- Side Effects
- Drug Interactions
- Pregnancy & Breastfeeding
- What Else to Know
Drug Class: Vaccines, Inactivated, Viral
What is the influenza virus vaccine, and what is it used for?
The influenza virus vaccine is a sterile biologic product that provides immunity against seasonal influenza. Influenza virus vaccine works by stimulating the body’s immune system to produce antibodies against influenza virus, and protects a person from developing infection when exposed to the virus. The current influenza vaccine is a quadrivalent vaccine that protects against infection from four strains of influenza virus.
- Influenza virus vaccines are inactivated viral vaccines that contain particles of proteins or genetic material from influenza virus. Most influenza virus vaccines are prepared from viruses grown in embryonated chicken eggs, however, there are also egg-free vaccines produced in insect or mammalian cells. The viruses are then inactivated and purified to eliminate their disease-causing capability. Inactivated viral vaccines may also contain substances that preserve and stabilize the vaccine, and enhance immune response.
- The primary active components of influenza virus vaccines are the surface proteins (antigens) known as hemagglutinins that help the virus adhere to a human cell, enter inside and replicate, and DNA/RNA fragments from the virus. The immune system of the vaccinated individual produces antibodies to the influenza virus and if exposed to it later, the immune system recognizes the viral antigen and fights infection by preventing the virus from attaching and entering the host cell.
- There are several types of influenza vaccines approved by the FDA, some of which are standard flu vaccines for all individuals older than 6 months, some are meant only for adults, and some are intended for individuals older than 65 years of age. A person’s suitability for vaccination and the type of flu vaccine may be determined by various factors including their age, health, and allergies to any of the vaccine components.
- Flu vaccines are mostly administered as intramuscular (IM) injections, but an additional option available is an egg-based, live, attenuated flu nasal spray vaccine with the brand name FluMist Quadrivalent, made with weakened live influenza viruses, approved for use in individuals of age 2 years to 49 years. This vaccine is not recommended for use in pregnant people, immunocompromised people, or people with certain medical conditions.
- Do not administer the influenza virus vaccine to anyone with a history of severe allergic reactions (anaphylaxis) to any component of the vaccine, including egg protein, or to anyone who has had a severe reaction to previous flu vaccination.
- Medical facilities for appropriate management of anaphylactic reactions following the vaccination should be available at the vaccination facility.
- Influenza virus vaccine may be associated with an elevated risk for Guillain-Barre syndrome (GBS), although the evidence is inconclusive. If a person has experienced GBS within 6 weeks after a previous flu vaccine, weigh potential benefits and risks before administering the flu vaccine.
- Vaccine administration to individuals with minor illnesses without fever may be acceptable, but defer the vaccine in febrile illnesses until the illness is resolved.
- Immune response to the vaccine may be lower in individuals who are immunocompromised, including those on immunosuppressant or corticosteroid treatments.
- The influenza virus vaccine may not protect all vaccine recipients against disease.
- Fainting has been reported in some individuals, following vaccination. Follow precautions to prevent falling and injury.
- The tip of the syringe may contain natural rubber latex, to which some individuals may be sensitive. Exercise caution.
- Intramuscular injections may cause hematoma in people with bleeding disorders, use them with caution.
- Do not mix any other vaccine with the influenza virus vaccine. If other vaccines must be administered concurrently, administer them separately at different sites.
What are the side effects of the flu vaccine?
