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IAC Express: Weekly immunization news and information

Issue 1446: September 13, 2019

Ask the Experts: CDC Experts Answer Your Questions

As a thank-you to our loyal IAC Express readers, we periodically publish extra editions such as this one, with new and updated "Ask the Experts" Q&As answered by CDC experts. These questions all relate to influenza vaccination.

IAC extends thanks to our experts: Andrew T. Kroger, MD, MPH; Mark S. Freedman, DVM, MPH, DACVPM; Tina S. Objio, MSN, MHA, RN; Candice L. Robinson, MD, MPH; Raymond A. Strikas, MD, MPH, FACP, FIDSA; and JoEllen Wolicki, BSN, RN, all from the National Center for Immunization and Respiratory Diseases, CDC. 

Influenza Vaccines

Influenza Vaccines

Q: What's new in the 2019–2020 influenza vaccine recommendations?

A: The 2019–2020 ACIP influenza vaccine recommendations were published on August 23, 2019, and are available at The updated guidance: 

  • describes the vaccine composition for this season (a change in the H3N2 and H1N1 vaccine components);
  • discusses recent FDA labeling changes, including expansion of the age indication for Afluria Quadrivalent (Seqirus) to age 6 months and older (previously licensed for people age 5 years and older) and expanding options for Fluzone Quadrivalent (Sanofi Pasteur) dosing for children age 6-35 months to allow either 0.25 mL or 0.5 mL doses.

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Q: Which influenza vaccines will be available during the 2019–2020 influenza season?

A: Multiple manufacturers are producing influenza vaccine for the U.S. market for the 2019–2020 season. Inactivated vaccines will be produced using egg-based, cell culture–based, and recombinant technologies. Most inactivated influenza vaccines will be quadrivalent (containing four strains of influenza virus). The only trivalent vaccines are the high-dose inactivated vaccine (Fluzone-HD, Sanofi) and the MF-59 adjuvanted vaccine (Fluad, Seqirus), both of which are indicated for adults age 65 years and older. The recombinant vaccine (Flublok, Sanofi Pasteur) and live attenuated vaccine (Flumist Quadrivalent, AstraZeneca) are both quadrivalent.  
ACIP does not state a preference for one influenza vaccine over another for people for whom more than one vaccine is recommended and age and health condition appropriate. A complete listing of influenza vaccine products is available at
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Q: What are the differences between trivalent and quadrivalent influenza vaccines?

A: Influenza vaccines produced for the current season will be either trivalent (three components) or quadrivalent (four components). Both types of vaccine contain two A viruses and one B virus. The components of 2019–2020 trivalent vaccines are:

  • A/Brisbane/02/2018 (H1N1)pdm09-like virus (new for the 2019-20 season)
  • A/Kansas/14/2017 (H3N2)-like virus (new for the 2019-20 season)
  • B/Colorado/06/2017-like virus (Victoria lineage). 

Quadrivalent vaccines will contain these three viruses, plus a B/Phuket/3073/2013–like virus (Yamagata lineage).

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Q: If quadrivalent vaccine includes one additional strain, why isn't it preferred for use over trivalent vaccine?

A: Two different types of influenza B virus are likely to cause disease during an influenza season, but trivalent influenza vaccines contain only one type of influenza B virus. The quadrivalent vaccine includes both types of B virus. Not all types of vaccine are likely to be uniformly available in any practice setting or locality. Consequently, ACIP does not express a preference for use of one type of influenza vaccine over another type (that is, quadrivalent over trivalent) for those for whom more than one type of vaccine is indicated and available. Vaccination should not be delayed in order to obtain a specific product when an appropriate one is already available.

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Q: Which formulations of influenza vaccines (e.g., nasal spray live attenuated influenza vaccine (LAIV), inactivated injectable high-dose, inactivated injectable standard-dose, adjuvanted inactivated injectable, and recombinant injectable) are licensed for various age groups?

A: There are multiple manufacturers of influenza vaccine and each may have differences in their product line (for example, licensed age group). ACIP does not state a preference for one influenza vaccine over another for people for whom more than one vaccine is recommended and age and health condition appropriate. IAC has developed a handout that summarizes each of the products available for the current influenza vaccination season; it is available online at

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Q: We are unsure about when to start our influenza vaccination promotion, and when to ideally vaccinate our patients. Does protection from seasonal influenza vaccine decline or wane during the influenza season? Should I wait until later in the year to vaccinate my elderly or medically frail patients?  

