Ask the Experts: Influenza

Results (96)

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 by the 2022–23 season. For additional information about disease burden from CDC, see www.cdc.gov/flu-burden/php/about/index.html.

Rates of infection from seasonal influenza are highest among children, but the risks for complications, hospitalizations, and deaths are highest among adults age 65 years and older.

Last reviewed: August 11, 2024

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: August 11, 2024

The timing and severity of influenza seasons are always unpredictable. Although influenza viruses circulated at very low levels while measures to prevent the spread of COVID-19 were widely adopted during the pandemic, the circulation of influenza viruses has returned to pre-pandemic patterns. Current information on influenza virus circulation can be found at www.cdc.gov/fluview/.

Last reviewed: August 11, 2024

Information regarding influenza surveillance is available year-round from CDC. For an overview and link to CDC’s influenza surveillance systems, visit www.cdc.gov/fluview/. CDC publishes updated information weekly. In addition, periodic updates about influenza are published in MMWR. CDC also publishes respiratory virus surveillance information that integrates influenza, COVID-19 and RSV at www.cdc.gov/respiratory-viruses/data/index.html.

State and local health departments should be consulted regarding local access to public health influenza vaccination programs and information about state or local influenza activity. Contact state or local health officials to report influenza outbreaks and for guidance in outbreak response.

Last reviewed: August 11, 2024

Yearly influenza vaccination continues to be recommended for everyone age 6 months and older. Changes relevant to clinical practice in the CDC’s published ACIP recommendations for influenza vaccination in the 2024-25 season are summarized below:

  • ACIP now recommends high-dose inactivated influenza vaccine (HD-IIV) or adjuvanted inactivated (aIIV) influenza vaccine (each licensed by FDA for people age 65 years or older) as acceptable options for influenza vaccination of solid organ transplant recipients age 18 through 64 years who are on immunosuppressive medication regimens. There is no preference for aIIV or HD-IIV over any other age-appropriate inactivated or recombinant influenza vaccine in this group.
  • The HD-IIV vaccine, which is now trivalent, is given at a dose of 0.5 mL (the previous dose for quadrivalent HD-IIV was 0.7 mL).
  • 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/acip-recs/hcp/vaccine-specific/flu.html.

Last reviewed: August 11, 2024

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

Last reviewed: August 11, 2024

Multiple manufacturers are producing inactivated, recombinant, and live attenuated influenza vaccines for the U.S. market for the 2024-25 season. All vaccines are trivalent (containing two influenza A and one influenza B virus vaccine antigen).

Immunize.org offers a 1-page printable document that summarizes each of the products available for the current influenza vaccination season: www.immunize.org/catg.d/p4072.pdf.

Last reviewed: August 11, 2024

The 2024-25 vaccines are all trivalent (containing two influenza A and one influenza B strains). The B/Yamagata virus vaccine antigens are no longer included in influenza vaccines because B/Yamagata viruses have not been detected globally since March 2020.

The 2024-25 vaccines include a new influenza A(H3N2) component.

Egg-based influenza vaccines include:

  • an A/Victoria/4897/2022 (H1N1)pdm09-like virus;
  • an A/Thailand/8/2022 (H3N2)-like virus; and,
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

Cell culture-based or recombinant vaccines include:

  • an A/Wisconsin/67/2022 (H1N1)pdm09-like virus;
  • an A/Massachusetts/18/2022 (H3N2)-like virus; and,
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Last reviewed: August 11, 2024

All nine 2024-25 influenza vaccines approved for adults are trivalent, containing two influenza A strains and one influenza B strain.

There are five injectable inactivated influenza vaccine (IIV) options approved for use in all adults age 18 years or older. Four egg-based standard dose IIV vaccines (SD-IIVs) and one cell culture-based one (ccIIV) are available, all given as an intramuscular (IM) injection:

  • Afluria (CSL Seqirus): 0.5 mL/dose
  • Fluarix (GSK): 0.5 mL/dose
  • FluLaval (GSK): 0.5 mL/dose
  • Fluzone (Sanofi): 0.5 mL/dose
  • Flucelvax (ccIIV, CSL Seqirus) cell culture-based (no egg antigen): 0.5 mL/dose

One egg-based live attenuated nasal spray vaccine, FluMist (LAIV, AstraZeneca), is an option for healthy, non-pregnant adults through age 49 years: 0.2 mL (given intranasally, 0.1 mL in each nostril).

