CDC and FDA monitor the safety of all vaccines licensed in the United States, including seasonal influenza vaccines. Studies support the safety of annual influenza vaccination in children and adults.
This summary provides information on four types of influenza vaccines:
- Egg-based inactivated influenza vaccine (egg-based IIV4s)
- Cell culture-based inactivated influenza vaccine (ccIIV4)
- Recombinant influenza vaccine (RIV4)
- Live attenuated influenza vaccine (LAIV4)
Three topic areas are reviewed for each vaccine type:
- Adverse Events: Symptoms or health problems that occur following or during administration of a vaccine that might be caused by the vaccine or might be coincidental and not related to vaccination.
- Contraindications: A condition in a vaccine recipient that increases the risk for a serious adverse reaction. A vaccine should not be administered when a contraindication is present.
- Precautions: A condition in a vaccine recipient that might increase the risk for a serious adverse reaction, might cause diagnostic confusion, or might compromise the ability of the vaccine to produce immunity. In general, administration of a vaccine should be deferred when a precaution to that vaccine is present. However, a health care provider may determine that vaccination is indicated in the presence of a precaution because the benefit of protection from the vaccine outweighs the risk for an adverse reaction.
Additionally, general vaccine safety information on the following topics appears at the end of this summary:
- Vaccination of persons with egg allergies
- National Vaccine Injury Compensation Program (VICP)
- Reporting adverse events to the Vaccine Adverse Event Reporting System (VAERS)
- Additional resources for clinicians
Egg-Based Inactivated Influenza Vaccines (Egg-Based IIV4s)
Egg-based IIV4s are administered by injection. These vaccines are made with influenza viruses that have been grown in eggs and contain very small residual amounts of egg proteins. The viruses are inactivated, and cannot cause influenza.
Some people experience no adverse events after receiving egg-based IIV4s. Some adverse events are relatively common (such as mild tenderness or pain at the injection site), some are rare (such as Guillain-Barre syndrome).
- Pain and other injection site reactions are frequently reported after administration of inactivated influenza vaccines in both children and adults. They include symptoms such as pain, redness, and swelling at the injection site. These side effects may affect your ability to do daily activities, but they should go away in a few days.
- Fever, malaise, myalgia, and other systemic symptoms can also occur after vaccination. These reactions are more common among individuals who have had no previous exposure to the influenza virus antigens in the vaccine (e.g., young children). These symptoms are generally less common in adults.
- Vaccines can be associated with allergic (immediate hypersensitivity) reactions that range in severity from mild reactions to anaphylaxis.
- In some seasons, IIV has been associated with febrile seizures in young children, particularly when given together with 13-valent pneumococcal conjugate vaccine (PCV13) and diphtheria, tetanus and pertussis (DTaP) vaccines.
- Guillain–Barré Syndrome (GBS), a serious neurological condition that can cause paralysis occurs rarely following influenza vaccination. The cause of GBS is unknown. GBS is also associated with some gastrointestinal and upper respiratory infections.
- IIV, like other injections, can also be associated with syncope (fainting).
IIV should not be administered to infants younger than 6 months of age, because they are not approved for this age group.
Egg-based IIV4s are contraindicated for the following groups:
- People who have experienced a severe or life threatening allergic reaction (e.g., anaphylaxis) to a prior dose of any influenza vaccine (any egg-based IIV, ccIIV, RIV, or LAIV of any valency).
- People who have had a severe allergic reaction to any component of a specific influenza vaccine (other than egg protein) should not receive that vaccine or other vaccines containing that component. Health care providers should consult the package inserts for vaccine components.
Although a history of severe allergic reaction (e.g., anaphylaxis) to egg is a labeled contraindication to the use of egg-based IIV4s and LAIV4, ACIP recommends that persons with a history of egg allergy may receive any licensed, recommended influenza vaccine that is otherwise appropriate for their age and health status. See, Vaccination of Persons with Egg Allergies, below.
- GBS within 6 weeks of a previous dose of any influenza vaccine.
