Seasonal Flu

What You Should Know for the 2012-2013 Influenza Season

Questions & Answers

What should I do during flu season?

As always, get a flu vaccine every year. Getting vaccinated is the first and most important step in protecting against this serious disease. Vaccination efforts should continue as long as influenza viruses are circulating.

Also, you can help stop the spread of influenza and other diseases by doing the following things:

If you get sick with flu-like illness, stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.)
Practice proper cough and sneeze etiquette to prevent the spread of germs.
Wash your hands regularly.
Avoid touching your eyes, nose or mouth
Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill.

While not a substitute for vaccination, these steps can help prevent the spread of respiratory viruses like influenza.

And remember, there are antiviral drugs that can treat flu illness. They can make your illness milder and help you feel better faster. They also can prevent serious flu-related complications, like pneumonia. For more information about antiviral drugs, visit Treatment - Antiviral Drugs.

Find out if you are at high risk of developing influenza-related complications if you get the flu. See People Who Are at High Risk of Developing Flu-Related Complications for a complete list.

How well is the vaccine working this season?

CDC conducts studies each year to determine how well the vaccine protects against illness. These estimates provide more information about how well this season’s vaccine is working.

Findings from early data suggest that this season’s vaccine so far is reducing the risk of having to go to the doctor for influenza by about 60% for vaccinated people. The data are published in “ Early Estimates of Seasonal Influenza Vaccine Effectiveness — United States, January 2013,” in the January 11, 2013, Morbidity and Mortality Weekly Report.

These estimates are within the range of what is expected during seasons when most circulating influenza viruses characterized by CDC are like the viruses included in the vaccine, which is what we are seeing this season. These findings also are similar to those published in a recent meta-analysis, which summarized the benefits of influenza vaccines using data from randomized controlled clinical trials. Influenza vaccination, even with moderate effectiveness of about 60%, has been shown to also reduce the following: flu-related illness, antibiotic use, time lost from work, hospitalizations, and deaths.

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Is vaccine still available?

Flu vaccine is produced by private manufacturers, so availability depends on when production is completed. Information about the number of seasonal influenza vaccine doses distributed this season is available at Seasonal Influenza Vaccine & Total Doses Distributed.

In May and September, 2012, influenza vaccine manufacturers originally projected about 135 million doses would be available for the U.S. market during the 2012-2013 season. Recent updates from manufacturers to CDC indicate that more doses of flu vaccine were actually produced, totaling 145 million doses. As of February 8, 2013, 134.8 million doses had been distributed. (During 2011-2012, 132.8 million doses of flu vaccine were distributed in the United States.)

At this time, some vaccine providers may have exhausted their vaccine supplies, while others may have remaining supplies of vaccine. People seeking vaccination may need to call more than one provider to locate vaccine. The flu vaccine locator may be helpful.

Does CDC recommend prioritizing remaining supplies of flu vaccine?

No, CDC does not have a recommendation to prioritize remaining supplies of flu vaccine at this time. CDC continues to recommend influenza vaccination for all people 6 months and older. It also continues to be especially important that people at high risk of influenza complications get vaccinated, including pregnant women, children under 5 years but especially younger than 2 years, older adults 65 years and older, and people with chronic conditions like asthma, diabetes, and heart disease.

Are there supply concerns with antiviral drugs this season?

On January 10, 2013, the U.S. Food and Drug Administration (FDA) released information indicating there may currently be intermittent shortages of Oseltamivir Phosphate (Tamiflu) for Oral Suspension (6mg/mL 60 mL), due to increased demand for the drug. This is the pediatric suspension (liquid). The manufacturer has instructions for pharmacists on how to compound an oral suspension from Tamiflu 75 mg (adult) capsules. These instructions provide for an alternative oral suspension when commercially manufactured oral suspension formulation is not readily available.

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When will flu activity peak?