Three injectable vaccines, all given IM, are ACIP-preferred options for adults age 65 years or older:

  • Recombinant influenza vaccine, Flublok (RIV, Sanofi): 0.5 mL/dose, licensed for use in adults age 18 or older
  • Fluzone High-Dose (egg-based HD-IIV, Sanofi): 0.5 mL/dose, licensed for adults age 65 years and older
  • Fluad (egg-based aIIV with MF59 adjuvant, CSL Seqirus): 0.5 mL/dose, licensed for adults age 65 years and older

Although licensed by FDA for use in adults age 65 years or older, ACIP also recommends off-label use of Fluzone HD or Fluad as acceptable options for influenza vaccination of solid organ transplant recipients age 18 through 64 years who are on immunosuppressive medication regimens, without a preference over other age-appropriate IIVs or RIV.

Last reviewed: August 11, 2024

For people age 6 months through 64 years, CDC recommends any available age-appropriate influenza vaccine product.

For adults age 65 years and older, three influenza vaccines are preferentially recommended: Fluzone High-Dose (HD-IIV, Sanofi), Flublok recombinant (RIV, Sanofi), and Fluad adjuvanted (aIIV, CSL Seqirus). 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 products are available, people age 65 years and older should get any other age-appropriate influenza vaccine.

Review the full explanation for the ACIP decision to prefer these products in this age group in the 2022 ACIP recommendations for influenza vaccination: www.cdc.gov/mmwr/volumes/71/rr/pdfs/rr7101a1-H.pdf.

ACIP recommends that solid organ transplant recipients (SOTRs) age 18 years through 64 years have the option of receiving HD-IIV or aIIV, both of which are licensed for people age 65 years or older. However, HD-IIV and aIIV are not preferentially recommended over age-appropriate influenza vaccine products for SOTRs.

Last reviewed: September 5, 2024


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Last reviewed: August 11, 2024

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: August 11, 2024


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Last reviewed: August 11, 2024

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: August 11, 2024

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: August 11, 2024


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Last reviewed: March 28, 2023

Yes, influenza vaccines may be coadministered with other recommended vaccines.

The live attenuated nasal spray influenza vaccine (FluMist, LAIV) 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 [aIIV, influenza]). Because of the limited data on the safety or reactogenicity of simultaneous administration of two or more vaccines containing nonaluminum adjuvants and the availability of nonadjuvanted influenza vaccine options, ACIP advises considering a nonadjuvanted influenza vaccine in situations in which influenza vaccine and another vaccine containing a nonaluminum adjuvant are due at the same visit. However, influenza vaccination should not be delayed if a specific vaccine is not available.

Last reviewed: August 11, 2024


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Last reviewed: August 11, 2024

Yes, coadministration of influenza and RSV vaccines at the same visit is acceptable. Evidence is limited and mixed concerning the effects of coadministration on antibody titers or on any increase in side effects (reactogenicity) experienced by the recipient following coadministration. CDC has provided the details of available information in its guidance on RSV vaccination of older adults: www.cdc.gov/vaccines/vpd/rsv/hcp/older-adults.html#administration-other-vaxs.

CDC 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, their risk for acquiring vaccine-preventable disease, vaccine reactogenicity profiles, and patient preferences.

Last reviewed: August 11, 2024

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: August 11, 2024

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

Last reviewed: August 11, 2024

Because more than one type or subtype of influenza virus can circulate in any given influenza season, providers should offer influenza vaccination to unvaccinated people throughout the influenza season, including people who may have had an influenza illness already in the season.

Last reviewed: August 11, 2024

Protection from influenza vaccine wanes after vaccination (the amount of protection and the speed of waning varies by strain and by recipient age), but generally persists for at least 5–6 months.

Last reviewed: August 11, 2024

First, injectable influenza vaccines cannot cause influenza because they contain only parts of the virus. The live attenuated nasal spray vaccine is modified so that it cannot cause influenza because it cannot replicate at human body temperature. Fewer than 1% of vaccinated people might develop flu-like symptoms, such as mild fever and muscle aches, after vaccination. These vaccine side effects are not the same as having influenza, but people may confuse the side effects with illness.

