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Influenza Vaccine and Disease

Quick Facts


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  • Influenza, often referred to as “flu,”“ is an infectious respiratory disease caused by type A or type B influenza viruses, which are present in the mucus membranes and secretions of the nose, throat and lungs. There are other viruses and bacteria associated with “flu-like” symptoms and it is estimated that about 80 percent of all flu-like illness that occurs every year during the “flu season” is not type A or type B influenza. Only lab confirmation can detect whether flu-like symptoms, including serious complications like pneumonia, are caused by influenza viruses or other types of viral or bacterial organisms.
  • Influenza viruses are primarily spread through coughing and sneezing but can also be transmitted by touching or using items that have been handled by an infected person and then touching one’s own mouth, or nose.
  • It is also possible for vaccine strain influenza to be transmitted by persons, who have recently received live attenuated influenza virus nasal vaccines. Vaccine strain viruses can be shed in body fluids for seven or more days after administration of live attenuated virus vaccines.
  • Symptoms of influenza include fever, chills, headache, sore throat, runny or stuffy nose, coughing, sneezing, and sometimes vomiting and diarrhea. Serious complications of influenza infection include dehydration, bronchitis, bacterial or viral pneumonia, otitis media (ear infection) and death.
  • Effective ways to stay well during the flu season and help to prevent spread of influenza or other infections all year-around include washing hands with soap and water frequently; covering mouth while coughing; staying home when sick until recovered and avoiding contact with those, who are sick until they are well; staying hydrated and eating nutritious food; lowering stress and getting plenty of exercise, sleep and vitamin D.  View NVIC's 3 minute flu prevention video to the right for healthy tips.

Influenza Vaccine

  • Two types of influenza vaccines are available in the U.S.: inactivated injectable influenza vaccine and live attenuated influenza vaccine, which is inhaled through the nose,Inactivated, injectable influenza vaccines packaged in multi-dose vials contain the mercury preservative thimerosal but inactivated influenza vaccines in single dose vials are thimerosal-free or contain trace amounts of the mercury preservative. The live attenuated nasal influenza vaccine does not contain thimerosal.
  • There are 16 different influenza vaccine products licensed in the U.S. marketed by different pharmaceutical companies.  Some of these vaccines contain only the 2009 pandemic H1N1 influenza A virus strain.  However, most seasonal influenza vaccines in the U.S. contain two type A influenza viruses and one type B influenza virus that are selected every year by the World Health Organization (WHO) and U.S. Centers for Disease Control (CDC) for inclusion in flu shots given during the current flu season.
  • The CDC’s Advisory Committee on Immunization Practices (ACIP) recommends that all Americans six months of age or older get a flu shot every year throughout life. The CDC states that babies between six and eight months old should receive two doses of influenza vaccine one month apart.
  • Reported moderate reactions to influenza vaccine include fever, local reactions (pain, redness, swelling at the site of the injection), headache, fatigue, sore throat, nasal congestion, cough, joint and muscle pain, and nausea. Reported serious complications include brain inflammation, convulsions, Bell’s palsy, limb paralysis, neuropathy, shock,  wheezing/asthma and other breathing problems. Guillain Barre Syndrome (GBS) is a disabling neurological disorder that involves temporary or permanent paralysis that can lead to death and has been causally related to influenza vaccinations.
  • As of September 1, 2015, there had been 2,071 claims filed in the federal Vaccine Injury Compensation Program (VICP) for injuries and deaths following Influenza vaccination, including 92 deaths and 1,979 serious injuries.
  • Using the MedAlerts search engine, as of September 30, 2015, there have been more than 104,465 reports of reactions, hospitalizations, injuries and deaths following influenza vaccinations made to the federal Vaccine Adverse Events Reporting System (VAERS), including 1,115 related deaths, 9,037 hospitalizations, and 2,003 related disabilities. In 2013 the Federal Advisory Commission on Childhood Vaccines (ACCV) voted to add GBS to the Vaccine Injury Table within the federal Vaccine Injury Compensation Program (VICP).

Food & Drug Administration (FDA)

Centers for Disease Control (CDC)

National Institute of Allergy & Infectious Diseases (NIAID)

Vaccine Reaction Symptoms & Ingredients

Our Ask 8, If You Vaccinate webpage contains vaccine reaction symptoms and more. Calculate vaccine ingredients for potential toxic exposures & print a vaccination plan with the Vaccine Ingredients Calculator.

Search for Vaccine Reactions

NVIC hosts MedAlerts, a powerful VAERS database search engine. MedAlerts examines symptoms, reactions, vaccines, dates, places, and more.