The timing of flu is very unpredictable and can vary from season to season. Flu activity most commonly peaks in the United States in January or February. However, seasonal flu activity can begin as early as October and continue to occur as late as May. The 2011-2012 season began late and was relatively mild compared with previous seasons (see 2011-2012 Flu Season Draws to a Close for more information). The 2012-2013 influenza season began relatively early compared to recent seasons (see Press Briefing Transcript: U.S. Influenza Activity and Vaccination Rates for Current Season) and by January 11, 2013, flu activity was high across most of the United States. It is not possible to predict when the season will peak or how severe the 2012-2013 season will be, but based on past experience, it’s likely that flu activity will continue for some time. During the past 10 influenza seasons, the proportion of people visiting doctors for influenza-like illness (ILI) remained at or above baseline for an average of 12 consecutive weeks, with a range of 1 week (2011-2012 season) to 16 weeks (2005-2006 season). During the pandemic, the proportion of visits to doctors for ILI remained above the national baseline for 19 consecutive weeks.

Are new flu viruses circulating this season?

Flu viruses are constantly changing so it's not unusual for new flu viruses to appear. For more information about how flu viruses change, visit How the Flu Virus Can Change. CDC analyzes influenza viruses that are circulating each season to see whether they are like the viruses included in that season's vaccine. This so-called “antigenic characterization” data is published weekly in FluView. So far, most of the influenza viruses that have been analyzed at CDC are like the viruses included in the 2012-2013 influenza vaccine. However, some influenza B viruses that have been analyzed by CDC do not match the influenza B virus included in the 2012-2013 vaccine.

(See FluView for more information).

Should I still get vaccinated since flu season has started?

Yes. CDC recommends that people get vaccinated against influenza as long as influenza viruses are circulating. Influenza seasons are unpredictable and can begin as early as October, and substantial activity can occur as late as May.

It takes about two weeks after vaccination for antibodies to develop in the body that provide protection against the flu.

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Should I still get vaccinated even if I have already gotten sick with the flu?

Yes. There are a couple of reasons why you should be vaccinated even if you have already been sick with a flu-like illness this season. First, it’s possible that your illness was not caused by an influenza virus. There are other respiratory viruses circulating along with flu that can have similar flu symptoms. The only way to know for sure that a flu virus is making you sick is to have a sample taken and tested in a laboratory. Second, even if you were sick with one influenza virus, the seasonal flu vaccine protects against three types of flu viruses that research suggests will be most common. This means the vaccine can offer protection against other influenza viruses you haven’t been exposed to yet.

Can I get vaccinated and still get influenza?

Yes. It’s possible to get sick with influenza even if you have been vaccinated (although you won’t know for sure unless you get a positive influenza test). This is possible for the following reasons:

You may be exposed to an influenza virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (About 2 weeks after vaccination, antibodies that provide protection develop in the body.)
You may be exposed to an influenza virus that is not included in the seasonal flu vaccine. There are many different influenza viruses that circulate every year. The composition of the flu shot is reviewed each season and updated if needed to protect against the three viruses that research suggests will be most common. Characterization of influenza viruses collected this season in the United States indicates that most circulating viruses are like the vaccine viruses; however, there is a smaller percentage of viruses that the vaccine would not be expected to protect against.
Unfortunately, some people can get infected with an influenza virus the flu vaccine is designed to protect against despite getting vaccinated. Protection provided by influenza vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, the flu vaccine works best among young healthy adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. While vaccination offers the best protection against influenza infection, it's still possible that some people may become ill after being vaccinated. Influenza vaccination is not a perfect tool, but it is the best tool currently at our disposal to prevent influenza.

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Has CDC received reports of people who have gotten a flu vaccine and then tested positive for influenza?

Yes. CDC has received reports of some people who were vaccinated against influenza becoming ill and testing positive for influenza. This occurs every season. This is an early season, with more influenza activity being reported at this time than has been seen during recent flu seasons. CDC is watching the situation closely and will provide additional information as it becomes available. There are, however, a number of reasons why people who got an influenza vaccine may still get influenza this season, see Can I get vaccinated and still get influenza.