Common side effects of influenza virus vaccine include:
- Local reactions at the injection site including:
Flu shot side effects in adults
- Systemic reactions common in adults:
Flu shot side effects in children and adolescents
- Systemic reactions common in infants, children, and adolescents:
Less common symptoms of influenza virus vaccine include:
- Local reactions at the injection site including:
- Abdominal pain and distress
- Swallowing difficulty (dysphagia)
- Swollen tongue
- Swelling of the injected limb, lasting longer than a week
- Facial swelling (edema)
- Feeling faint (presyncope)
- Fainting (syncope)
- Blood vessel dilation (vasodilation)
- Blood vessel inflammation (vasculitis)
- Henoch-Schonlein purpura, a condition that makes small blood vessels in skin, joints, kidneys and gastrointestinal tract get inflamed and bleed
- Chest pain
- Rapid heart rate (tachycardia)
- Hot flash
- Nasal inflammation (rhinitis)
- Throat inflammation (pharyngitis)
- Throat swelling (pharyngeal edema)
- Shortness of breath (dyspnea)
- Limb pain
- Musculoskeletal pain
- Body pain
- Weakness (asthenia)
- Abnormally low motor activity (hypokinesia)
- Muscle weakness (myasthenia)
- Bell’s palsy
- Cranial nerve palsy
- Impaired mobility of the injected arm
- Inflammation of the spinal cord (myelitis)
- Inflammation of a section of the spinal cord (transverse myelitis)
- Inflammation of the brain and spinal cord (encephalomyelitis)
- Brain disease (encephalopathy)
- Feeling hot
- Febrile seizure
- Nerve pain (neuralgia)
- Nerve inflammation (neuritis)
- Nerve disease (neuropathy)
- Guillain-Barre syndrome, a condition in which the immune system attacks the nerves
- Reduced skin sensation (hypoesthesia)
- Tingling and numbness (paresthesia)
- Voice disorder
- Eye pain
- Swelling of eye
- Light sensitivity
- Eyelid edema
- Red eye (ocular hyperemia)
- Optic neuritis
- Optic neuropathy
- Hypersensitivity reactions, including:
- Skin reactions that include:
- Excessive sweating (diaphoresis)
- Low platelet count (thrombocytopenia)
- Swelling of lymph nodes (lymphadenopathy)
Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:
- Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
- Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
- Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
- Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.
This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.
What are the dosages of the flu vaccine?
Intramuscular (IM) suspension
- 0.25 mL/prefilled syringe (Fluzone Quadrivalent)
- 0.5 mL/prefilled syringe (Afluria Quadrivalent, Fluzone Quadrivalent, FluLaval Quadrivalent, Fluarix Quadrivalent)
- 0.5 mL/vial (Fluzone Quadrivalent)
- 5 mL/vial (Afluria Quadrivalent, Fluzone Quadrivalent, FluLaval Quadrivalent)
IM suspension injection, high-dose
- 240 mcg/0.7mL (Fluzone High-dose Quadrivalent)
- 0.5 mL/prefilled syringe (Flublok Quadrivalent)
Emulsion for IM injection
- 0.5 mL/prefilled syringe (Fluad Quadrivalent)
- CDC’s ACIP recommends that everyone aged 6 months and older receive an annual influenza vaccination
- For more vaccine information see http://www.cdc.gov/vaccines/
Fluarix Quadrivalent, Fluzone Quadrivalent, FluLaval Quadrivalent, Afluria Quadrivalent, Fluzone High-Dose Quadrivalent, Flublok Quadrivalent
- 0.5 mL IM x1 dose/season
- Not indicated for adults below 65 years
- The Advisory Committee on Immunization Practices (ACIP) recommends Flublok Quadrivalent for vaccination of persons with egg allergy of any severity
- Flublok Quadrivalent does not use the influenza virus or chicken eggs in its manufacturing process
Indicated for use in patients 65 years or above
Afluria Quadrivalent, Fluzone Quadrivalent, FluLaval Quadrivalent, Fluad Quadrivalent,
- 0.5 mL IM x 1 dose/season
Fluzone High-Dose Quadrivalent
- 0.7 mL IM x 1 dose/season
- Safety and efficacy not established for pediatric use (below 18 years)
Fluarix Quadrivalent, Afluria Quadrivalent, FluLaval Quadrivalent, or Fluzone Quadrivalent
Children below 6 months
- Safety and efficacy not established
Children 6 months up to 9 years
- Fluarix Quadrivalent
- Not previously vaccinated: 0.5 mL IM x 2 doses
- Previously vaccinated in a previous season: 0.5 mL IM x 1-2 doses
- Afluria Quadrivalent, FluLaval Quadrivalent, or Fluzone Quadrivalent
- Children 6 to 36 months and not previously vaccinated: 0.25 mL or 0.5 IM x 2 doses
- Children 6 to 36 months and previously vaccinated in a previous season: 0.5 mL IM x 1-2 doses
- Children 36 months to 9 years and not previously vaccinated: 0.5 mL IM x 2 doses
- Children 36 months to 9 years and previously vaccinated in a previous season: 0.5 mL IM x 1-2 doses
- Flucelvax Quadrivalent
- Children 4 to 9 years: 0.5 mL 1-2 doses
Children 9 years or above
- For all formulations
- 0.5 mL IM x 1 dose
Contains the following 4 viral strains for the 2022-2023 Northern Hemisphere season
- A/Victoria/2570/2019 (H1N1)pdm09-like virus (no change from last season)
- A/Darwin/9/2021 (H3N2)-like virus (new for 2022-2023)
- B/Austria/1359417/2021 (B/Victoria lineage)-like virus (new for 2022-2023)
- B/Phuket/3073/2013-like virus (B/Yamagata lineage) (no change from last season)
What drugs interact with the flu vaccine?
Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.
- Severe interactions of the influenza virus vaccine include:
- The influenza virus vaccine has serious interaction with at least 96 different drugs.
- The influenza virus vaccine has serious interaction with at least 50 different drugs.
- Mild interactions of influenza virus vaccine include:
The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.
It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.
Subscribe to MedicineNet's General Health Newsletter
Pregnancy and breastfeeding
- There is insufficient information on influenza virus vaccine use in pregnant women to determine vaccine-related fetal malformations or adverse effects. Animal studies showed no evidence of fetal harm with flu vaccination during pregnancy.
- Pregnant women are at a higher risk than non-pregnant women for influenza-related complications. Pregnant women who contract influenza may be at an increased risk for preterm labor and delivery.
- FluMist Quadrivalent live attenuated nasal spray vaccine should not be used in pregnant women.
- Fluad Quadrivalent is approved only for people older than 65 years of age.
- There are no data on the presence of the influenza virus vaccine in breastmilk, or its effect on milk production or on the breastfed infant. The decision to breastfeed should be made after considering the developmental and health benefits of breastfeeding, along with the potential adverse effects on the infant from the vaccine or the mother’s susceptibility to contracting flu infection.
- There is a pregnancy exposure registry that monitors pregnancy outcomes in women following influenza virus vaccination during pregnancy. Healthcare providers are encouraged to enroll women by contacting:
- FluLaval Quadrivalent, Fluarix Quadrivalent: 1-888-452-9622
- Afluria Quadrivalent: 1-855-358-8966 or send an email to Seqirus at [email protected]
- Fluzone Intradermal Quadrivalent or Fluzone Quadrivalent: Sanofi Pasteur Inc at 1-800-822-2463
- Flublok Quadrivalent: Protein Sciences Corporation 1-888-855-7871
What else should I know about influenza virus vaccine?
- All flu vaccines for the 2022-2023 season are quadrivalent vaccines, designed to protect against four different flu viruses, including two influenza A viruses and two influenza B viruses.
- Centers for Disease Control and Prevention (CDC) recommends all people 6 months and older to get a flu vaccine every year, and there are many flu vaccine options to choose from.
- For more information, visit https://www.cdc.gov/flu/prevent/flushot.htm
The influenza virus vaccine is a sterile biologic product that provides immunity against seasonal influenza. The current influenza vaccine is a quadrivalent vaccine that protects against infection from four strains of influenza virus. Common side effects of influenza virus vaccine include local reactions at the injection site, headache, fatigue, feeling ill (malaise), muscle pain (myalgia), joint pain (arthralgia), diarrhea, nausea, vomiting, loss of appetite (anorexia), chills, shivering, fever, mouth and throat (oropharyngeal) pain, and others. Pregnant women are at a higher risk than non-pregnant women for influenza-related complications as well as increased risk for preterm labor and delivery.
Multimedia: Slideshows, Images & Quizzes
Cold, Flu, and Cough: 13 Foods to Eat When Fighting the Flu
The best foods to eat when you have the flu soothe symptoms and help you feel better faster. Good foods to eat with the flu...
Cold, Fever and Flu Symptoms in Children: Medications and Home Remedies
How long does a cold last? How long is a cold contagious? Colds and fevers are some of the most common ailments in children....
Cold and Flu: Finding Fast Cough Relief
Remedies for coughing to relieve symptoms, thin mucus, and clear phlegm include cough syrup and honey in hot water. Use...
Stomach Flu: Types, Symptoms, and Treatment
Stomach flu symptoms need treatment if vomiting, diarrhea, and dehydration are severe. Stomach flu is contagious and some cases...
How to Get Rid of a Cold: Natural Remedies
What home remedies work to get rid of a cold fast? Many claim cold symptoms and flu symptoms can be relieved with Echinacea,...