Reporting a Vaccine Reaction

Since 1982, the NVIC has operated a Vaccine Reaction Registry, which has served as a watchdog on VAERS. Reporting vaccine reactions to VAERS is the law. If your doctor will not report a reaction, you have the right to report a suspected vaccine reaction to VAERS.

IMPORTANT NOTE: NVIC encourages you to become fully informed about Influenza and the Influenza vaccine by reading all sections in the Table of Contents , which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

Influenza & Influenza Vaccine

The following information is provided to help you understand the disease influenza and the influenza vaccine so you can make an informed decision regarding use of this vaccine. This information is not intended to serve as medical advice but as background information that you can use to educate yourself.

Whenever making a major health care decision for yourself or your child, especially one that involves use of a pharmaceutical product such as a vaccine, obtaining information from many different sources and consulting health care professionals you trust is important. NVIC encourages you to become fully informed about influenza and Influenza vaccine and speak with one or more trusted health care professionals before making a decision about vaccination.

It is important to be equally concerned and knowledgeable about the risks of Influenza disease as we are about the risks of influenza vaccine. Both influenza and the influenza vaccine carry risks. Influenza disease has the potential to cause seizures, brain damage, and even death, just as the vaccine can.

Most of America’s medical community believes that the risk of serious injury or death from influenza is greater than the risk of injury or death which can be caused by Influenza vaccine. However, recognition of and concern about the risks of Influenza disease does not diminish our need and responsibility to acknowledge the need to minimize influenza vaccine risks. The challenge today is for parents, physicians, scientists, manufacturers and health officials to recognize the risks of both the disease and the vaccine and work to protect the health and well being of every individual.

If your doctor does not support your informed health choices, consider consulting another doctor, who will work as a partner with you and respect whatever decision you make. Below are links to specific topics regarding Influenza and Influenza vaccine for ease of use. However, the topics are interrelated and the content comprehensive.  No topic link below should be treated in a stand-alone fashion and NVIC recommends that all the information be used to reach a vaccination decision.

What is the flu?

Influenza is a respiratory infection that produces fever, chills, sore throat, muscle aches, and cough that lasts a week or more. The flu can be deadly for the elderly and those with compromised immune systems or who are suffering from diabetes, kidney dysfunction and heart disease. According to the Centers for Disease Control (CDC), each year about 36,000 Americans, mostly in these high risk groups, reportedly die from flu complications. However, there is controversy about whether the majority of the 36,000 reported deaths are caused by complications of true influenza or may be due to viral and bacterial infections which can be mistakenly attributed to influenza.

Who is at increased risk for serious complications due to the flu?

The Advisory Committee on Immunization Practices (ACIP) lists the following persons as being at increased risk for complications from influenza: anyone 65 years of age or older; nursing home residents or residents of other long-term care facilities; anyone with chronic lung or heart disorders, chronic metabolic diseases (like diabetes), kidney dysfunction, or blood disorders; anyone who is immune suppressed by medication (steroids, chemotherapy, etc) or by AIDS/HIV ; children or adolescents on long-term aspirin therapy due to possible risk of developing Reye syndrome; and women who will be in the second or third trimester of pregnancy during flu season.

What is the flu vaccine?

The flu vaccine is prepared from the fluids of chick embryos inoculated with a specific type(s) of influenza virus. The strains of flu virus in the vaccine are inactivated with formaldehyde and preserved with Thimerosal, which is a mercury derivative. (There is a limited supply of thimerosal-free influenza vaccines and it is supplied in single dose vials which do not require a preservative).

Influenza vaccines are Category B or C drugs, which means that adequate and well-controlled studies on pregnant women have not been conducted and it is not known whether these vaccines can cause fetal harm when administered to a pregnant woman or if they can affect reproduction capacity.

Below are current links for this year's influenza vaccine manufacturer's package inserts that have been licensed for use in the U.S.  As a consumer, it is important to understand and read this information carefully prior to receiving a vaccine. These links are directly from the U.S. Food & Drug Administration's website, which makes available to the public package insert information from vaccine manufacturers.  Inserts contain important information regarding drug interactions, contraindications, adverse reactions, warnings and precautions.

Quadrivalent Vaccines - Nasal
Quadrivalent Vaccines - Injected
Trivalent Vaccines - Injected
What are contraindications to the flu vaccine?

Among high risk factors listed by the CDC and the vaccine manufacturers are anyone who:  

(1) is sick with a fever;
(2) has an egg allergy; 
(3) has a mercury allergy; 
(4) has a history of Guillain-Barre syndrome. 

If immunosuppressed individuals receive the flu vaccine they may not get an adequate protective antibody response.  

Is Flu Vaccine Recommended for Children? 