- Presence of a moderate or severe acute illness with or without a fever. Individuals who were hospitalized with an acute illness but now are well enough to be discharged can be vaccinated
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Cell Culture-based Inactivated Influenza Vaccine (ccIIV4)
Flucelvax Quadrivalent (cell culture-based quadrivalent inactivated influenza vaccine, ccIIV4) is approved for use in individuals 6 months of age and older. This vaccine contains influenza vaccines that have been grown in a cell culture instead of in eggs. These viruses have been inactivated and cannot cause influenza.
The safety profile of ccIIV4 is similar to that of other (egg-based) IIV4s. (See, Adverse Events Following Egg-Based IIV4s, above).
ccIIV4 should not be administered to infants younger than 6 months of age, because it is not approved for this age group.
In addition, ccIIV4 is contraindicated for individuals who have had a severe allergic reaction (e.g., anaphylaxis) to any ccIIV of any valency, or to any component of ccIIV4.
Precautions to the use of egg-based IIV4s include:
- GBS within 6 weeks of a previous dose of any influenza vaccine.
- Presence of a moderate or severe acute illness with or without a fever. Individuals who were hospitalized with an acute illness but now are well enough to be discharged can be vaccinated
- History of severe allergic reaction to a previous dose of any other influenza vaccine (i.e., any egg-based IIV, RIV, or LAIV of any valency). If administered in these instances, vaccination should occur in a medical setting under supervision of a provider who can recognize and manage a severe allergic reaction. Providers can also consider consultation with an allergist to help identify the vaccine component responsible for the previous severe allergic reaction.
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Recombinant Influenza Vaccine (RIV4)
RIV4 is administered as an injection. This vaccine is produced in an insect cell line using genetic sequences from cell-derived influenza viruses and is manufactured without the use of influenza viruses or eggs. This vaccine does not contain influenza viruses and cannot cause influenza.
Read more about how recombinant flu vaccines are made.
Like other injectable influenza vaccines, RIV4 may cause pain, redness, and swelling at the injection site as well as fever, malaise, and myalgias. In some studies, some local injection site reactions were less common with RIV than with IIVs.
RIV4 should not be administered to persons younger than 18 years of age, because it is not approved for this age group.
In addition, ccIIV4 is contraindicated for individuals who have had a severe allergic reaction (e.g., anaphylaxis) to any RIV of any valency, or to any component of RIV4.
- History of GBS within 6 weeks of previous dose of any influenza vaccine.
- Presence of a moderate or severe acute illness with or without a fever. Individuals who were hospitalized with an acute illness but now are well enough to be discharged can be vaccinated
- History of severe allergic reaction to a previous dose of any other influenza vaccine (i.e., any egg-based IIV, ccIIV, or LAIV of any valency). If administered in these instances, vaccination should occur in a medical setting under supervision of a provider who can recognize and manage a severe allergic reaction. Providers can also consider consultation with an allergist to help identify the vaccine component responsible for the previous severe allergic reaction.
Live Attenuated Influenza Vaccine (LAIV4)
LAIV4 is administered intranasally. Rhinitis (runny nose) and nasal congestion occur more commonly after LAIV than IIV or placebo in adults and children.
- The most common adverse reactions to LAIV are runny nose or nasal congestion in all ages, fever >100°F in children 2-6 years of age, and sore throat in adults.
- One study of 8,352 children aged 6 through 59 months showed that younger children aged 6 through 23 months (an age group for which LAIV is not licensed) had increased rates of wheezing in the 42 days after LAIV (6%) than after IIV (4%). Children aged 24 through 59 months had similar rates of wheezing after LAIV (2%) and IIV (3%).
- According to the LAIV package insert:
- In children aged 2 through 6 years, fever >100° F occurred more often after first dose LAIV (16%) than placebo (11%). Adults receiving LAIV did not have an increased risk for fever after vaccination compared with placebo.
- In adults the following other adverse events were reported more often after LAIV than after an intranasal placebo: headache, sore throat, tiredness/weakness, muscles aches, cough, chills, and sinusitis.
LAIV should not be administered to children aged <2 years of age or to adults aged ≥50 years of age, because it is approved only for persons aged 2 through 49 years.
