As an additional service to IZ Express readers, we periodically publish special editions such as this one, providing you with new and updated Ask the Experts questions and answers from Immunize.org experts. This issue includes 14 Q&As about influenza vaccination based on recently updated ACIP recommendations.
To find the full set of Immunize.org's Ask the Experts influenza vaccination Q&As, visit www.immunize.org/askexperts/experts_inf.asp.
You can find all of these questions and answers, plus more than 1,200 others about vaccines and vaccine administration, on our "Ask the Experts" main page at www.immunize.org/askexperts.
Immunize.org's team of experts includes Kelly L. Moore, MD, MPH (team lead), Carolyn B. Bridges, MD, FACP, and Iyabode Beysolow, MD, MPH.
Influenza Vaccination for the 2023–24 Season
Q: Please summarize what's new in the 2023–24 influenza vaccine recommendations.
A: Yearly influenza vaccination continues to be recommended for everyone age 6 months and older. All available influenza vaccines in the United States continue to be quadrivalent (containing two influenza A and two influenza B strains). The changes in the CDC's published Advisory Committee on Immunization Practices (ACIP) recommendations for influenza vaccination in 2023–2024 are summarized below:
- The 2023–24 vaccines include a new influenza A(H1N1)pdm09 component and influenza B/Victoria lineage virus vaccine antigens
- ACIP affirmed that everyone age 6 months and older who has an egg allergy should receive influenza vaccine. Any influenza vaccine (egg based or non-egg based) that is otherwise appropriate for the recipient’s age and health status may be used. ACIP updated its recommendation to state that egg allergy alone necessitates no additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine, regardless of severity of previous reaction to egg. All vaccines should be administered in settings in which personnel and equipment needed for rapid recognition and treatment of acute hypersensitivity reactions are available.
The current ACIP recommendations for influenza vaccination are available here: www.cdc.gov/mmwr/volumes/72/rr/pdfs/rr7202a1-H.pdf.
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Q: How serious a problem is influenza in the United States?
A: Influenza is the second most frequent cause of death from a vaccine-preventable disease in the United States after COVID-19. Rates of infection from seasonal influenza are highest among children, but the risks for complications, hospitalizations, and deaths are higher among adults age 65 years and older, children younger than 5 years, pregnant individuals, and people of any age who have medical conditions that place them at increased risk for complications from influenza.
From the 2010–11 through the 2022–23 seasons (excluding 2020–2021, when COVID-19 control measures resulted in almost no influenza activity), the annual influenza-related disease burden has varied from approximately 9 to 41 million illnesses, 4 to 21 million medical visits, 140,000 to 810,000 hospitalizations and 12,000 to 61,000 deaths per year, including an average of 129 pediatric deaths reported to CDC (range 37–199) each year. While the 2020–21 and 2021–22 seasons’ disease burden was substantially limited as a result of measures taken by many people to reduce the transmission of COVID-19, such as wearing face masks in public and limiting interactions with other people, influenza activity returned to pre-pandemic levels in 2022–23. For additional information about disease burden from CDC, see www.cdc.gov/flu/about/burden/index.html.
Q: What kind of influenza activity might be expected for 2023–24 influenza season?
A: The timing and severity of influenza seasons are always unpredictable. Influenza viruses circulated at very low levels while measures to prevent the spread of COVID-19 were widely adopted, including social distancing, mask wearing, and reduction in travel. As the use of these COVID-19 mitigation measures decreased, there was an increase in the circulation of influenza and other respiratory viruses. Current information on influenza virus circulation can be found at www.cdc.gov/flu/weekly/index.htm.
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Q: Who is recommended to be vaccinated against influenza?
A: ACIP recommends annual vaccination for all people age 6 months and older who do not have a contraindication to influenza vaccination.
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Q: Which influenza vaccines will be available during the 2023–24 influenza season?
A: Multiple manufacturers are producing quadrivalent influenza vaccine for the U.S. market for the 2023–24 season. Inactivated influenza vaccines (IIV4) will be produced using egg-based, cell culture-based, and recombinant technologies. Live attenuated nasal spray vaccine will also be available.
Not all influenza vaccines are licensed for all age groups.