One consideration with the mass use of flu vaccine in healthy children is the removal of natural antibodies to flu which are obtained from natural infection. The question of whether it is better for healthy children, who rarely suffer complications from flu, to get the flu and develop permanent immunity to that flu strain or it is better for children to get vaccinated every year to try to suppress all flu infection in early childhood is a question that has yet to be adequately answered by medical science.

Although in the past the flu vaccine has not been recommended for healthy children, today vaccination of children between the ages of 6 months and 18 years is strongly recommended by the Advisory Committee on Immunization Practices (ACIP) of the CDC and New Jersey now requires influenza vaccine for daycare and kindergarten entry.

Is the vaccine safe during pregnancy?

In years past, pregnancy was also a contraindication to flu vaccine but, today, the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control (CDC) recommends flu vaccine for women more than 14 weeks pregnant.

Influenza vaccines are Category B or C drugs, which means that adequate and well-controlled studies on pregnant women have not been conducted and it is not known whether these vaccines can cause fetal harm when administered to a pregnant woman or if they can affect reproduction capacity. 

The package inserts published by the flu vaccine manufacturers state that "Animal reproduction studies have not been conducted with influenza virus vaccine. It is also not known whether influenza virus vaccine can cause fetal harm when administered to a pregnant woman. Although animal reproductive studies have not been conducted, the prescribing health care provider should be aware of the recommendations of the Advisory Committee on Immunization Practices. The ACIP states that if used during pregnancy, administration of influenza virus vaccine after 14 weeks of gestation may be preferable to avoid coincidental association of the vaccine with early pregnancy loss."

Pregnant women should be aware that the flu vaccine contains Thimerosal, which is a mercury derivative. Mercury is toxic to the brain and has been found to be associated with brain damage and developmental delays in babies whose mothers were exposed to high levels of mercury during pregnancy.

What about mercury in the vaccine?

In 1999, the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) directed the vaccine manufacturers to take mercury out of all childhood vaccines. In October 2001, the Institute of Medicine issued a report that said it is "biologically plausible" that mercury-containing vaccines could cause injury to the brain but there have been too few scientific studies conducted to prove conclusively that mercury in vaccines has caused brain damage."

Nevertheless, the Institute of Medicine recommended that drug companies take all mercury out of all vaccines and over-the-counter drugs.

In compliance with this recommendation a preservative-free vaccine formulated for children ages 6 to 35 months, with only a trace amount of Thimerosal, is available in a limited amount. It is distinguished by a pink syringe plunger rod in the pre-filled syringe. All adult formulations still contain Thimerosal.

Many influenza vaccines in the U.S. also contain the mercury preservative, Thimerosal, in amounts above federal safety guidelines. Thimerosal free influenza vaccine is also licensed in the U.S. and it is advisable to request these vaccines in advance from your healthcare provider, if your preference is the Thimerosal free version.  Click here to determine which vaccines are Thimerosal free.

How effective is influenza vaccine? 

Like all vaccines, the flu vaccine only gives a temporary immunity to the virus strains or closely related virus strains contained in the vaccine. The only way to get natural and permanent immunity to a strain of flu is to recover naturally from the flu. Natural immunity to a particular strain of flu can be protective if that strain or closely related strains come around again in the future. However, because the vaccine only provides temporary immunity to selected strains and those strains may or may not be prevalent each year, doctors say you have to get a flu shot every year.

Every year, federal health agency officials try to guess which three flu strains are most likely to be prevalent in the U.S. the following year to determine which strains will be included in next year's flu vaccine. If they guess right, the vaccine is thought to be 70 to 90 percent effective in temporarily preventing the flu of the season in healthy persons less than 65 years old. For those over 65 years old, the efficacy rate drops to 30 to 40%  but the vaccine is assumed to be 50 to 60% effective in preventing hospitalization and pneumonia and 80% effective in preventing death from the flu. When health officials do not correctly predict which flu strains will be most prevalent and the vaccine's effectiveness is much lower for that year.

However, according to a 2011 review of existing research, inactivated influenza vaccine had a pooled efficacy of 59% for adults 18 to 65 years of age for 8 out of 12 seasons. Similar data for inactivated influenza vaccine for adults over 65 years of age and children between 2-17 years of age was lacking and require additional study. This same review found that Live-Attenuated Influenza Vaccine (LAIV), had a pooled efficacy of 83% in 9 of the 12 seasons analyzed for children aged 6 months to 7 years. Similar data for LAIV efficacy for children aged 8-17 years was lacking and requires additional study.

Throat, respiratory, gastrointestinal and ear infections caused by bacteria or other kinds of viruses are not prevented by getting an annual flu shot.

Can influenza vaccine cause injury and death?

The most common reactions, which begin within 12 hours of vaccination and can last several days are: fever, fatigue, painful joints and headache.

