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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

Questions & Answers

Vaccine against 2009 H1N1 Influenza Virus

Recommendations for Vaccine against 2009 H1N1 Influenza Virus

Will the vaccine against 2009 H1N1 influenza virus (also called "swine flu") be the same vaccine in 2010?

Yes, the vaccine to protect against the 2009 H1N1 influenza virus will be the same for the entire 2009-2010 influenza season, which extends into the spring of 2010. The "2009" in the name only relates to the year the virus was first identified; it does not have to do with how long the vaccine will work or the year in which it should be administered. The 2009 H1N1 virus is not included in the 2009-2010 seasonal flu vaccine because it was identified after manufacturers had started making the seasonal flu vaccine.

Who should get the 2009 H1N1 influenza vaccine?

When vaccine to protect against 2009 H1N1 first became available, supplies were limited. For this reason, CDC’s Advisory Committee on Immunization Practices (ACIP) recommended that people at highest risk for complications from this virus, or those caring for high risk individuals who cannot receive vaccination, receive the vaccine first. These target groups included pregnant women, people who live with or care for children younger than 6 months of age, health care and emergency medical services personnel, anyone 6 months through 24 years of age, and people ages of 25 through 64 years of age at higher risk for 2009 H1N1 influenza because of certain chronic health conditions or compromised immune systems.

ACIP recognized the need to assess supply and demand issues at the local level. The committee further recommended that once the demand for vaccine for these target groups had been met at the local level, programs and providers should begin vaccinating everyone from ages 25 through 64 years. Studies at that time indicated that the risk for infection among people 65 and older was less than the risk for younger age groups so people 65 and older were not initially targeted to receive early doses of vaccine. However, ACIP noted that as vaccine supply increased and demand for vaccine among younger age groups is being met, programs and providers should also offer vaccination to people over the age of 65. At this time, many states have already opened up vaccination to anyone who wants it and while people 65 and older are still less likely to get sick with 2009 H1N1, severe infections and deaths have occurred in every age group, including older people. CDC is now encouraging those who have been patiently waiting to receive the 2009 H1N1 vaccine, including people 65 and older, to get vaccinated depending on local supply.

Separate recommendations are available for seasonal influenza, (Who Should Get Vaccinated Against Seasonal Influenza?)

How many doses of vaccine are required?

The U.S. Food and Drug Administration (FDA) has approved the use of one dose of vaccine against 2009 H1N1 influenza virus for persons 10 years of age and older. For children who are 6 months through 9 years of age, two doses of the vaccine are recommended. These two doses should be separated by 4 weeks. Infants younger than 6 months of age are too young to get any influenza vaccine.

Why does my child need two doses of the 2009 H1N1 vaccine dose?

The recommendation that children younger than 10 years old receive 2 doses of 2009 H1N1 vaccine was based on studies of immune response to the vaccine as measured by levels of protective antibodies in the blood. After 1 dose of vaccine, infants and young children do not make as many antibodies compared with older children and adults who get 1 dose. 

In addition, effectiveness of seasonal flu vaccine is much less for young children who have never been vaccinated before and only get 1 dose, compared with young children who have never been vaccinated before and get 2 doses. 

Persons who have some antibody from previous vaccination or exposure to infection with another related flu strain will have much greater increases in antibody to flu vaccines. Studies that looked at blood samples taken from children before the pandemic indicate that very few children had any measurable immunity against 2009 H1N1 prior to the outbreak Therefore, all children younger than 10 should get 2 doses regardless of whether they ever have been given seasonal influenza vaccine

What is the recommended interval between the first and second dose for children 6 months through 9 years of age?

CDC recommends that the two doses of vaccine against 2009 H1N1 influenza virus be separated by 4 weeks. However, if the second dose is separated from the first dose by at least 21 days, the second dose can be considered valid.

A few months have past since my child received the first 2009 H1N1 vaccine, should I have her receive the 2nd dose?

CDC recommends that the two doses of vaccine against 2009 H1N1 influenza virus be separated by 4 weeks. If the second dose is administered beyond 4 weeks, the body’s immune system still remembers the first dose and develops antibodies or protection against 2009 H1N1 influenza virus.  Research shows that the immune system will not develop adequate protection if the vaccine dosing interval is < 21 days.

Can people who are allergic to eggs receive the vaccine against 2009 H1N1 influenza virus?