To estimate how well influenza vaccines work each year, CDC has been working with researchers at universities and hospitals since the 2004-2005 influenza season conducting observational studies using laboratory-confirmed influenza as the outcome.

For the latest interim data on effectiveness of this year’s vaccine, see How well is the vaccine working this season?

It’s important that health care providers and the public remember that influenza antiviral medications are available to treat influenza. CDC has recommendations on the use of these medications (sold commercially as “Tamiflu®” and “Relenza®”). Antiviral treatment as early as possible is recommended for any patients with confirmed or suspected influenza who are hospitalized, seriously ill, or ill and at high risk of serious influenza-related complications, including young children, people 65 and older, people with certain underlying medical conditions and pregnant women. Treatment should begin as soon as influenza is suspected, regardless of vaccination status or rapid test results and should not be delayed for confirmatory testing. A full list of people considered at high risk for serious influenza complications is available at People at High Risk of Developing Flu–Related Complications. More information about antiviral drugs and CDC’s recommendations are available at Antiviral Drugs.

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Is this season's vaccine a good match for circulating viruses?

Over the course of a flu season, CDC studies samples of flu viruses circulating during that season to evaluate how close a match there is between viruses used to make the vaccine and circulating viruses. Data are published in the weekly FluView.

As of the first week in January 2013, most (91%) of the influenza viruses that have been analyzed at CDC are like the viruses included in the 2012-2013 influenza vaccine. The match between the vaccine virus and circulating viruses is one factor that impacts how well the vaccine works.

More Questions about Vaccine

Where can I get a flu vaccine?

Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.

Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.

What kinds of vaccines have been made available in the United States for 2012-2013?

A number of different manufacturers produced trivalent (three component) influenza vaccines for the U.S. market, including intramuscular (IM), intradermal, and nasal spray vaccines. See Key Facts About Seasonal Flu Vaccine for more information about the different types of vaccine made available in the United States. Some manufacturers are planning to produce a quadrivalent (four component) vaccine for the 2013-2014 season.

Who produces influenza vaccine for the United States?

Influenza vaccine for the United States is produced by a number of different vaccine manufacturers and licensed by the Food and Drug Administration. The CDC does not produce flu vaccine.

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Why do I need a flu vaccine every year?

A flu vaccine is needed every year because flu viruses are constantly changing. It’s not unusual for new flu viruses to appear each year. The flu vaccine is formulated each year to keep up with the flu viruses as they change.

Also, multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time.

Getting vaccinated each year provides the best protection against influenza throughout flu season.

How long does a flu vaccine protect me from getting the flu?

First, it's important to note that how well the flu vaccine protects against influenza illness can vary for a number of reasons. (See “How effective is the flu vaccine?”). In terms of the duration of immunity, multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. The decline in antibodies is influenced by several factors, including the antigen used in the vaccine, and the person's general health (for example, certain chronic health conditions may have an impact on immunity). When most healthy people with regular immune systems are vaccinated, their bodies produce antibodies and they are protected throughout the flu season, even as antibody levels decline over time. People with weakened immune systems may not generate the same amount of antibodies after vaccination. In addition, their antibody levels may drop more quickly when compared to healthy people.

For everyone, getting vaccinated each year provides the best protection against influenza throughout flu season. It’s important to get a flu vaccine every year, even if you got vaccinated the season before and the viruses in the vaccine have not changed for the current season.

For additional information about declining immunity after vaccination, please see the studies listed below.

Ambrose CS, Tingling Y, Walker RE, Connor EM. Duration of protection provided by live attenuated influenza vaccine in children. Pediatr Infect Dis J 2008;27:744-748.
Kûnzel W et al. Kinetics of humoral antibody response to trivalent inactivated split influenza vaccine in subjects previously vaccinated or vaccinated for the first time. Vaccine 1996; 14: 1108-1110.
Ochiai H, Shibata M, Kamimura K, Niwayama S. Evaluation of the efficacy of split-product trivalent A(H1N1), A(H3N2), and B influenza vaccines: Reactogenicity, immunogenicity, and persistence of antibodies following two doses of vaccines. Microbiol Immunol 1986;30(11):1141-1149.
Song JY et al. Long-term immunogenicity of influenza vaccine among the elderly: Risk factors for poor immune response and persistence. Vaccine 2010; 28: 3929-3935.