Cold & Flu Quiz: Influenza vs. Common Cold
Aches? Pain? Fever? This Cold & Flu Quiz tests your knowledge on the difference between coming down with the common cold and...
Picture of Influenza Virus
The flu is caused by viruses that infect the respiratory tract which are divided into three types, designated A, B, and C. See a...
Home Remedies for Sick Children
Home remedies for sick babies, toddlers, and kids can help with things like colds, flu, cough, sore throat, stuffy nose, fever,...
Cold, Flu, & Cough: How to Clean After Illness
This slideshow gives you a room-by-room look at how and what to disinfect after someone in your family has been sick.
A Cold or The Flu? How to Tell the Difference
Discover the difference between cold vs. flu symptoms. Learn the difference between cold and flu symptoms. Read about cold and...
Cold, Flu, and Cough: How to Avoid Infectious Diseases
The right habits will lower your chances of catching an infectious disease. Learn what you can do to help yourself stay healthy.
Germs: Everyday Items with the Most Bacteria
Explore the germiest places you may encounter daily. Bacteria is everywhere. Learn tips to avoid germs and bacteria in public...
Cold and Flu: The Truth About Hand Sanitizer
Hand sanitizers are a convenient way to kill germs. But do they really work? Here's what we found.
Flu Shots: 10 Facts About Flu Shots
What are the side effects of a flu shot? Who should get vaccinated? Learn the benefits and risks of vaccination for seasonal...
Cold, Flu, & Cough: Symptoms of Immune System Problems
Your immune system is your main line of defense against infection and illness. Learn the warning signs that yours isn’t working...
Related Disease Conditions
Can You Take Tylenol Cold and Flu While Breastfeeding?
Tylenol is a well-known brand of acetaminophen and it is safe and effective for fever and pain.A void combined products like Tylenol Cold and Flu while you are breastfeeding.
Diabetes and Safe Medications for Colds & Flu
If you have diabetes and catch a cold or the flu, can be more difficult to recover from infections and their complications, for example, pneumonia. Home remedies and over-the-counter (OTC) drugs used for the treatment of the signs and symptoms of colds and the flu may affect blood sugar levels in people with diabetes.Some medications are OK to take if you have diabetes get a cold or the flu include nonsteroidal anti-inflammatory drugs or NSAIDs, like acetaminophen (Tylenol) and ibuprofen (Motrin) to control symptoms of fever and pain. Most cough syrups are safe to take; however, check with your pediatrician to see what medications are safe to give your child if he or she has type 1 or 2 diabetes. If you have diabetes and are sick with a cold or flu, you need to check your blood sugar levels more frequently. Continue taking your regular medications. Eat a diabetic low-glycemic index diet rich in antioxidants. To prevent colds and the flu drink at least eight 8 ounce glasses of water a day. To replenish fluids, drink sports drinks like Gatorade and Pedialyte to replenish electrolytes. Avoid people who are sick, sneezing, coughing, or have other symptoms of a cold or flu.
Influenza (flu) is a respiratory illness caused by a virus. Flu symptoms include fever, cough, sore throat, runny nose, headache, fatigue, and muscle aches. The flu may be prevented with an annual influenza vaccination.
How Long Is a Cold or Flu Contagious?
Viruses cause the common cold and the flu. Early symptoms and signs for a cold and the flu are similar, however, flu symptoms are typically more severe than cold symptoms. Cold and flu viruses are transmitted typically via coughing or sneezing.
Is Parainfluenza the Same as the Flu?
Despite their similar names, parainfluenza and influenza (flu) are not the same infections. They both can cause respiratory infections, which can trigger identical symptoms and spread in the same way. Parainfluenza is caused by the Paramyxoviridae virus, whereas influenza is caused by the Orthomyxoviridae virus family.
Bird Flu (Avian Influenza, Avian Flu)
Bird flu (avian flu, avian influenza) infection in humans may result from contact with infected poultry. There is a vaccine to prevent human infection with the H5N1 strain of the avian flu virus.
COVID-19 vs. Flu vs. Cold
When you're feeling sick, it can be difficult to distinguish the symptoms of a COVID-19 infection from the symptoms of the common cold or the flu (influenza). While fever is common with the flu and COVID-19, sneezing is typically only associated with colds. Though sore throats are typical with colds, they are uncommon with COVID-19 infections and the flu.