People who are allergic to eggs might be at risk for allergic reactions from receiving any influenza vaccine. People who have had any of the following symptoms or experiences should consult with a doctor or other medical professional before considering any influenza vaccination:

  • hives or swelling of the lips or tongue after eating eggs
  • acute respiratory distress (trouble breathing) after eating eggs
  • documented hypersensitivity to eggs, including those who have had asthma related to egg exposure at their workplace or other allergic responses to egg protein

Because children with severe asthma are at high risk of serious complications from influenza, a regimen has been developed for giving influenza vaccine to children with severe asthma and egg hypersensitivity.

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Late Season Recommendations

Why should flu be taken seriously?

Flu should never be dismissed as “just the flu.” It’s a serious disease, and while most cases are mild, some can be deadly.  So far this flu season, most flu activity has been caused by the 2009 H1N1 virus, which was first identified in April 2009 and caused the first flu pandemic in 40 years.

Because many people with influenza illness are not tested for flu or are tested late in their illness, methods have been developed to estimate the numbers of people with influenza illness and with influenza-related complications, including hospitalizations and deaths.  CDC estimates that from April to January 16, 2010, approximately 57 million cases of 2009 H1N1 occurred in the United States, including 257,000 H1N1-related hospitalizations and about 11,690 deaths. 

With 2009 H1N1, approximately 90% of estimated hospitalizations and 87% of estimated deaths from April through January 16, 2010 occurred in people younger than 65 years old.  In contrast, with seasonal influenza, about 60% of seasonal flu-related hospitalizations and 90% of flu-related deaths occur in people 65 years and older.   This data confirms that the 2009 H1N1 impacted younger adults and children more than older adults compared to seasonal flu.  However, people in all age groups can develop severe illness from either seasonal flu or from 2009 H1N1.

Flu season seems to be dying down—Why do people still need a vaccination against 2009 H1N1?

The flu season is not over yet. As recently as January 15, 7 states were still reporting regional flu activity, so flu is still out there. Also, seasonal flu typically peaks in February and March and influenza activity can occur as late as May. So, increased activity from either seasonal flu, 2009 H1N1 or both are still possible this season.
For example, during the 1957-58 pandemic, flu activity dropped in December and January. Public health officials assumed the worst was over, and stopped encouraging people to get vaccinated. Then flu activity increased abruptly in February and March, and hospitalizations and deaths increased as well.

That was an important lesson—even if flu activity dies down in January, as it has this year, the season is not over. It’s still important to get vaccinated against the flu and be as prepared as possible if activity increases again this season.

Is there anyone who should take priority when it comes to getting a flu vaccination?

Right now there is enough vaccine for everyone who hasn’t been vaccinated and wants to be. Children who are 9-years old or younger need two doses of vaccine about a month apart. There is enough vaccine for them as well.

But it is especially important for certain groups of people to get vaccinated. If you have certain underlying health conditions—such as asthma, heart disease, or diabetes—or if you’re pregnant, you’re at greater risk of complications from flu. If you’re over 65, you’re also at risk of complications.

If you’re a health care worker, you should get vaccinated. If you care for or live with an infant under 6 months of age (babies less than 6 months old are too young to be vaccinated), you should get vaccinated, too, to prevent spreading the flu to people who are vulnerable.

Where should I go to get vaccinated against 2009 H1N1?

This is a very good time to get vaccinated. Right now not many people are sick, and there is enough vaccine for everyone who hasn’t been vaccinated yet—including kids 9 years old and younger who need a second dose.

An easy way to find out where vaccine is available in your area is by going to and clicking on the vaccine locator. In addition, has a new Facebook application—the “Flu Fighter.” It’s one of the site’s many “viral” communication tools to help spread the word that getting a vaccine against 2009 H1N1 is the best way to protect yourself and your friends. When you go to please check it out.

If the second dose of 2009 H1N1 flu vaccine for children under 10 years of age is given over a month after the first dose, is it still considered effective?

Yes. CDC recommends that the two doses of vaccine against 2009 H1N1 influenza virus be separated by 4 weeks. However, if the second dose is separated from the first dose by at least 21 days, the second dose can be considered valid.

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Supply and Distribution

How do "project areas" know how much vaccine is available for them to order?

CDC distributes vaccine to 62 "project areas." These project areas include 50 states, the District of Columbia, 8 U.S. territories and freely associated states, and 3 large metropolitan areas. CDC sends these project areas an allocation report each morning on how much of each formulation of vaccine against 2009 H1N1 influenza virus is available for them to order.

What is the number of doses “allocated” for ordering?