Immunize.org has a 1-page printable document that summarizes each of the products available for the current influenza vaccination season at www.immunize.org/catg.d/p4072.pdf.
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Q: Are any of the available flu vaccines recommended over others?
A: For people age 6 months through 64 years, CDC recommends any available age-appropriate vaccine product.
For adults age 65 years and older, three flu vaccines are preferentially recommended: Fluzone High-Dose Quadrivalent, Flublok Quadrivalent recombinant, and Fluad Quadrivalent adjuvanted flu vaccines. In June 2022, ACIP concluded that these three vaccines are potentially more effective than standard dose, unadjuvanted flu vaccines. However, if none of the three vaccines are available, people age 65 years and older should get any other age-appropriate flu vaccine.
Review the full explanation for the ACIP decision in the 2022 published ACIP recommendations for influenza vaccination: www.cdc.gov/mmwr/volumes/71/rr/pdfs/rr7101a1-H.pdf.
Q: When does CDC recommend starting influenza vaccination?
A: For most people who need only 1 dose of influenza vaccine, vaccination should ideally be offered in September and October. For people not vaccinated by the end of October, vaccination efforts should continue as long as influenza viruses are circulating and unexpired vaccine is available.
Vaccination in July and August should be avoided for most groups unless there is concern that vaccination later in the season might not be possible. Early vaccination has been associated with waning of vaccine-induced immunity and decreased vaccine effectiveness before the end of the influenza season, particularly among older adults.
Vaccination in July and August may be considered for people in their third trimester of pregnancy, to allow time for protective maternal antibodies to transfer to the fetus, providing protection during early infancy. Children younger than age 9 years who need two doses of vaccine this season should receive their first dose as soon as possible so that they can get their second dose before the end of October. Children who need only one dose can be considered for vaccination in July or August.
Q: May influenza vaccines be given at the same time as other vaccines, including COVID-19 vaccines?
A: CDC's clinical guidance for the use of COVID-19 vaccines states that any vaccine may be given on the same day or any day before or after COVID-19 vaccination, at a different anatomic site. According to the CDC's "General Best Practice Guidelines for Immunization", simultaneously administering all vaccines for which a person is eligible at the time of a visit increases the probability that a person will be fully vaccinated by the appropriate time.
IIV4 and RIV4 can be administered without regard to the timing of other live or inactivated vaccines. Injectable vaccines should be administered in separate anatomic sites when given on the same day.
LAIV4 may be given on the same day as any other live or inactivated vaccines. However, if two live vaccines are not given on the same day, they should be separated by at least 4 weeks.
There are now several vaccines containing nonaluminum adjuvants recommended for adults (including Shingrix [zoster], Heplisav-B [HepB], Arexvy [RSV] and Fluad [aIIV4, influenza]). Because of the limited data on the safety of simultaneous administration of two or more vaccines containing nonaluminum adjuvants and the availability of nonadjuvanted influenza vaccine options, ACIP advises that selection of a nonadjuvanted influenza vaccine may be considered in situations in which influenza vaccine and another vaccine containing a nonaluminum adjuvant are to be administered at the same visit. However, influenza vaccination should not be delayed if a specific vaccine is not available.
Q: May influenza vaccines be given at the same time as RSV vaccine?
A: While CDC states that it is acceptable to coadminister influenza and RSV vaccines, there are issues that should be considered before deciding to coadminister these vaccines to a specific patient. Data informing simultaneous administration with influenza vaccines is limited and evolving. Data on coadministration of RSV and influenza vaccines showed that antibody titers were somewhat lower with coadministration; however, the clinical significance of this is unknown. In addition, administering RSV vaccine with one or more other vaccines at the same visit might increase local or systemic reactogenicity. Data are available for coadministration of RSV and influenza vaccines, and evidence is mixed regarding increased reactogenicity.
ACIP advises that when deciding whether to coadminister other vaccines with an RSV vaccine, consider whether the patient is up to date with currently recommended vaccines, the feasibility of the patient returning for additional vaccine doses, risk for acquiring vaccine-preventable disease, vaccine reactogenicity profiles, and patient preferences.