A: No one can predict when influenza disease will peak in a given season. Local outbreaks can begin as early as October, but CDC reports that 75% of influenza seasons peak in January or later. 
Several studies have reported decreases in vaccine effectiveness over the influenza season. However, waning effects have not been observed consistently across age groups, virus subtypes, and seasons. While delaying vaccination might permit greater immunity later in the season, deferral could result in missed opportunities to vaccinate, as well as difficulties in vaccinating a large number of people within a more limited time period.
Balancing issues regarding the difficulty in predicting when influenza outbreaks will occur with concerns about waning immunity during the flu season, especially in older adults, CDC recommends that vaccination should be offered by the end of October. Vaccination efforts should continue as long as influenza viruses are circulating. 
Children age 6 months to 8 years without two prior doses of flu vaccine need 2 doses. They should get their first influenza vaccination as soon as vaccine becomes available; the minimum interval for the second dose is 28 days. 
For people that need only 1 dose, early vaccination (i.e., July and August) can result in reduced immune protection towards the end of the influenza season, particularly for older adults.   
For people who have already been fully vaccinated, revaccination later in the season is not recommended.

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Q: Which influenza vaccines can we give to children?

A: Four injectable inactivated influenza vaccines are now approved by FDA for children as young as 6 months:

  • Fluzone Quadrivalent (Sanofi Pasteur),
  • FluLaval Quadrivalent (GSK),
  • Fluarix Quadrivalent (GSK), and
  • Afluria Quadrivalent (Seqirus). 

Inactivated cell culture-based influenza vaccine, Flucelvax Quadrivalent (Seqirus) is approved for people age 4 years and older.
The nasal spray live attenuated influenza vaccine (LAIV, FluMist, AstraZeneca) is approved for healthy people age 2–49 years who are not pregnant. Information about all influenza vaccines available in the U.S., including product billing codes, is available in IAC's handout titled "Influenza Vaccine Products for the 2019–2020 Influenza Season" at Information on vaccine products for the U.S. is also available on CDC’s website at

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Q: Please provide details about the use of inactivated influenza vaccines in children younger than age 3 years.

A: Afluria Quadrivalent (Seqirus) dosing is 0.25 mL given IM for children age 6–35 months and 0.5 mL for children age 3 years and older.
The dosing for FluLaval Quadrivalent (GSK) and Fluarix Quadrivalent (GSK) vaccines is 0.5 mL for children age 6 months and older.
For Fluzone Quadrivalent (Sanofi), either 0.25 mL or 0.5 mL doses can be given to children age 6–35 months. For children age 3 years and older, the dose is 0.5 mL.
Flucelvax Quadrivalent (Seqirus) is recommended beginning at age 4 years at 0.5 mL dose, but cannot be used for children younger than age 4 years. 

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Q:  Which children younger than age 9 years will need 2 doses of influenza vaccine in this influenza season?

A: Children age 6 months through 8 years should receive a second dose 4 weeks or more after the first dose 1) if they are receiving influenza vaccine for the first time, 2) if they did not receive a total of at least two prior doses of trivalent or quadrivalent influenza vaccine before July 1 of the current year, or 3) if their vaccination history is unknown. The two doses need not have been received during the same season or consecutive seasons. A 9-year-old should receive a dose of influenza vaccine if they turned 9 years during the current season. IAC's handout titled "Guide for Determining the Number of Doses of Influenza Vaccine to Give to Children Ages 6 Months Through 8 Years" provides guidance on this issue; it is available at

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Q:  Do any children age 9 years and older need two total doses during an influenza season?

A: Yes. A 9-year-old should receive a dose of influenza vaccine if they turned 9 years old during the current season and already received one dose during the current season when they were 8 years old, AND they did not receive a total of at least two prior doses of trivalent or quadrivalent influenza vaccine before July 1 of the current year, or if their vaccination history is unknown before July 1 of the current year. 

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Q: Can a child age 6–35 months who needs 2 doses of influenza vaccine this season receive a combination of Afluria, Fluzone, FluLaval, Fluarix, or FluMist vaccine?