Other reasons a person might have had influenza illness or an illness that they thought might be “the flu” after vaccination include:

  • Protective immunity doesn’t develop until 1–2 weeks after vaccination. Some people who get vaccinated after influenza viruses are already circulating may be infected with influenza before the vaccination can stimulate protective immunity.
  • For many people, “the flu” is any illness with fever, cold symptoms or gastrointestinal symptoms. If they get any viral illness, they may blame it on influenza vaccine or think they got “the flu” despite being vaccinated. Influenza vaccine only protects against specific influenza viruses, not all viruses.
  • Vaccinated people can get influenza illness despite vaccination. Influenza vaccination is our best available protection against influenza disease; however, vaccination reduces the risk of infection, it does not prevent all infections.

Vaccine effectiveness (VE) varies by age and by season, depending upon the circulating viruses. In most recent seasons, influenza vaccination has reduced the risk of illness by between roughly 40% and 60% in the vaccinated population (including all ages) during seasons when most circulating influenza viruses are well-matched to the vaccine. VE is generally lower for adults age 65 years and older. Influenza vaccination has also been shown to reduce influenza disease severity even if someone does get sick after vaccination, and vaccination reduces the risk of influenza hospitalization and deaths in children and adults. Influenza vaccination also reduces the risk of stroke and acute cardiac events, like heart attack and heart failure, among people with heart disease.

For more information on this topic, go to: www.cdc.gov/flu-vaccines-work/index.html.

Last reviewed: August 11, 2024

Giving patients 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) and recombinant vaccine (RIV). The IIV and RIV VIS and all of its translations are available here: www.immunize.org/vaccines/vis/influenza-inactivated/. The LAIV VIS and all of its translations are available here: www.immunize.org/vaccines/vis/influenza-live/. Current influenza vaccine VISs are dated August 6, 2021.

Immunize.org also offers a printable PDF document with QR codes for easy access to all of the IIV and RIV influenza vaccine VIS translations: www.immunize.org/wp-content/uploads/catg.d/p2092.pdf. Healthcare providers or recipients can scan the codes to access a digital copy of the translation on their mobile device.

Last reviewed: August 11, 2024

The most important factor in preventing outbreaks is annual vaccination of all residents and staff who work at facilities such as nursing homes, assisted living facilities, and other group living situations. Groups that should be targeted include physicians, nurses, and other personnel working or volunteering in hospitals and outpatient settings who have contact with high-risk patients in all age groups, and providers of home care to high-risk people (for example, visiting nurses, therapists, and volunteers).

Last reviewed: August 11, 2024

If a patient or family member cannot remember if the patient received influenza vaccine this season and no record is available, proceed with administering influenza vaccine, even if it might mean an extra dose is given. When a patient reports that they HAVE received influenza vaccine but does not have written documentation, ACIP states that in the specific case of influenza (and pneumococcal polysaccharide) vaccination, patient self-report of being vaccinated can be accepted as evidence of vaccination.

Last reviewed: August 11, 2024

FluMist (LAIV, AstraZeneca) is currently approved by FDA only for healthy non-pregnant people age 2 through 49 years.

Last reviewed: August 11, 2024

No. Giving FluMist (LAIV) is not considered an aerosol-generating procedure.

Last reviewed: August 11, 2024

The vaccine dose (0.2 mL) comes inside a special sprayer device. A plastic clip on the plunger divides the dose into two equal parts. The patient is seated in an upright position with head tilted back. Half of the contents of the sprayer (0.1 mL) is sprayed into each nostril.

Last reviewed: August 11, 2024

Yes, unless clinical judgment suggests nasal congestion is present that might keep the vaccine from making good contact with the nasopharyngeal mucosa. In that case, consider either deferring its use until the congestion resolves or using an appropriate alternative influenza vaccine, if available.

Last reviewed: August 11, 2024

Yes. Breastfeeding is not a contraindication for any routine vaccination including FluMist (LAIV).

