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Ask the Experts: Influenza

Results (96)

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.

Last reviewed: September 10, 2023

While even healthy children and adults get severe influenza or die from influenza and its complications, the risk of severe influenza is higher for children younger than 5 years, adults 50 years and older, pregnant people, Alaska Natives and American Indians, and residents of nursing homes or other long-term care facilities. Medical conditions that increase a person’s risk of severe influenza include chronic pulmonary (including asthma), cardiovascular (excluding isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus); immunocompromising conditions due to any cause (including but not limited to immune suppression caused by medications or HIV); extreme obesity (body mass index of 40 or greater for adults); and the chronic use of aspirin- or salicylate-containing medications in children through age 18 (due to the risk of Reye syndrome after influenza infection).

More information about risk factors for severe influenza infection can be found at: www.cdc.gov/flu/highrisk/index.htm.

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

Yes. Both viruses can circulate at the same time, and a person can be infected with both viruses at the same time. Illnesses experienced by people co-infected with influenza and SARS-CoV-2 are more likely to be severe compared with those infected with only SARS-CoV-2 or influenza alone. The extent to which SARS-CoV-2 and influenza viruses will co-circulate during the upcoming 2023–24 fall and winter respiratory virus season is unknown.

Last reviewed: September 10, 2023

Information regarding influenza surveillance is available year-round from CDC at www.cdc.gov/flu/weekly/fluactivitysurv.htm. The full FluView surveillance report is published each Friday afternoon from October through mid-May and an abbreviated FluView report is published Mid-May through September. In addition, periodic updates about influenza are published in MMWR.

State and local health departments should be consulted regarding local availability of influenza vaccine, access to vaccination programs, information about state or local influenza activity, and for reporting influenza outbreaks and receiving advice regarding their control.

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

ACIP recommends annual vaccination for all people ages 6 months and older who do not have a contraindication to influenza vaccination.

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

Vaccine viruses differ by the type of vaccine (egg-based or non-egg-based), but they protect against the same strains of circulating viruses.

For the 2023–24 season, U.S. egg-based influenza vaccines (vaccines other than ccIIV4 and RIV4) will contain hemagglutinin (HA) derived from:
• an influenza A/Victoria/4897/2022(H1N1)pdm09-like virus,
• an influenza A/Darwin/9/2021 (H3N2)-like virus,
• an influenza B/Austria/1359417/2021 (Victoria lineage)-like virus, and
• an influenza B/Phuket/3073/2013(Yamagata lineage)-like virus.

For the 2023–24 season, U.S. cell culture–based inactivated (ccIIV4) and recombinant (RIV4) influenza vaccines will contain HA derived from:
• an influenza A/Wisconsin/67/2022(H1N1)pdm09-like virus,
• an influenza A/Darwin/6/2021 (H3N2)-like virus,
• an influenza B/Austria/1359417/2021 (Victoria lineage)-like virus, and
• an influenza B/Phuket/3073/2013 (Yamagata lineage)-like virus.

Last reviewed: September 10, 2023

Four egg-based quadrivalent inactivated influenza vaccines (IIV4s) and one cell-based quadrivalent inactivated influenza vaccine (ccIIV4), all given as intramuscular (IM) injections, are available for children age 6 months and older:

  • Afluria Quadrivalent (CSL Seqirus): 0.25 mL/dose for age 6 through 35 months; 0.5 mL/dose for age 3 years and older
  • Fluarix Quadrivalent (GSK): 0.5 mL/dose for age 6 months and older
  • FluLaval Quadrivalent (GSK): 0.5 mL/dose for age 6 months and older
  • Fluzone Quadrivalent (Sanofi): 0.25 mL or 0.5 mL per dose for age 6 through 35 months; 0.5 mL/dose age 3 years and older
  • Flucelvax Quadrivalent (ccIIV4, CSL Seqirus) cell-based (no egg antigen): 0.5 mL/dose (IM) for age 6 months and older

FluMist Quadrivalent (LAIV4, AstraZeneca) egg-based live nasal spray vaccine is 0.2 mL (intranasal, 0.1 mL in each nostril) for healthy, non-pregnant children and teens age 2 years and older.

Last reviewed: September 10, 2023

Four egg-based quadrivalent standard dose IIV vaccines (SD-IIV4s), and one cell-based quadrivalent standard dose inactivated vaccine (ccIIV4), all given as intramuscular (IM) injection may be used in adults age 18 or older:

  • Afluria Quadrivalent (CSL Seqirus): 0.5 mL/dose
  • Fluarix Quadrivalent (GSK): 0.5 mL/dose
  • FluLaval Quadrivalent (GSK): 0.5 mL/dose
  • Fluzone Quadrivalent (Sanofi): 0.5 mL/dose
  • Flucelvax Quadrivalent (ccIIV4, CSL Seqirus) cell-based (no egg antigen): 0.5 mL/dose (IM) for adults age 18 or older

Additional products for adults:

FluMist Quadrivalent (LAIV4, AstraZeneca): egg-based, live nasal spray vaccine: 0.2 mL (given intranasally, 0.1 mL in each nostril) for healthy, non-pregnant adults through age 49 years.

Flublok Quadrivalent (RIV4, Sanofi): recombinant, egg-free vaccine: 0.5 mL/dose (given IM) for adults age 18 or older (one of three preferred product options for adults age 65 and older).

Fluzone High-Dose Quadrivalent (egg-based HD-IIV4, Sanofi): 0.7 mL (given IM), for adults age 65 years and older (one of three preferred product options for adults age 65 and older).

Fluad Quadrivalent (egg-based aIIV4 with MF59 adjuvant, CSL Seqirus): 0.5 mL (given IM), for adults age 65 years and older (one of three preferred product options for adults age 65 and older).

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

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 8 years old 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.

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

CDC and ACIP make no recommendation for revaccination later in the season of people who have been fully vaccinated for the season, regardless of when the current season vaccine was received.

Last reviewed: September 10, 2023

Peak influenza activity generally occurs in the Northern Hemisphere during December through March, most frequently in January or February. Providers should continue vaccinating patients through spring, as long as there is continued circulation of influenza viruses and they have unexpired vaccine in stock and unvaccinated patients in their office.

Because influenza occurs in many areas of the world during April through September, vaccine should be given to travelers who missed vaccination in the preceding fall and winter. Another late season use of vaccine is for children younger than age 9 years who needed 2 doses of vaccine but failed to get their second dose. For each of these situations, vaccine can be given through the month of June since most injectable influenza vaccine has a June 30 expiration date.

Last reviewed: September 10, 2023

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.

Last reviewed: September 10, 2023

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.

Healthcare providers should vaccinate any person who failed to get vaccinated in the previous vaccination season and who wants to reduce their risk of getting influenza during their upcoming travel, particularly if they are at high risk for influenza-related complications. This includes people who are traveling to the tropics, traveling with organized tourist groups at any time of year, or traveling to the Southern Hemisphere during April–September.

Last reviewed: September 10, 2023

There should be a minimum of 4 weeks between the doses in such situations.

Last reviewed: September 10, 2023

This page was updated on .

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