A: Yes. Afluria (0.25 mL per dose), Fluzone (0.25 mL or 0.5 mL per dose), FluLaval (0.5 mL dose), and Fluarix (0.5 mL dose) are approved by the FDA for use in children age 6–35 months. If a child is age 2 years or older, FluMist may also be used when age and health condition are appropriate.

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Q: If a child receives Fluzone Quadrivalent vaccine (0.25 mL) at age 34 or 35 months for the first time and then returns for the second dose at age 37 months, should we give another 0.25 mL dose of Fluzone Quadrivalent or should we give the 0.5 mL dose that is indicated for age 3 years and older?

A: The child should always receive the dose appropriate for his or her age at the time of the clinic visit; at age 37 months that would be 0.5 mL.

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Q: Is influenza vaccine recommended for pregnant women?

A: Yes. It is especially important to vaccinate pregnant women because of their increased risk for influenza-related complications and their baby’s increased risk of influenza-related illness and hospitalizations during the first 6 months of life.
Influenza vaccination during pregnancy reduces mothers’ risk of influenza illness, preterm labor, and their infants’ risk of influenza and influenza-related hospitalization in the first 6 months of life.
Most studies of influenza vaccination in pregnant women have administered vaccine in the second or third trimester using inactivated influenza vaccine.
Vaccination can occur in any trimester, including the first. Only inactivated vaccine or recombinant influenza can be given to pregnant women. LAIV should not be used in pregnant women.

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Q: If a patient was vaccinated earlier in the influenza season and later becomes pregnant during the same season, should she be revaccinated due to her pregnancy?

A: No. The Advisory Committee on Immunization Practices (ACIP) does not recommend more than one dose of influenza vaccine per season, except for certain children being vaccinated for the first time.

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Q: Please tell me about Fluad, one of the influenza vaccines for people age 65 years and older.

A: In November 2015, FDA licensed Fluad (Seqirus), a trivalent, MF59-adjuvanted inactivated influenza vaccine, for people age 65 years and older. Fluad is the first adjuvanted influenza vaccine marketed in the U.S. An adjuvant is a substance added to a vaccine to increase its immunogenicity. The MF59 adjuvant is based on squalene, an oil that occurs naturally in many plants and animals. Fluad has been used in Europe since 1997 and is approved in 38 other countries. In contrast to Fluzone High-Dose (Sanofi Pasteur), Fluad is a standard-dose vaccine, containing 15 mcg of hemagglutinin per virus per dose (total of 45 mcg). In a small observational study among adults age 65 years and older, Fluad was about 63% more effective than unadjuvanted trivalent IIV. ACIP has not stated a preference for Fluad (or Fluzone HD or Flublok, Sanofi Pasteur) over standard dose IIV for people age 65 years and older.

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Q: Sometimes patients age 65 years and older who have received the standard-dose influenza vaccine hear about the high-dose (Fluzone High-Dose) or adjuvanted vaccine (Fluad) and want to receive that, too. Is this okay to administer?

A: No. ACIP does not recommend that anyone receive more than one dose of influenza vaccine in a season, except for certain children age 6 months through 8 years for whom two doses are recommended.

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Q: Which healthcare personnel should be vaccinated against influenza?

A: It is important to vaccinate ALL hospital and outpatient-care personnel, especially those that have direct contact with patients. In addition to physicians and nurses, vaccination in a hospital setting also includes full-time and part-time employees in radiology, laboratories, pharmacy, human resources, facilities management (housekeeping), food services, and laundry. Vaccinate volunteers as well. Others who should be vaccinated are emergency response workers, employees of nursing homes and assisted living programs, and providers of home care. 

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Q: What is the preferred anatomic site for administration of inactivated influenza vaccine (IIV) and recombinant influenza vaccine?

A: IIV should be administered in the anterolateral thigh muscle of an infant or young child. IIV and RIV (FDA-approved only for people age 18 years and older) should be administered in the deltoid muscle of an older child, adolescent, or adult. The anterolateral thigh muscle can also be used for an older child, adolescent, or adult if necessary. It is critical that intramuscular influenza vaccine be injected into a muscle.
Influenza vaccination season is an opportune time to review proper intramuscular injection techniques with your staff. IAC has prepared a handout on how to administer intramuscular vaccine injections (available at that can be used as a staff training tool.
CDC has created an excellent training video on how to administer intramuscular vaccine injections. It is available for viewing at

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Q:  For whom is inactivated influenza vaccine contraindicated?

