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Frequently asked questions on use of influenza A(H1N1) 2009 monovalent vaccines (2009 H1N1 monovalent influenza vaccines): Practical considerations for immunization programs and providers

This website is archived for historical purposes and is no longer being maintained or updated. For updated information on the current flu season, see the CDC Seasonal Flu website.

November 10, 2009, 4:30 PM ET

Two different influenza vaccines are available this influenza season, and many people will be recommended to receive both the seasonal influenza vaccine and the 2009 influenza A (H1N1) 2009 monovalent vaccine (referred to in this document as 2009 H1N1 monovalent influenza vaccine). Below are some practical considerations for use of influenza vaccines. This information is only intended to address the current flu season and might change as the situation unfolds. This information is not intended to be applied to routine use during future seasonal influenza vaccination efforts.

Children ages 6 months through 8 years receiving seasonal influenza vaccination for the first time are recommended to receive 2 doses. However, in the prescribing information (package inserts) for 2009 H1N1 monovalent influenza vaccines, children ages 6 months through 9 years are recommended to receive 2 doses. Does CDC recommend that clinicians follow the recommendation in the 2009 H1N1 monovalent vaccine package inserts or use the standard seasonal vaccine recommendations?

The recommendations for use of seasonal vaccine are unchanged – children 6 months through 8 years receiving seasonal influenza for the first time are recommended to receive 2 doses. Other children just need one dose of seasonal influenza vaccine.

Using the 2009 H1N1 monovalent influenza vaccine schedule presented in the prescribing information is recommended (6 months through 9 years receive 2 doses regardless of earlier vaccination with seasonal influenza vaccine).

The interval between doses stated in the 2009 H1N1 monovalent influenza vaccine prescribing information is "approximately 1 month". What does "approximately 1 month" mean?

CDC recommends that the two doses of 2009 H1N1 monovalent vaccines be separated by 28 days (4 weeks).

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The 2009 H1N1 monovalent influenza vaccine trials that are currently underway have often used a 21 day (3 week) interval between doses. Is a 21 day interval acceptable for inactivated 2009 H1N1 monovalent vaccines?

CDC recommends that the two doses of 2009 H1N1 monovalent influenza vaccines be separated by 28 or more days (4 weeks). However, trials of the inactivated 2009 H1N1 vaccines have often used a 21 day interval. Administering the two doses of a 2009 H1N1 monovalent inactivated influenza vaccine at least 21 days apart is safe and acceptable. Therefore, if the second dose of an inactivated 2009 H1N1 monovalent vaccine is separated from the first dose by at least 21 days, the second dose can be considered valid. If the interval separating the doses is less than 21 days, the second dose should be repeated 28 or more days after the invalid (second) dose (≥ 21 days is acceptable for this interval also).

Can the seasonal inactivated vaccine (trivalent inactivated vaccine or TIV) and the 2009 H1N1 monovalent inactivated vaccine be given at the same visit?

Yes.

If seasonal LAIV and 2009 H1N1 monovalent LAIV are inadvertently given at the same visit, do either or both doses need to be repeated, and if so, when?

Seasonal LAIV and 2009 H1N1 monovalent LAIV should not be administered at the same visit. While use of the 2 types of LAIV at the same visit could result in reduced immunogenicity for one vaccine, according to some experts, there are no data describing what happens with the vaccine response following simultaneous administration of LAIV vaccines. However, if both types of LAIV are inadvertently administered at the same visit neither vaccine, needs to be repeated.

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What is the minimum interval between doses of seasonal LAIV and 2009 H1N1 monovalent LAIV?

There are no data on sequential administration of seasonal and 2009 H1N1 monovalent LAIV. The ACIP recommends a minimum interval of 28 days (4 weeks) between use of a seasonal LAIV and a 2009 H1N1 monovalent LAIV because these are considered to be 2 different vaccines. The ACIP recommendations were developed based on data from studies using attenuated injectable live virus vaccines such as the measles, mumps and rubella vaccine. Trials of 2009 H1N1 live attenuated vaccines have used a 28 day interval between doses and therefore, 28 days is the recommended interval between 2 doses of LAIV (seasonal and H1N1 monovalent LAIV). However, based on previous studies of LAIV replication and immune response, as little as 14 days (2 weeks) might be sufficient to allow for an appropriate immune response to both vaccines. Therefore, an interval between the two types of LAIV of 2 weeks or more may be acceptable, although an interval of 28 days is preferred.

If seasonal LAIV and 2009 H1N1 monovalent 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 monovalent LAIV should not be administered at the same visit, and should be separated by at least 28 days (14 days acceptable based on previous studies of attenuated influenza vaccine virus replication and immune response). If accidentally given at the same visit, neither dose needs to be repeated. If given 1-13 days apart, the second dose should be repeated 28 days (14 days acceptable) from the invalid (second) dose.

Can a live attenuated vaccine be given at the same visit as an inactivated influenza vaccine (e.g., seasonal LAIV and 2009 H1N1 monovalent inactivated vaccine, or 2009 H1N1 monovalent LAIV and seasonal trivalent inactivated influenza vaccine [TIV])?

Yes, based upon ACIP’s recommendations, these two types of vaccines can be given at the same visit.

Can a child who requires 2 doses of a 2009 H1N1 monovalent influenza vaccine and who received the first dose with an inactivated 2009 H1N1 monovalent vaccine complete the series with the 2009 H1N1 monovalent LAIV, or vice versa?

There are limited data describing the immune response to mixed schedules. Therefore, when feasible, the same type of vaccine (live attenuated or inactivated) should be used in a two-dose schedule. Mixed schedules however, are preferable to not completing the series. A 28 day interval between doses is recommended, but 21 days is acceptable. If vaccines are separated by 1-20 days, repeat the invalid (second) dose 28 days (21 days acceptable) from the invalid second dose.

Should we set aside doses of 2009 H1N1 monovalent vaccine to administer as second doses to children 6 months through 9 years?

No. 2009 H1N1 monovalent influenza vaccine availability is expected to increase during the next several weeks, so vaccine should not be held in reserve for patients who already have received 1 dose but might require a second dose.

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