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What flu viruses does the vaccine protect against?

Flu vaccines are designed to protect against the three influenza viruses that research indicates will be the most common during the upcoming season. Three kinds of influenza viruses commonly circulate among people today: influenza B viruses, influenza A (H1N1) viruses, and influenza A (H3N2) viruses. Each year, one flu virus of each kind is used to produce seasonal influenza vaccine.

The 2012-2013 influenza vaccine is made to protect against the following three viruses:

an A/California/7/2009 (H1N1)pdm09-like virus;
an A/Victoria/361/2011 (H3N2)-like virus;
a B/Wisconsin/1/2010-like virus (from the B/Yamagata lineage of viruses).

Note: The H1N1 virus is the same as the H1N1 virus that was included in the 2011-2012 vaccine, but the influenza H3N2 and B vaccine viruses are different.

More information about influenza vaccines is available at Preventing Seasonal Flu With Vaccination.

In what years was there a good match between the vaccine and the circulating viruses?

In recent years the match between the vaccine viruses and those identified during the flu season has usually been good. In 18 of the last 22 U.S. influenza seasons the viruses in the influenza vaccine have been well matched to the predominant circulating viruses. Since 1990, there has only been one season (1997-98) when there was very low cross-reaction between the viruses in the seasonal vaccine and the predominant circulating virus, and three seasons (1992-93, 2003-04, and 2007-08) when there was low cross-reaction.

It's not possible to predict with certainty which flu viruses will predominate during a given season. Flu viruses are constantly changing (called “antigenic 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. CDC analyzes influenza viruses that are circulating each season to see whether they are like the viruses included in that season's vaccine. This so-called “antigenic characterization” data is published weekly in FluView.

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Can the vaccine provide protection even if the vaccine is not a "good" match?

Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness.

In addition, it's important to remember that the flu vaccine contains three virus viruses so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other viruses.

For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination. This is particularly important for people at high risk for serious flu complications, and their close contacts.

I have heard of people who don’t get vaccinated against influenza in September or October because they want it to “last” through the entire influenza season. Should people wait until later in the influenza season to be vaccinated?

CDC recommends that influenza vaccination begin as soon as vaccine becomes available in the community and continue throughout the flu season. It takes about two weeks after vaccination for antibodies to develop in the body that provide protection against influenza, and influenza seasons can begin as early as October. Therefore, CDC recommends that vaccination begin as soon as vaccine becomes available to ensure that as many people as possible are protected before flu season begins.

Were there any new recommendations for the 2012-2013 influenza season?

No substantive changes to the Advisory Committee on Immunization Practices (ACIP) influenza vaccine recommendations were made for the 2012-2013 influenza season.

Recommendations are available at Seasonal Influenza Vaccination Resources for Health Professionals.

Visit the What’s New web page to sign up and receive updates from the CDC Influenza site.

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Who should get vaccinated?

Everyone who is at least 6 months of age should get a flu vaccine this season. It’s especially important for some people to get vaccinated. Those people include the following:

People who are at high risk of developing serious complications like pneumonia if they get sick with the flu
- This includes
  - People who have certain medical conditions including asthma, diabetes, and chronic lung disease.
  - Pregnant women.
  - People 65 years and older.
People who live with or care for others who are high risk of developing serious complications
- This includes household contacts and caregivers of people with certain medical conditions including asthma, diabetes, and chronic lung disease.

A detailed list is available at Who Should Get Vaccinated Against Influenza. A complete list of health and age factors that are known to increase a person’s risk of developing serious complications from flu is available at People Who Are at High Risk of Developing Flu-Related Complications.