Last reviewed: August 11, 2024

With rare exceptions, yes. Like other live vaccines, FluMist (LAIV) should not be administered to immunosuppressed people. ACIP has stated a preference for using injectable influenza vaccine for all close contacts of severely immunosuppressed individuals during those periods in which the immunosuppressed person requires care in a protective environment because of the theoretical risk that the live attenuated vaccine virus could be transmitted to the severely immunosuppressed individual and cause disease. Healthcare personnel or other people who have close contact with people with lesser degrees of immunosuppression (people who do not require a protective environment such as reverse isolation in a hospital setting) who are otherwise eligible for FluMist may receive it. No special precautions need to be taken by the vaccinated person.

Last reviewed: August 11, 2024

People should avoid contact with any person who is severely immunosuppressed for at least 7 days after receiving FluMist (LAIV). There are no restrictions on being in contact with any other patients.

Last reviewed: August 11, 2024

Asthma is a precaution, not a contraindication, for FluMist (LAIV) in people 5 years of age and older. FluMist is contraindicated for children 2 through 4 years old who have had a diagnosis of asthma or whose parents or caregivers report that a health care provider has told them during the preceding 12 months that their child had wheezing or asthma or whose medical record indicates a wheezing episode has occurred during the preceding 12 months.

Last reviewed: August 11, 2024

An antiviral drug active against influenza virus may reduce the effectiveness of FluMist by interfering with the vaccine viruses’ ability to replicate in the upper airway in order to produce protective immunity. To prevent interference, ACIP has recommended different intervals between the last dose of an antiviral medication and FluMist administration, based upon the half-life of the antiviral medication. The recommendations are as follows:

  • Oseltamivir or zanamivir: wait at least 48 hours after the last dose before administering FluMist
  • Peramivir: wait at least 5 days before administering FluMist
  • Baloxavir: wait at least 17 days before administering FluMist

If any influenza antiviral medication must be given within 14 days after FluMist administration, the patient should be revaccinated without delay with any age-appropriate injectable influenza vaccine. Inactivated influenza vaccines (IIVs) and recombinant influenza vaccine (RIV) may be administered at any time relative to antiviral medication.

Last reviewed: August 11, 2024

A half dose of FluMist (or any other vaccine) is a non-standard dose and generally should not be counted. If you were unable to give the second half of the vaccine on the same day, you will have to provide another full dose of influenza vaccine at another time. If you want to give FluMist again, you should wait four weeks because it is a live vaccine. Alternatively, you can give an injectable influenza vaccine any time after this partial dose.

Last reviewed: August 11, 2024

ACIP recommends annual influenza vaccination for all children age 6 months and older who do not have a contraindication to the vaccine.

Last reviewed: August 11, 2024

All six 2024-25 season influenza vaccines approved for children are trivalent, containing two influenza A strains and one influenza B strain.

There are five injectable inactivated influenza vaccine (IIV) options for children. Four egg-based IIVs and one cell culture-based (ccIIV), all given as intramuscular (IM) injections, are approved for children age 6 months and older:

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

One egg-based live attenuated nasal spray vaccine, FluMist (LAIV, AstraZeneca), is an option for healthy, non-pregnant people age 2 years and older: 0.2 mL (intranasal, 0.1 mL in each nostril).

Last reviewed: August 11, 2024

Children age 6 months through 8 years should receive a second influenza vaccine dose 4 weeks or more after the first dose if they meet one of the following three criteria: 1) they are receiving influenza vaccine for the first time, or 2) 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) their vaccination history is unknown. The two previous doses need not have been received during the same season or consecutive seasons.

A child who is 8 years old and is recommended to receive two doses during the current season and turns 9 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: August 11, 2024

Yes. Doses of FluMist administered in past seasons can be counted.

Last reviewed: August 11, 2024

The two doses may be the same or different products.

Last reviewed: August 11, 2024

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 a 0.5 mL dose of Afluria.

Last reviewed: August 11, 2024

Yes. Multidose vials of inactivated influenza vaccine contain a small amount of thimerosal to prevent bacterial and fungal growth in the vial. Thimerosal-containing vaccines are safe to use in children. No scientific evidence indicates that thimerosal in vaccines causes adverse events unless the patient has a severe allergy to thimerosal. Despite this, a few states have enacted legislation that restricts the use of thimerosal-containing vaccines in children. To find out if your state has such restrictions, check with your state immunization program (see www.immunize.org/official-guidance/state-policies/state-resources/ for program contact information).

