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A flu vaccine is the single best way to protect against influenza illness. This season, there is a seasonal flu vaccine to protect against seasonal flu viruses and a 2009 H1N1 vaccine to protect against the 2009 H1N1 influenza virus (sometimes called “swine flu”).

This page contains information about the 2009 H1N1 flu vaccine.

There are two kinds of 2009 H1N1 vaccines being produced:

• A 2009 H1N1 “flu shot” — an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The indications for who can get the 2009 H1N1 flu shot are the same as for seasonal flu shots. The flu shot is approved for use in people 6 months of age and older, including healthy people, people with chronic medical conditions and pregnant women. The same manufacturers who produce seasonal flu shots are producing 2009 H1N1 flu shots for use in the United States this season. The 2009 H1N1 flu shot is being made in the same way that the seasonal flu shot is made.

• The 2009 H1N1 nasal spray flu vaccine — a vaccine made with live, weakened viruses that do not cause the flu (sometimes called LAIV for “live attenuated influenza vaccine”). The indications for who can get the 2009 H1N1 nasal spray vaccine are the same as for seasonal nasal spray vaccine. LAIV is approved for use in healthy* people 2 years to 49 years of age who are not pregnant. The nasal spray vaccine for use in the United States is being made by MedImmune, the same company that makes the seasonal nasal spray vaccine called “FluMist®.” The 2009 H1N1 nasal spray vaccine is being made in the same way as the seasonal nasal spray vaccine.

About 2 weeks after vaccination, antibodies that provide protection against 2009 H1N1 influenza virus infection will develop in the body.

The 2009 H1N1 vaccine will not protect against seasonal influenza viruses.

When to Get Vaccinated
Vaccination against 2009 H1N1 should begin as soon as vaccine is available and continue throughout the influenza season, into December, January, and beyond. This is because the timing and duration of flu activity can vary. Flu seasons can last as late as April or May. By early October 2009, extensive 2009 H1N1 flu activity was being reported in the United States. It’s possible that there may be waves of 2009 H1N1 activity during the 2009-2010 flu season that hit communities more than once over the course of the season. While 2009 H1N1 viruses are likely to be the most common cause of influenza this season, CDC still expects that seasonal influenza viruses will circulate and continues to recommend that people get a seasonal flu vaccine to protect against seasonal flu viruses. The ACIP has issued separate recommendations on who should get the 2009-10 seasonal vaccine

Vaccine Supply
The U.S. government has purchased 250 million doses of 2009 H1N1 vaccine, so anyone who wants to get the vaccine will have the opportunity to do so. Vaccine will be made available as quickly as possible as it rolls off the production lines, so initially, the vaccine will be available in limited quantities.

Who Should Get Vaccinated
CDC’s Advisory Committee on Immunization Practices (ACIP), a panel made up of medical and public health experts, met July 29, 2009, to make recommendations on who should receive the 2009 H1N1 vaccine when it becomes available. While the federal government has purchased enough vaccine so that anyone who wants to get vaccinated can, ACIP’s statement on the “Use of Influenza A (H1N1) 2009 Monovalent Vaccine” recommends that vaccination efforts should focus first on people in five target groups who are at higher risk for 2009 H1N1 influenza or related complications, are likely to come in contact with influenza viruses as part of their occupation and could transmit influenza viruses to others in medical care settings, or are close contacts of infants younger than 6 months (who are too young to be vaccinated). These five target groups make up an estimated 159 million people in the United States.

Initial Target Groups Are:
When vaccine is first available, ACIP recommends that programs and providers administer vaccine to people in the following five target groups (order of target groups does not indicate priority):

• pregnant women,
• people who live with or provide care for infants younger than 6 months (e.g., parents, siblings, and day care providers),
• health care and emergency medical services personnel,
• people 6 months through 24 years of age, and,
• people 25 years through 64 years of age who have certain medical conditions that put them at higher risk for influenza-related complications.

No shortage of 2009 H1N1 vaccine is expected, but vaccine availability and demand can be unpredictable and initially the vaccine may be available in limited quantities.  Because the amount of vaccine available at first will be small, the ACIP also made recommendations regarding which people within the groups listed above should be prioritized if the vaccine is initially available in extremely limited quantities. For more information see the ACIP recommendations on the Use of Influenza A (H1N1) 2009 Monovalent Vaccine at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr58e0821a1.htm

Once the demand for vaccine for the target groups has been met at the local level, ACIP recommends that programs and providers begin vaccinating everyone from the ages of 25 through 64 years. Current studies indicate that the risk for infection among persons 65 and older is less than the risk for younger age groups. However, once vaccine demand among younger age groups has been met, ACIP recommends that programs and providers should offer vaccination to people 65 or older.

The ACIP has issued separate recommendations on who should get the 2009-10 seasonal vaccine.

Who Should Not Be Vaccinated
There are some people who should not get any flu vaccine without first consulting a physician. These include:

• People who have a severe allergy to chicken eggs.
• People who have had a severe reaction to an influenza vaccination.
• People who developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an influenza vaccine previously. (For information, see General Questions and Answers on Guillain-Barré syndrome (GBS).
• Children younger than 6 months of age (influenza vaccine is not approved for this age group), and
• People who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated.)

Vaccine Effectiveness
The ability of a flu vaccine to protect a person depends on the age and health status of the person getting the vaccine, and the similarity or “match” between the viruses or virus in the vaccine and those in circulation. CDC analyzes circulating inflluenza viruses on an ongoing basis to determine how closely matched they are to vaccine viruses and publishes the information weekly in FluView. In addition,  every year CDC monitors vaccine effectiveness. For more information about flu vaccine effectiveness, see How Well Does the Seasonal Vaccine Work?

Vaccine Side Effects (What to Expect)
The same side effects typically associated with the seasonal flu shot and the seasonal nasal spray vaccine are expected with the 2009 H1N1 flu shot and 2009 H1N1 nasal spray vaccine.

These are:

The flu shot: The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. Some minor side effects that could occur are:

• Soreness, redness, or swelling where the shot was given
• Fever (low grade)
• Aches

If these problems occur, they begin soon after the shot, are usually mild, and usually last 1 to 2 days. Almost all people who receive influenza vaccine have no serious problems from it. However, on rare occasions, flu vaccination can cause serious problems, such as severe allergic reactions.

The nasal spray: The viruses in the nasal-spray vaccine are weakened and do not cause severe symptoms often associated with influenza illness. (In clinical studies, transmission of vaccine viruses to close contacts has occurred only rarely.)
In children, side effects from LAIV can include:

• runny nose
• wheezing
• headache
• vomiting
• muscle aches
• fever

In adults, side effects from LAIV can include

• runny nose
• headache
• sore throat
• cough

For more information about vaccine side effects and safety see General Questions and Answers on 2009 H1N1 Influenza Vaccine Safety.

More Information

• 2009 H1N1 Flu Shot: Vaccine Information Statement (VIS)
• 2009 H1N1 Nasal Spray: Vaccine Information Statement (VIS)
• Seasonal Flu Shot: Vaccination Information Statement (VIS)
• Seasonal Nasal Spray: Vaccination Information Statement (VIS)