The number of doses "allocated" for ordering is the amount that is at the distribution depots and ready for states to order. The quantity of vaccine allocated is based on the project area's population size. As an example, if 6 million doses total (3 million doses of nasal spray vaccine AND 3 million doses of injectable vaccine) are ready for ordering nationally (as of today) and a state has 10% of the US population, then their allocation for today is 600,000 doses total (300,000 doses of the nasal spray vaccine and 300,000 doses of injectable vaccine).

How is vaccine shipped to project areas?

CDC’s contractor for centralized distribution ships vaccine directly to hospitals, clinics, doctor’s offices, health departments, and other providers of vaccines that have been designated by the project area.

What kind of providers can be designated by project areas to receive vaccine?

Project areas are responsible for registering vaccine providers in their jurisdiction. Providers may include, but are not limited to, individual clinicians, provider offices, clinics at places of work, hospitals, local health departments, retail pharmacies, and community vaccinators. Providers or facilities receiving vaccine must be capable of receiving and properly storing vaccine.

What is the number of doses “allocated” for ordering?

The number of doses "allocated" for ordering is the amount that is at the distribution depots and ready for states to order. The quantity of vaccine allocated is based on the project area's population size. As an example, if 6 million doses total (3 million doses of nasal spray vaccine AND 3 million doses of injectable vaccine) are ready for ordering nationally and a state has 10% of the US population, then their allocation for today is 600,000 doses total (300,000 doses of the nasal spray vaccine and 300,000 doses of injectable vaccine).

Who determines which providers receive the vaccine?

Specific determinations about where vaccine will be shipped and how it will be distributed to providers are made at the state and local level. The federal government allocates vaccine based on population to public health departments in the 62 project areas. These public health departments then make decisions about how to distribute vaccine to providers equitably and efficiently within their jurisdictions with the goal of reaching the priority groups first. State and local immunization programs have planned their efforts according to local capacity and needs. CDC continues to encourage state and local health officials to review and revise their vaccine distribution plans in response to changing needs.

How does CDC ensure that providers’ vaccination practices are consistent with ACIP recommendations?

Providers who offer the vaccine against 2009 H1N1 influenza virus must sign an agreement stating that they will adhere to recommendations issued by the U.S. Advisory Committee on Immunization Practices (ACIP).

How many sites can a project area designate to receive vaccine?

There is a maximum of 150,000 sites to which vaccine can be shipped via the centralized distribution system. Project areas have received information about their allocation of sites.

What should project areas expect with respect to frequency of vaccine shipments?

Vaccine is shipped as it becomes available, taking into account state allocations and orders. The process is modeled after that utilized by immunization programs to order seasonal influenza vaccine off the federal contract. Details about CDC's ordering/allocation process for seasonal influenza are described in the all-grantee message sent to immunization program grantees on August 11, 2009 (Grantee message for allocation).

What is the minimum dose order for shipments of 2009 H1N1 vaccine?

For each vaccine formulation (identified by its National Drug Code) the minimum dose order is 100 doses and all orders must be placed in increments of 100 doses. Each ancillary supply kit contains supplies to support 100 doses of vaccine, with different kits available for prefilled syringe products and for multi-dose vial products.

When was the vaccine against the 2009 H1N1 virus first available and how much was available?

Both the injected vaccine (flu shot) and nasal spray forms of the vaccine against the 2009 H1N1 virus were produced and licensed by the Food and Drug Administration. The vaccine first became available in early October, and more doses are becoming available every week. Vaccine availability, however, depends on many factors so these numbers are updated often. The first doses of the nasal spray, or live, attenuated intranasal vaccine (LAIV), were administered on October 5, 2009, and the first doses of the influenza shot were administered the week of October 12.

Where is the vaccine available?

Every state has developed a vaccine delivery plan. Vaccine has been available in a combination of settings such as vaccination clinics organized by local health departments, healthcare provider offices, schools, and other private settings, such as pharmacies and workplaces. For more information, see State/Jurisdiction Contact Information for Health Care Providers Interested in Providing H1N1 Vaccine.

For information on seasonal vaccine supply and distribution, visit Seasonal Influenza Vaccine Supply for the U.S. 2009-2010 Influenza Season.

Can I get vaccinated against the 2009 H1N1 virus at my workplace?

CDC has recommended that when possible worksites offer both influenza vaccines. It also suggests that workplaces consider granting employees time off from work to get vaccinated if not offered at the worksite. For more information on CDC’s influenza guidance for businesses and employers visit: "CDC Guidance for Businesses and Employers To Plan and Respond to the 2009–2010 Influenza Season".

