less than ideal match between the viruses in the vaccine and circulating viruses can reduce the vaccine’s effectiveness, the vaccine can still protect enough to make illness milder and prevent flu-related complications.
How effective is the flu vaccine?
The effectiveness of the vaccine depends in part on the match between the viruses in the vaccine and influenza viruses that are circulating in the community. If these are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different, but related strains of influenza viruses. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?
Will this season’s vaccine be a good match for circulating viruses?
It’s not possible to predict with certainty which influenza viruses will predominate during a given season or what the severity, timing, or duration of a flu season will be. Influenza viruses are constantly changing (called drift) – they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. (For more information about the vaccine virus selection process visit, Selecting the Viruses in the Influenza (Flu) Vaccine.) Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses in the vaccine.
Over the course of a flu season CDC studies samples of influenza viruses circulating during that season to evaluate how close a match there is between viruses in the vaccine and circulating viruses. In addition, CDC conducts vaccine effectiveness studies to determine the vaccine’s effectiveness.
As of February 2, 2008, nearly all H1N1 viruses tested to date at CDC were well-matched to the H1N1 vaccine strain. However, most of the H3N2 and B virus strains were different from those contained in the vaccine, suggesting that protection against circulating H3N2 and B virus strains may not be optimal. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different, but related strains of influenza viruses. Weekly updates on circulating influenza strains are available.
Can the vaccine provide protection even if the vaccine is not a “good” match?
Yes, antibodies made in response to vaccination with one strain of influenza viruses can provide protection against different, but related strains. A less than ideal match may result in reduced vaccine effectiveness against the variant viruses, but it still can provide enough protection to prevent or lessen illness severity and prevent flu-related complications. In addition, it’s important to remember that the influenza vaccine contains three virus strains so the vaccine can also protect against the other two viruses. For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend influenza vaccination. This is particularly important for people at high risk for serious flu complications and their close contacts.
How often are the vaccine and circulating virus strains well matched?
In recent years the match between the vaccine viruses and those identified during the flu season has usually been good. In 16 of the last 19 U.S. influenza seasons, the viruses in the influenza vaccine have been well matched to the predominant circulating viruses. Since 1988, in fact, there has only been one season (1997-98) when there was very low cross-reaction between the viruses in the vaccine and the predominate circulating virus and two seasons (2003-04 and 1992-93) when there was low cross-reaction.
What actions can I take to protect myself and my family against the flu this season?
A flu vaccine is the first and best defense against influenza. However, antiviral drugs are an important second line of defense against the flu. They can be used to treat the flu or to prevent infection with flu viruses. Treatment with antiviral drugs should begin within 48 hours of getting sick, and can reduce your symptoms and shorten the time you are sick. When used for prevention, antiviral drugs are 70% to 90% effective in preventing infection with influenza viruses. Two FDA-approved influenza antiviral agents are recommended for use in the United States to treat or prevent flu during the 2007-08 influenza season: oseltamivir and zanamivir.
In addition, you can take everyday preventive steps like frequent hand washing to decrease your chances of getting the flu. If you are sick with flu, reduce your contact with others and cover your cough to help keep germs from spreading.
What have we seen so far during the 2007-2008 season in terms of antiviral resistance monitoring or surveillance in the United States?
CDC laboratory surveillance has indicated continued high resistance among influenza virus isolates to the adamantanes (amantadine and rimantadine) in the United States. As of February 2, 2008, 99% of influenza A (H3N2) viruses and 8.3% of influenza A (H1N1) viruses were resistant to the adamantanes.
In addition, as of February 2, 2008, CDC has detected 8.1% of H1N1 viruses were resistant to the antiviral drug oseltamivir (brand name Tamiflu®). No oseltamivir resistant influenza A (H3N2) or B viruses have been found in the United States this season and resistance to zanamivir has not been detected. CDC continues to track this information and updated antiviral resistance figures are available in the Weekly U.S. Influenza Surveillance Report, FluView.
As of February 2, 2008, 4.5% of all influenza viruses analyzed by CDC this season have been found to be resistant to oseltamivir. Of those, 8.1% of H1N1 viruses and 0% of H3N2 viruses have been resistant to the antiviral drug oseltamivir. Because influenza activity in the U.S. is just beginning to increase, relatively few viruses have been studied so far. CDC continues to track this information and updated antiviral resistance figures are available in the Weekly U.S. Influenza Surveillance Report, FluView.
Has there been antiviral resistance to oseltamivir before?
Yes, laboratory surveillance during last season showed that 0.7% of H1N1 viruses isolated and studied at CDC were resistant to oseltamivir.
What does this mean?
At this time, only a small number of viruses have been tested, and it is unknown whether antiviral resistance will increase as influenza activity increases and more viruses are tested.
Is CDC recommending any changes to the current guidance on the use of antivirals for the 2007-08 influenza season?
No, CDC is not recommending any changes to the current guidance on the use of influenza antivirals. CDC and the Advisory Committee on Immunization Practices (ACIP) recommend that oseltamivir (brand name Tamiflu®) or zanamivir (brand name Relenza®) can 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 2007-08 flu season because many recent flu viruses are resistant to these drugs. This guidance can be found in Prevention & Control of Influenza – Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2007 Jul 13;56(RR06):1-54. Also available as PDF.
CDC will continue to monitor the situation as additional information is collected.
Preventing Seasonal Flu
What can I do to protect myself against the flu?
By far, the single best way to prevent the flu is for individuals, especially people at high risk for serious complications from the flu, to get a vaccination each fall. To learn more, see Key Facts about Flu Vaccine.
What are other steps that can be taken to prevent the flu?
There are other good health habits that can help prevent the flu. These are:
Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.
If possible, stay home from work, school, and errands when you are sick. You will help prevent others from catching your illness.
Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.
Washing your hands often will help protect you from germs.
Avoid touching your eyes, nose or mouth. Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.
Also, antiviral medications may be used to prevent the flu. See Questions and Answers: Antiviral Medications.
Can herbal, homeopathic or other folk remedies protect against the flu?
There is no scientific evidence that any herbal, homeopathic or other folk remedies have any benefit against influenza.
How long can human influenza viruses remain viable on inanimate items (such as books and doorknobs)?
Studies have shown that human influenza viruses generally can survive on surfaces for between 2 and 8 hours.
What kills influenza virus?
Influenza virus is destroyed by heat (167-212°F [75-100°C]). In addition, several chemical germicides, including chlorine, hydrogen peroxide, detergents (soap), iodophors (iodine-based antiseptics), and alcohols are effective against influenza viruses if used in proper concentration for sufficient length of time. For example, wipes or gels with alcohol in them can be used to clean hands. The gels should be rubbed until they are dry.
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 2007-08 season?
CDC and the Advisory Committee on Immunization Practices (ACIP) recommend that oseltamivir (brand name Tamiflu®) or zanamivir (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 2007-08 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.