Additional considerations for coadministration of influenza and other vaccines are available in the 2023 ACIP RSV vaccine recommendations for older adults, page 798: www.cdc.gov/mmwr/volumes/72/wr/pdfs/mm7229a4-H.pdf.
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 have not received a total of at least two doses of any seasonal influenza vaccine before July 1 of the current year, or 3) if their vaccination history is unknown. The two previous doses need not have been received during the same season or consecutive seasons.
Children who are age 8 years and are recommended to receive two doses during the current season but who have a 9th birthday during the current season before receiving dose 2 should still receive dose 2.
Immunize.org's handout titled "Guide for Determining the Number of Doses of Influenza Vaccine to Give to Children Age 6 Months through 8 Years" provides additional guidance on this issue; it is available at www.immunize.org/catg.d/p3093.pdf.
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Q: What is the latest ACIP guidance on influenza vaccination and egg allergy?
A: The 2023 influenza ACIP recommendations state that everyone age 6 months or older with egg allergy should receive an influenza vaccine. Any influenza vaccine (egg based or non-egg based) appropriate for the person’s age and health status can be used.
Egg allergy alone does not require any additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine. All vaccines should be administered in settings in which personnel and equipment needed for rapid recognition and treatment of acute hypersensitivity reactions are available.
A person who has had a previous severe allergic reaction to an influenza vaccine has a contraindication to future receipt of that vaccine. For a complete list of vaccine components (including excipients and culture media) used in the production of the vaccine, check the package insert (available at www.immunize.org/fda) or go to www.cdc.gov/vaccines/pubs/pinkbook/downloads/appendices/B/excipient-table-2.pdf.
For more on the evidence and rationale supporting the change in recommendations regarding influenza vaccination and egg allergy, see the ACIP guidance at www.cdc.gov/mmwr/volumes/72/rr/pdfs/rr7202a1-H.pdf.
Q: What are contraindications and precautions for inactivated or recombinant influenza vaccines?
A: Contraindications to egg-based inactivated influenza vaccines (IIV) are a severe allergic reaction to a prior dose of any influenza vaccine (any egg-based IIV, ccIIV, RIV, or LAIV of any valency) or a severe allergy to an influenza vaccine component (except egg). ACIP recommends that people with egg allergy of any severity may receive any influenza vaccine appropriate for their age and health status.
Precautions to egg-based IIV include moderate or severe acute illness, and history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine.
Contraindications to ccIIV4 are a history of a severe allergic reaction or any component of ccIIV4.
Precautions to ccIIV4 are moderate or severe acute illness, a history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine, and a history of a severe allergic reaction to a previous dose of any other influenza vaccine (e.g., any egg-based IIV, RIV, or LAIV).
Contraindications to RIV4 are a history of a severe allergic reaction or any component of RIV4.
Precautions to RIV4 are moderate or severe acute illness, a history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine, and a history of a severe allergic reaction to a previous dose of any other influenza vaccine (e.g., any egg-based IIV, ccIIV, or LAIV).
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Q: What are the contraindications and precautions for FluMist Quadrivalent (LAIV4)?
A: Contraindications are:
- a history of severe allergic reaction to a vaccine component (except egg) or after a previous dose of any influenza vaccine (people with egg allergy of any severity may receive LAIV if it is otherwise appropriate for their age and health status)
- 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
- cerebral spinal fluid (CSF) leak, cochlear implant, or anatomic asplenia or functional asplenia (e.g., due to sickle cell anemia)
- close contacts and caregivers of severely immunosuppressed people who require a protected environment (e.g., reverse isolation in a hospital)
- receipt of influenza antiviral medication within the previous 48 hours (oseltamivir or zanamivir), previous 5 days (peramivir), or previous 17 days (baloxavir)
- moderate or severe acute illness with or without fever (defer)
- history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine
- asthma in a person age 5 years or 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 most up-to-date Influenza Vaccine Information Statement (VIS) for the 2023–24 influenza season?
A: Both the inactivated and recombinant influenza vaccine VIS and the live influenza vaccine VIS were updated on August 6, 2021. These VISs and translations in multiple languages are available here: www.immunize.org/vis.
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