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Vaccines for the 2009-2010 Influenza Season

Does the seasonal influenza vaccine also protect against 2009 H1N1 influenza?

The seasonal influenza vaccine will not protect you against 2009 H1N1 influenza. For more information about the seasonal flu vaccine, read Key Facts About Seasonal Flu Vaccine.

Is this vaccine made differently than the seasonal influenza vaccine?

No. The vaccine against the 2009 H1N1 virus is made using the same processes and facilities that are used to make the currently licensed seasonal influenza vaccines

Can both flu vaccines be given at the same time?

Inactivated vaccine against the 2009 H1N1 flu virus (the flu shot) can be given at the same visit as any other vaccine, including pneumococcal polysaccharide vaccine. The LAIV (nasal spray vaccine) against the 2009 H1N1 virus can be administered at the same visit as any other live or inactivated vaccine EXCEPT seasonal live attenuated influenza vaccine.

Prior Vaccination or Illness

Should I get vaccinated against 2009 H1N1 if I have had flu-like illness since the Spring of 2009?

The symptoms of influenza (flu-like illnesses) are similar to those caused by many other viruses. Even when influenza viruses are causing large numbers of people to get sick, other viruses are also causing illnesses. Specific testing, called “RT-PCR test,” is needed in order to tell if an illness is caused by a specific influenza strain or by some other virus. This test is different from rapid flu tests that doctors can do in their offices. Since most people with flu-like illnesses will not be tested with RT-PCR this season, the majority will not know whether they have been infected with 2009 H1N1 flu or a different virus.

Therefore, if you were ill but do not know if you had 2009 H1N1 infection, you should get vaccinated if your doctor recommends it. So, most people recommended for 2009 H1N1 vaccination should be vaccinated with the 2009 H1N1 vaccine regardless of whether they had a flu-like illness earlier in the year. If you have had 2009 H1N1 flu, as confirmed by an RT-PCR test, you should have some immunity against 2009 H1N1 flu and can choose not to get the 2009 H1N1 vaccine. However, vaccination of a person with some existing immunity to the 2009 H1N1 virus will not be harmful. For more information on flu tests, see Influenza Diagnostic Testing During the 2009-2010 Flu Season.

Any immunity from 2009 H1N1 influenza infection or vaccination will not provide protection against seasonal influenza. All people who want protection from seasonal flu should still get their seasonal influenza vaccine.


Are there other ways to prevent the spread of illness?

Take everyday actions to stay healthy.

  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
  • Wash your hands often with soap and water, especially after you cough or sneeze. If soap and water are not available, use an alcohol-based hand rub.*
  • Avoid touching your eyes, nose or mouth. Germs spread that way.

Stay home if you get sick. CDC recommends that you stay home from work or school and limit contact with others to keep from infecting them. CDC recommends that people with influenza-like illness remain at home until at least 24 hours after they are free of fever (temperature of 100° F [37.8°C] or more), or signs of a fever without the use of fever-reducing medications.

Follow public health advice regarding school closures, avoiding crowds and other social distancing measures. These measures are still important, even with the availability of the vaccine against 2009 H1N1 virus, because they can prevent the spread of other viruses that cause respiratory infections.

What about the use of antivirals to treat 2009 H1N1 infection?

CDC has issued interim guidance for the use of antiviral drugs for this season. CDC also has published Questions & Answers related to the use of antiviral drugs for this season.

Are natural remedies (also referred to as “complementary” or "alternative" medicine) recommended to prevent the 2009 H1N1 Influenza virus?

The first and most important step to prevent influenza is to get vaccinated. Vaccination stimulates an immune response using a killed or weakened virus that uses the body’s own defense mechanisms to prevent infection. CDC's current recommendations to protect against 2009 H1N1 virus do not include natural remedies as a sole prevention method. If you want to use a natural remedy to reduce symptoms, CDC recommends that you talk to your health care provider about options.

Alternative medicine should not be used as a replacement for proven conventional care, or to postpone seeing a doctor about a medical problem. The National Institutes of Health (NIH) provides information on specific alternative options, including scientific information, potential side effects, and cautions for each.

The Federal Trade Commission (FTC) warns consumers to be cautious about products that claim to prevent, treat, or cure 2009 H1N1 influenza, specifically products like pills, air filtration devices, and cleaning agents can kill or eliminate the virus.

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