Last reviewed: August 11, 2024

Yes, but only if the 9-year-old meets all of the criteria below:

  • they turned 9 years old during the current season, and
  • they had received one dose during the current season before turning 9, and
  • they have no or unknown history of receiving any previous dose of influenza vaccine before July 1 of the year of the current season.
Last reviewed: August 11, 2024

A CDC study showed a small increased risk for febrile seizures during the 24 hours after a child receives the inactivated influenza vaccine at the same time as the PCV13 vaccine or DTaP vaccine. However, the risk of febrile seizure with any combination of these vaccines is small and ACIP recommends giving these vaccines at the same visit if indicated. The risk for febrile seizures in children who received PCV15 or PCV20 concurrently with an influenza vaccine has not been studied.

See www.cdc.gov/vaccine-safety/about/febrile-seizures.html for more information about febrile seizures after vaccination.

Last reviewed: August 11, 2024

Yes. It is especially important to vaccinate during pregnancy because of the increased risk for influenza-related complications during pregnancy and the 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.

Vaccination can occur in any trimester, including the first. Only inactivated or recombinant influenza vaccines may be given during pregnancy. FluMist (LAIV), a live vaccine, should not be given during pregnancy.

Last reviewed: August 11, 2024


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Last reviewed: April 6, 2023

ACIP has recommended vaccinating during pregnancy with inactivated influenza vaccine since 1997. Studies have shown that pregnant people are at increased risk for complications, hospitalization, and even death from influenza because of the increased physiologic strain of pregnancy on their heart, lungs, and immune system. Vaccination can occur in any trimester, including the first.

Infants younger than 6 months old are at high risk of influenza-related complications, but influenza vaccine is not recommended for them because the immune response to influenza vaccination is limited before 6 months of age. Vaccinating during pregnancy provides maternal antibodies to the fetus which helps protect infants against influenza during the first 6 months of life until they can get vaccinated at age 6 months. Vaccinating pregnant people protects them, their unborn babies, and their babies after birth.

Last reviewed: August 11, 2024

Pregnant people may receive any age-appropriate inactivated or recombinant influenza vaccine. They should not be given FluMist (LAIV) because it is a live virus vaccine.

Last reviewed: August 11, 2024

Yes, unless you live in a state that has enacted legislation restricting use in pregnancy. There is no scientific evidence that thimerosal in vaccines is a cause of adverse events unless the patient has a systemic allergy to thimerosal.

Last reviewed: August 11, 2024

No. CDC’s 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.

Last reviewed: August 11, 2024

A CDC-funded study found that people who had been vaccinated early in pregnancy with an influenza vaccine containing the pandemic H1N1 (H1N1pdm09) component and who also had been vaccinated the prior season with an H1N1pdm09-containing influenza vaccine had an increased risk of spontaneous abortion (miscarriage) in the 28 days after vaccination. This study did not quantify the risk of miscarriage and did not prove that influenza vaccine was the cause of the miscarriage. Earlier studies have not found a link between influenza vaccination and miscarriage. A larger follow-up study also funded by CDC which included 3 more years of data found no association between early miscarriage and influenza vaccination regardless of previous influenza season vaccination. These results are reassuring regarding the safety of influenza vaccination during pregnancy.

CDC, ACIP, and the American College of Obstetricians and Gynecologists (ACOG) all recommend influenza vaccination during any trimester of pregnancy. Influenza poses a danger to pregnant people and the vaccine can prevent influenza in pregnant people and their infants.

Last reviewed: August 11, 2024

No. CDC and ACIP express no preference for preservative-free vaccine for infants or any other group of vaccine recipients.

No scientific evidence exists that thimerosal in vaccines is a cause of adverse events unless the patient has a systemic allergy to thimerosal. However, some states have enacted legislation that restricts the use of thimerosal-containing vaccines. Check with your state immunization program to see if your state is one of them (www.immunize.org/official-guidance/state-policies/state-resources/)

Last reviewed: August 11, 2024

People with a metabolic disease, including diabetes, should receive annual influenza vaccination with an age-appropriate inactivated or recombinant influenza vaccine.