Swine Flu (Swine Influenza A [H1N1 and H3N2])
Novel H1N1 influenza A virus infection (swine flu) is an infection that generally is transferred from an infected pig to a human, however there have been reported cases where infection has occured with no contact with infected pigs. Symptoms of swine flu are "flu-like" and include fever, cough, and sore throat. Treatment is generally with the antibiotics oseltamivir (Tamiflu) or zanamivir (Relenza).
Which Flu Is Worse A or B?
Flu or influenza is a contagious (spreads from person to person) viral illness that affects the respiratory tract (the nose, throat and lungs). Type A influenza is generally considered worse than type B influenza.
How Long Does Type B Flu Usually Last?
Type B flu symptoms typically last about 5-7 days, although they may go away sooner if you have been vaccinated. Learn about flu symptoms, spread, treatment, and when to seek medical help. Check out the center below for more medical references on the flu, including multimedia (slideshows, images, and quizzes), related diseases, treatment, diagnosis, medications, and prevention or wellness.
How Long Does the Flu Last in Seniors?
What is the flu? Learn the signs of the flu in seniors and when you need to call a doctor.
How Do You Cure the Flu Quickly?
Flu or influenza is a common viral disease affecting the respiratory system. This infectious disease is caused by the influenza virus. Most cases of flu are self-limiting and can be easily managed at home.
Can You Have the Flu Without a Fever?
Since not every individual experiences all of the flu symptoms, it is possible to have the flu without having a fever.
How Long Do Flu Symptoms Last in Toddlers?
What is the flu, and how long do symptoms last in kids? Learn the signs of the flu and find out what medicines may help.
What Are The Side Effects of the H1N1 Flu Vaccine?
H1N1, also known as the swine flu, most recently caused an outbreak in 2009. The vaccine for it used to be a separate shot, but is now included in your yearly flu shot. The side effects are similar to the flu shot, and are usually minor.
Omicron Variant Vs. Flu Symptoms: Similarities and Differences
Here are the similarities and differences of the Omicron COVID-19 variant and flu symptoms.
How Does the Flu Affect the Immunocompromised?
Influenza, or the flu, is a respiratory illness caused by the influenza virus. It is generally a mild illness that can be treated at home with over-the-counter medications and rest. However, for people with compromised immune systems, the flu can be much more serious. This includes the increased risk of complications, prolonged illness, weakened immune system, and increased risk of death.
Can Flu Cause Serious Health Problems?
Influenza can cause serious health problems such as pneumonia, bronchitis, and myositis. Check out the center below for more medical references on the flu, including multimedia (slideshows, images, and quizzes), related disease conditions, treatment and diagnosis, medications, and prevention or wellness.
Can the Flu Shot Harm My Unborn Baby?
Getting the flu shot will not harm your unborn baby at any stage of pregnancy. The flu shot is both safe and recommended to protect you and your baby from the virus. Don’t however, get the nasal spray vaccine, which is not recommended for pregnant women.
Treatment & Diagnosis
- Cold & Flu FAQs
- Nasal Flu Vaccine for Children
- Flu: Waiting for Flu Shots, a Real Reality Show
- Flu Shot Fiasco, Critical Incident Report
- Swine Flu Symptoms, Diagnosis, and Vaccination
- What to Do if You Think You Have H1N1 Swine Flu Virus
- H1N1 Swine Flu Can Infect Some Pets
- Tamiflu for Bird Flu?
- Flu Shot Side Effects
- Will a Flu Shot Prevent Pleurisy?
- Flu Shots - Next Big Influenza Outbreak
- Bird Flu: What Is Bird Flu? Should We Be Concerned?
- Influenza A (H3N2)v: What Goes Around Comes Around
- Flu Free: How to Fend Off the Flu
Medications & Supplements
- Haemophilus influenzae type B vaccine
- influenza virus vaccine - intramuscular, Afluria, Fluarix, Flublok, Flu
- Side Effects of Tamiflu (oseltamivir)
- FluMist, FluMist Quadrivalent influenza vaccine live intranasal
- Side Effects of FluMist (influenza nasal vaccine live)
- Fluzone High-Dose (Influenza Vaccine)
- Afluria Quadrivalent (Influenza Vaccine)
- influenza virus vaccine - syringe intradermal, Fluzone
Prevention & Wellness
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.