A: People who have experienced a severe allergic reaction to a prior dose of influenza vaccine, or who are known to have a severe allergy to a vaccine component (except egg) should not be vaccinated.
Precautions to vaccination include moderate or severe acute illness, and history of Guillain-Barré syndrome within 6 weeks of a dose of influenza vaccine.

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Q:  What are the contraindications for live attenuated influenza vaccine (LAIV, FluMist)?

A: Contraindications to LAIV are: 

  • history of a severe allergic reaction to a vaccine component (except egg—see next question) or after a previous dose of any influenza vaccine;
  • concomitant aspirin- or salicylate-containing therapy in children and adolescents because of the risk of Reye syndrome;
  • children age 2 through 4 years who have received a diagnosis of asthma or whose parents or caregivers report that a healthcare provider has told them during the preceding 12 months that their child had wheezing or asthma or whose medical record indicates a wheezing episode during the preceding 12 months;
  • immunosuppression due to any cause, including medications or HIV infection;
  • close contacts and caregivers of severely immunosuppressed people who require a protected environment (e.g. reverse isolation in a hospital);
  • pregnancy;
  • receipt of influenza antiviral medication within the previous 48 hours. 

Precautions to LAIV are: 

  • moderate or severe acute illness with or without fever;
  • history of Guillain-Barré syndrome within 6 weeks of receipt of influenza vaccine;
  • asthma in a person age 5 years and older;
  • underlying medical conditions that might predispose to complications after influenza virus infection, such as chronic pulmonary, cardiovascular (except isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders including diabetes mellitus.

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Q:  What is the latest ACIP guidance on influenza vaccination and egg allergy?

A: ACIP recommends that people with a history of egg allergy who have experienced only hives after exposure to egg should receive influenza vaccine without specific precautions (except a 15-minute observation period for syncope). Any age-appropriate vaccine (IIV, RIV or LAIV) may be used. People who report having had an anaphylactic reaction to egg (more severe than hives) may also receive any age-appropriate influenza vaccine (IIV, RIV or LAIV). The vaccine for those individuals should be administered in a medical setting (such as a physician office or health department clinic). Vaccine administration should be supervised by a healthcare provider who is able to recognize and manage severe allergic conditions. Although not specifically recommended by ACIP, providers may prefer an egg-free inactivated vaccine (Flucelvax Quadrivalent, Seqirus, licensed for people age 4 years and older) or recombinant vaccine (Flublok; Sanofi Pasteur, licensed for people age 18 years and older) with severe egg allergy.
A previous severe allergic reaction to influenza vaccine, regardless of the component suspected to be responsible for the reaction, is a contraindication to future receipt of the vaccine. For a complete list of vaccine components (i.e., excipients and culture media) used in the production of the vaccine, check the package insert (available at or go to
For more details about giving influenza vaccine to people with a history of egg allergy, see the ACIP guidance at You also may find the IAC handout "Influenza Vaccination of People with a History of Egg Allergy" helpful (see

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Q:  Is the Influenza Vaccine Information Statement (VIS) changing for the 2019–2020 influenza season?

A: Yes. Both the inactivated and the live influenza vaccine VISs (dated August 15, 2019) were updated for the 2019–2020 influenza season. 

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Q:  When administering influenza vaccine, is giving patients a VIS mandatory or is it only "recommended"?

A: Providing patients with an influenza Vaccine Information Statement (VIS) is mandatory under the National Childhood Vaccine Injury Act of 1986. The VIS must be given to all adults as well as to parents or guardians of children prior to vaccination. Two VISs are available, one for live attenuated influenza vaccine (LAIV) and one for inactivated influenza vaccine (IIV). Each can be found at, along with many translations.

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How to submit a question to Ask the Experts

IAC works with CDC to compile new Ask the Experts Q&As for our publications based on commonly asked questions. We also consider the need to provide information about new vaccines and recommendations. Most of the questions are thus a composite of several inquiries.

You can email your question about vaccines or immunization to IAC at

As we receive hundreds of emails each month, we cannot promise that we will print your specific question in our Ask the Experts feature. However, you will get an answer.

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Please forward these Ask the Experts Q&As to your colleagues and ask them to subscribe to IAC Express.

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