Last reviewed: August 11, 2024

Yes. People with multiple sclerosis should be vaccinated against influenza. Multiple sclerosis is not a contraindication to any vaccine, including influenza vaccines.

Last reviewed: August 11, 2024

Although some studies have demonstrated a transient increase in replication of HIV following inactivated influenza vaccine, other studies have not found this. This temporary increase in HIV titer has not been associated with deterioration in either T-lymphocyte counts or clinical condition. Annual influenza vaccination with an age-appropriate injectable influenza vaccine benefits HIV-infected people.

Last reviewed: August 11, 2024

In November 2015, FDA licensed Fluad (aIIV, CSL Seqirus), an 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 the immune response to vaccination. 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 many other countries. In contrast to Fluzone High-Dose (HD-IIV, Sanofi), Fluad is a standard-dose vaccine, containing 15 mcg of hemagglutinin per virus per dose.

Last reviewed: August 11, 2024

Yes. Aging decreases the body’s ability to develop a good immune response after getting influenza vaccine, which places older people at greater risk of severe illness from influenza.

After years of review and deliberation, ACIP voted in June 2022 to recommend that all adults age 65 and older should preferentially receive one of the three different vaccine products that evidence suggests are likely to perform better than standard dose, unadjuvanted vaccines: Flublok recombinant influenza vaccine (RIV, Sanofi), Fluad adjuvanted vaccine (aIIV, CSL Seqirus), or Fluzone High-Dose vaccine (HD-IIV, Sanofi). However, if none of these three vaccines is available at the time of vaccination, any age-appropriate influenza vaccine may be administered.

For a thorough review of the evidence for this recommendation, see the 2022 ACIP recommendations for influenza vaccination: www.cdc.gov/mmwr/volumes/71/rr/pdfs/rr7101a1-H.pdf.

Last reviewed: August 11, 2024

Although Fluzone High-Dose (HD-IIV) and Fluad (aIIV) are FDA-licensed for people 65 years and older, in June 2024, ACIP recommended that HD-IIV or aIIV are options for administration to people age 18 through 64 years old who have had a solid organ transplant (SOT) and are on immunosuppressive medication regimens. ACIP expressed no preference for HD-IIV or aIIV over any other age-appropriate IIV or RIV vaccines for SOT recipients.

Last reviewed: August 11, 2024

No, and this is not recommended.

Last reviewed: August 11, 2024

People with cancer need to be protected from influenza. All cancer patients should receive an age-appropriate inactivated or recombinant influenza vaccine. They should not be given the live virus vaccine, FluMist (LAIV). Cancer patients and survivors are at higher risk for complications from influenza, including hospitalization and death. Here is a helpful CDC web page on cancer and influenza for patients: www.cdc.gov/cancer/flu.

Last reviewed: August 11, 2024

Inactivated influenza vaccine or recombinant influenza vaccine should be administered beginning at least 6 months after bone marrow transplant and annually thereafter for the life of the patient. A dose of vaccine can be given as early as 4 months after transplant, but a second dose should be considered in this situation. A second dose is recommended routinely for all children younger than 9 years receiving influenza vaccine for the first time.

Last reviewed: August 11, 2024

We encourage HCPs to stay home from work when they are sick. Unfortunately, by the time a HCP has symptoms of influenza, they may have already exposed many patients since the virus is shed for 1–2 days before symptoms begin. Further, many studies show that HCP often go to work while they are sick and may be infectious to others. Start planning early to make sure all employees in your work setting receive annual influenza vaccination before the influenza season begins.

Last reviewed: August 11, 2024

Because HCP provide care to patients at high risk for complications of influenza, they should be considered a high-priority group for receiving vaccination. Achieving high rates of vaccination among HCP will protect staff and their patients and reduce disease burden and healthcare costs.

In 2011, ACIP published “Immunization of Health-Care Personnel,” which includes information about all recommended vaccines (see www.cdc.gov/mmwr/pdf/rr/rr6007.pdf).

Last reviewed: August 11, 2024

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Protect vulnerable, older adult patients from influenza.
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Home of the National Adult and Influenza Immunization Summit.