In addition, conditions and situations in which LAIV4 is either contraindicated or in which ACIP recommends that it should not be used include:
- Individuals with a history of severe allergic reaction (e.g., anaphylaxis) to a previous dose of any influenza vaccine (any egg-based IIV, ccIIV, RIV, or LAIV of any valency), or to any component of LAIV4 (other than egg protein).
- Children or adolescents receiving aspirin or other salicylates (because of the association of Reye syndrome with wild-type influenza virus infection).
- Children aged 2 through 4 years who have received 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
- Children and adults who are immunocompromised due to any cause, including but not limited to immunosuppression caused by medications, congenital or acquired immunodeficiency states, HIV infection, anatomic asplenia, or functional asplenia (e.g., due to sickle cell anemia).
- Close contacts and caregivers of severely immunosuppressed persons who require a protected environment (alternatively, they should avoid contact with such persons for 7 days after receipt of LAIV.)
- Pregnancy
- Persons with active communication between the CSF and the oropharynx, nasopharynx, nose, or ear or any other cranial CSF leak.
- Persons with cochlear implants.
- Individuals who have recently taken influenza antiviral medications. LAIV4 contains live influenza viruses, and it is possible that influenza antiviral medications might interfere with replication of these viruses. This has not been studied, and the time frame for possible interference is not known. Based on the half-lives of the medications, interference might be possible if influenza antivirals are taken:
- From 48 hours before to two weeks after LAIV4 administration for oseltamivir and zanamivir.
- From 5 days before to two weeks after LAIV4 administration for peramivir.
- From 17 days before to two weeks after LAIV4 administration for baloxavir.
- These time intervals might be longer in the setting of medical conditions which delay clearance of medications.
Although a history of severe allergic reaction (e.g., anaphylaxis) to egg is a labeled contraindication to the use of egg-based IIV4s and LAIV4, ACIP recommends that persons with a history of egg allergy may receive any licensed, recommended influenza vaccine that is otherwise appropriate for their age and health status.
- GBS within 6 weeks of a previous dose of any influenza vaccine
- Presence of a moderate or severe acute illness with or without a fever.5Individuals who were hospitalized with an acute illness but are now well enough to be discharged can be vaccinated.
- Asthma in children aged 5 years and older.
- Individuals who have other medical conditions that migh place them at increased risk for complications from influenza, including:
- Other chronic disorders of the pulmonary or cardiovascular system (except hypertension)
- Neurological or neuromuscular diseases
- Metabolic disease, such as diabetes mellitus
- Renal or hepatic dysfunction
- Hematologic disorders, such as hemoglobinopathies
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Vaccination of Persons with Egg Allergies
People with egg allergies can receive any licensed, recommended age-appropriate influenza (flu) vaccine (IIV4, RIV4, ccIIV4, or LAIV4) that is otherwise appropriate. People who have a history of severe egg allergy (those who have had any symptom other than hives after exposure to egg) should be vaccinated in a medical setting, supervised by a health care provider who is able to recognize and manage severe allergic reactions. Two completely egg-free flu vaccine options are available: Flublok Quadrivalent recombinant flu vaccine and Flucelvax Quadrivalent cell-based flu shot.
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Reporting Adverse Events
The National Childhood Vaccine Injury Act of 1986 requires health care providers to report any adverse event listed by the vaccine manufacturer as a contraindication to future doses of the vaccine or any adverse event listed in the VAERS Table of Reportable Events Following Vaccination (https://vaers.hhs.gov/docs/VAERS_Table_of_Reportable_Events_Following_Vaccination.pdf) that occurs within the specified period after vaccination. In addition, health care providers are encouraged to report all clinically significant adverse events after influenza vaccines and other vaccines to VAERS, even if it is uncertain that the vaccine caused the event. Anyone may submit a report to VAERS.
Anonymous VAERS data is publicly available through the CDC Wide-ranging Online Data for Epidemiologic Research (WONDER).
Additional information about VAERS and how to file a report is available on the VAERS website.
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The National Vaccine Injury Compensation Program
The National Vaccine Injury Compensation Program (VICP) is a federal program that was created to compensate people who might have been injured by certain vaccines.
Individuals who believe they might have been injured by a vaccine can learn about the program and about filing a claim by calling 1-800-338-2382 or visiting the VICP website.