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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.

H1N1 Clinicians Questions and Answers

April 8, 2010, 11:30 AM EDT

Recommendations for the 2009 H1N1 Vaccine

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

Yes, the vaccine for 2009 H1N1 flu 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 strain is not included in the 2009-2010 seasonal flu vaccine because it was identified after manufacturers had started making the seasonal flu vaccine.

Who is recommended to receive the 2009 H1N1 flu vaccine?

When vaccine first became available, the CDC Advisory Committee on Immunization Practices (ACIP) made recommendations for who should receive the 2009 H1N1 vaccine first. These groups include pregnant women, household and caregiver contacts of children younger than 6 months of age (e.g. parents, siblings, and daycare providers), health care and emergency medical services personnel, persons from 6 months through 24 years of age , and persons aged 25 through 64 years who have medical conditions associated with a higher risk of influenza complications.

Since these groups have now had the chance to receive the 2009 H1N1 vaccine, everyone, including people 65 years and older are now recommended to seek the vaccine.

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Will the 2009 H1N1 vaccine be recommended for patients who had influenza-like illness since spring 2009?

All people in a recommended vaccination target group who did not have 2009 H1N1 virus infection confirmed by real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) test should be vaccinated with the 2009 H1N1 vaccine. People who had an illness confirmed by rRT-PCR to be 2009 H1N1 virus earlier in 2009 can be considered to be immune and do not need to be vaccinated this year. However, most people with respiratory illnesses since this spring have not had testing with the rRT-PCR test, which is the only test that can confirm infection specifically with the 2009 H1N1 virus. Tests such as rapid antigen detection assays and diagnoses based on symptoms alone without rRT-PCR testing, cannot specifically determine if a person has 2009 H1N1 influenza. Although people who were not tested, but who became ill within 1-4 days after close contact with a person with lab confirmed 2009 H1N1 influenza might have been infected with 2009 H1N1, they cannot be certain since many pathogens can cause respiratory illness. These people should get the 2009 H1N1 vaccine as recommended for their age and risk group.
People who were infected with the 2009 H1N1 virus and who are not severely immune compromised will likely have immunity to subsequent infection with 2009 H1N1 virus. However, vaccination of a person with some existing immunity to the 2009 H1N1 virus will not be harmful, and patients who are uncertain about how they were diagnosed should get the 2009 H1N1 vaccine. In addition, people recommended for seasonal vaccine should get a seasonal vaccine because infection with the 2009 H1N1 virus does not provide protection against seasonal influenza viruses.

Supply and Distribution

How can providers obtain 2009 H1N1 flu vaccine?

State/Local public heath departments are responsible for directing the flow of vaccine to providers within every state. They will determine which providers will receive vaccine and will allocate vaccine among providers as it becomes available to them. Information on 2009 H1N1 vaccine distribution plans or on becoming a 2009 H1N1 vaccine provider can be found at your state’s public health department website or the CDC H1N1 website at State Contacts. Public health departments are in the process of determining which providers are interested in administering vaccine. Participating providers will sign a Provider Agreement assuring they intend to meet state requirements.

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When should providers stop offering the 2009 H1N1 flu vaccine?

CDC continues to encourage people to get vaccinated throughout the flu season.  It is important that providers continue to encourage vaccination, especially for those with high risk conditions. CDC also recommends that health departments, providers and pharmacies retain their unexpired 2009 H1N1 vaccine supplies as a reserve, should demand for vaccination increase before seasonal vaccine becomes available. 2009 H1N1 virus is still circulating and continues to cause illness, hospitalizations, and death.

Though flu activity has declined since the late fall, there are still uncertainties surrounding the rest of this flu season, including the possibility of the circulation of seasonal influenza viruses and ongoing circulation of 2009 H1N1 viruses. In past pandemics, flu activity has occurred in waves, and it’s possible that the United States could experience another wave of flu activity in the spring. In addition, sporadic cases of influenza may also be detected in the summer.

Supplies of 2009 H1N1 vaccines are ample and CDC encourages everyone who wants protection against 2009 H1N1 influenza to get vaccinated, including people 65 years and older.

How can providers determine what percentage of their patients plan on getting the 2009 H1N1 vaccine in a physician’s office?

It is difficult to predict where individuals will go to receive the 2009 H1N1 vaccine. However, based on unpublished data from the Adult National Immunization Survey, during the 2006-2007 influenza season, among 19-49 year olds who were vaccinated, approximately 38% of persons at increased risk of complications from influenza reported receiving influenza vaccine in a physician’s office. Approximately 26% of persons with household contact with a high risk person and 25% of persons with no specific indications for influenza vaccine were vaccinated in a physician’s office.

What are some possible approaches a practice might take to administer the 2009 H1N1 vaccine?

Options include holding special clinics, integrating the 2009 H1N1 vaccination into usual care, providing walk-in immunizations, or coordinating with local public health clinics if unable to administer 2009 H1N1 vaccine themselves. In determining the best option, each practice should consider several factors, including availability of vaccine, practice resources and patient demand.

If my patients are vaccinated outside of my practice, how will that information be available for inclusion in the patient’s permanent medical record?

Recipients of the 2009 H1N1 vaccine will be provided with a hand-held card to serve as a record of vaccination and a source of information should a report to the Vaccine Adverse Event Reporting System (VAERS) be needed. Vaccine recipients will be encouraged to bring the hand-held card at their next visit to their primary care provider so that vaccination information can be transcribed into the patient’s permanent medical record.

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Can seasonal influenza vaccine and 2009 H1N1 vaccine be given at the same visit?

Both seasonal and 2009 H1N1 vaccines are available as inactivated and live attenuated (LAIV) formulations. The simultaneous and sequential administration of seasonal and 2009 H1N1 inactivated vaccines is currently being studied; however preliminary results are now available. Existing recommendations are that two inactivated vaccines can be administered at any time before, after, or at the same visit as each other (General Recommendations on Immunization, MMWR 2006;55[RR-15]). Existing recommendations also state that an inactivated and live vaccine may be administered at any time before, after or at the same visit as each other. Consequently, providers can administer seasonal and 2009 H1N1 inactivated vaccines, seasonal inactivated vaccine and 2009 H1N1 LAIV, or seasonal LAIV and inactivated 2009 H1N1 at the same visit, or at any time before or after each other. Live attenuated seasonal and live 2009 H1N1 vaccines should NOT be administered at the same visit until further studies are done. If a person is eligible and prefers the LAIV formulation of seasonal and 2009 H1N1 vaccine, these vaccines should be separated by a minimum of four weeks.

Can 2009 H1N1 vaccine be administered at the same visit as other vaccines?

Inactivated 2009 H1N1 vaccine can be administered at the same visit as any other vaccine, including pneumococcal polysaccharide vaccine. Live 2009 H1N1 vaccine can be administered at the same visit as any other live or inactivated vaccine EXCEPT seasonal live attenuated influenza vaccine.

The age for two doses is different for seasonal (6 months through 8 years) and 2009 H1N1 monovalent vaccine (6 months through 9 years) in the package inserts. Does CDC recommend that clinicians follow the recommendation in the package inserts?

CDC recommends that clinicians follow the guidance in the manufacturer package inserts. For 2009 H1N1 monovalent vaccines, that means that clinicians should administer two doses of 2009 H1N1 monovalent vaccine to children 6 months through 9 years of age. Persons 10 years and older should receive one dose.

The interval between 2009 H1N1 monovalent vaccine doses, for children 6 months through 9 years, is stated as "approximately 1 month" in the package inserts. What does "approximately 1 month" mean?

CDC recommends that the two doses of 2009 H1N1 monovalent vaccine 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 to be valid. If the interval separating the doses is less than 21 days the second dose should be repeated four weeks after the first dose was given.

If seasonal live attenuated influenza vaccine (LAIV) and 2009 H1N1 LAIV are given during the same visit, do either or both doses need to be repeated, and if so, when?

There are no data on the administration of seasonal and 2009 H1N1 LAIV during the same visit. CDC's Advisory Committee on Immunization Practices (ACIP) recommends that seasonal and 2009 H1N1 LAIV not be administered during the same visit. However, if both types of LAIV are inadvertently administered during the same visit, neither vaccine needs to be repeated.

Repeating Doses when Seasonal LAIV and 2009 H1N1 LAIV are Used in Shorter Intervals than is Accepted (between 1 and 13 days) If seasonal and H1N1 LAIV are not administered on the same day, but are separated by less than 14 days (2 weeks), do either or both doses need to be repeated, and if so, when?

Seasonal LAIV and 2009 H1N1 LAIV should not be administered at the same visit, and should be separated by at least 14 days and ideally by at least 28 days based on previous studies of attenuated influenza vaccine virus replication and immune response. If the interval between administration of seasonal LAIV and 2009 H1N1 LAIV is from 1-13 days, the vaccine more recently administered should be repeated.

Can patients who are allergic to eggs receive the 2009 H1N1 flu vaccine?

Asking persons if they can eat eggs without adverse effects is a reasonable way to determine who might be at risk for allergic reactions from receiving influenza vaccines. Persons who have had symptoms such as hives or swelling of the lips or tongue, or who have experienced acute respiratory distress after eating eggs, should consult a physician for appropriate evaluation to help determine if influenza vaccine should be administered. Persons who have documented (IgE)-mediated hypersensitivity to eggs, including those who have had occupational asthma related to egg exposure or other allergic responses to egg protein, also might be at increased risk for allergic reactions to influenza vaccine, and consultation with a physician before vaccination should be considered. A regimen has been developed for administering influenza vaccine to asthmatic children with severe disease and egg hypersensitivity (J Pediatr 1985;106:931-3.).

Can a person who has received LAIV test positive on a rapid influenza diagnostic test?

The live attenuated influenza vaccine viruses in LAIV (seasonal vaccine and 2009 H1N1 monovalent vaccine) can cause a positive result on a rapid influenza diagnostic test. The tests are designed to detect influenza viruses and cannot differentiate between live attenuated and wild-type influenza viruses. A positive test in a person who recently (in the previous 7 days) received LAIV and who also has an influenza-like illness could be caused by either LAIV or wild-type influenza virus.

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Prior Vaccination or Illness

Do those who were previously vaccinated against the 1976 swine influenza need to get vaccinated against the 2009 H1N1 influenza?

The 1976 swine influenza virus and the 2009 H1N1 influenza virus are different enough that it is unlikely a person vaccinated in 1976 will have full protection from the 2009 H1N1 flu virus. People vaccinated in 1976 should still be given the monovalent vaccine against 2009 H1N1.

Are people who have had influenza-like illness since last spring immune from 2009 H1N1?

Most influenza tests, including rapid influenza tests, cannot distinguish between 2009 H1N1 influenza and other types of influenza A viruses. Specialized testing (real-time reverse transcription-polymerase chain reaction [rRT-PCR]) is needed to diagnose infection with 2009 H1N1 virus with any certainty. Therefore, most people who have had an influenza-like illness since the spring of 2009 should not be assumed to have immunity to 2009 H1N1 influenza and should therefore be vaccinated.

Should individuals who may have had 2009 H1N1 influenza virus infection (since spring 2009) be vaccinated now?

All persons for whom vaccination is recommended and who have not had a laboratory-confirmed (i.e., by rRT-PCR) 2009 H1N1 influenza virus infection should be vaccinated with the monovalent vaccine against 2009 H1N1. Those persons for whom vaccination is recommended and who have had a laboratory-confirmed 2009 H1N1 influenza virus infection can be considered to be immune and do not need to receive the monovalent vaccine against 2009 H1N1 this season. However, there is no harm in receiving the 2009 H1N1 vaccine for people who were previously infected with the virus. Persons who are unsure if they had 2009 H1N1 virus infection diagnosed by rRT-PCR should ask their doctor about how the infection was diagnosed (i.e., whether RT-PCR was used).

Can someone who received the 2009 H1N1 influenza vaccine get sick with influenza anyway?

Like any vaccine, the monovalent vaccine against 2009 H1N1 is not expected to be 100% effective, and clinicians should be aware that a history of receipt of this vaccine may not necessarily rule out infection with 2009 H1N1 influenza virus. Vaccination with the monovalent vaccine against 2009 H1N1 is not expected to provide protection against infection with seasonal influenza A or B viruses. Similarly, seasonal influenza vaccination is not expected to prevent infection with 2009 H1N1 influenza virus.

Free Resources

What CDC information will be available for use in practices to help explain the need for both seasonal and 2009 H1N1 vaccine? 

A variety of free resources are available on CDC’s website for 2009 H1N1 vaccine and seasonal flu vaccine, including Vaccine Information Statements.

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