The most serious reaction that has been associated with flu vaccine is Guillain-Barre Syndrome (GBS) which occurs most often within two to four weeks of vaccination. GBS is an immune mediated nerve disorder characterized by muscle weakness, unsteady gait, numbness, tingling, pain and sometimes paralysis of one or more limbs or the face. Recovery takes several months and can include residual disability. Less than 5 percent of GBS cases end in death.

Brain and nerve disorders such as encephalopathy, optic neuritis, partial facial paralysis, and brachial plexus neuropathy as well as vasculitis have also been reported following the flu vaccine, although a definite causal relationship has no been established.

Adult influenza vaccine injury claims are now the leading claim submitted to the federal Vaccine Injury Compensation Program.

What About The Nasal-Spray Flu Vaccine FluMist? 

A live-virus nasal flu vaccine, FluMist, was approved for use in June 2003 and its approved use was limited to healthy people between the ages of 5 and 49. It was subsequently approved by the FDA for use in children as young as two years of age but with precautions./p>

FluMist is prepared by introducing influenza viruses into eggs where they are allowed to multiply. Fluid from the eggs is processed and sucrose, potassium phosphate and monosodium glutamate (MSG) are added as stabilizers. The antibiotic Gentamicin is also added during the manufacturing process. FluMist is a live virus vaccine and does not contain any preservatives.

Flu Mist vaccine is a Category B drug, and the product insert states:

"A developmental and reproductive toxicity study has been performed in female rats administered FluMist Quadrivalent either three times (during the period of organogenesis) or six times (prior to gestation and during the period of organogenesis), 200 microliter/rat/occasion (approximately 150 human dose equivalents), by intranasal instillation and has revealed no evidence of impaired fertility or harm to the fetus due to FluMist Quadrivalent. There are however, no adequate and well controlled studies in pregnant women. Because animal studies are not always predictive of human response FluMist Quadrivalent should be administered during pregnancy only if clearly needed."

Below is the current link for the 2015/2016 FluMist influenza vaccine manufacturer package insert.  As a consumer, it is important to understand and read this information carefully prior to receiving a vaccine. This link is directly from the U.S. Food & Drug Administration's website, which makes available to the public package insert information from vaccine manufacturers.  Inserts contain important information regarding drug interactions, contraindications, adverse reactions, warnings and precautions.    

The following information can be found within the package insert (link above):

Flu Mist Contraindications, Warnings and Precautions for:

  • pregnant women
  • nursing women
  • children under 24 months of age
  • people with asthma of any age
  • children less than five years of age with recurrent wheezing
  • people over 65 years of age
  • people with an underlying medical condition that may predispose them to complications following wild-type influenza infection
  • children receiving aspirin therapy
  • people receiving antiviral drugs
  • anyone allergic to any part of the vaccine including eggs, egg proteins, gentamicin, gelatin or arginine
  • people with a history of Guillain-Barre Syndrome (GBS)
  • people with known or suspected immune system problems or who are immune-compromised or are in close contact with immunocompromised persons

The MedImmune product insert also discusses the ability of the live virus FluMist vaccine to cause vaccine strain influenza infection and shedding: “Immune mechanisms conferring protection against influenza following receipt of FluMist Quadrivalent vaccine are not fully understood; serum antibodies, mucosal antibodies, and influenza-specific T cells may play a role. FluMist and FluMist Quadrivalent contain live attenuated influenza viruses that must infect and replicate in cells lining the nasopharynx of the recipient to induce immunity. Vaccine viruses capable of infection and replication can be cultured from nasal secretions obtained from vaccine recipients (shedding).”

Is it safe to give with other vaccines?

The safety and immunogenicity of FluMist Quadrivalent when administered concomitantly with inactivated vaccines have not been determined” and FluMist has not been studied when given simultaneously with live virus MMR and varicella zoster (chickenpox) vaccines.

How is FluMist nasal vaccine administered? 

Unlike the standard flu vaccine given by injection, which contains a dead virus, the vaccine is squirted up the nose and contains a diluted, live virus that could endanger people with weak immune systems. The live vaccine virus has been shown to shed for up to 3 weeks after receiving the vaccine. 

What are the reactions and side effects of FluMist?

In adults the most common side effects were runny nose, cough, sore throat, headache, muscle aches, fever, chills and tiredness or weakness. 

Reported adverse effects to FluMist in children include runny nose, nasal congestion, cough, sore throat, headache, irritability, decreased activity, fever, chills, muscle aches, and vomiting.  Other adverse events that occurred in children were abdominal pain, asthma, bronchitis, conjunctivitis, viral syndrome, otitis media (middle ear infection), and wheezing or shortness of breath.

Questions to Ask Doctors about Influenza Vaccine

NVIC’s If You Vaccinate, Ask 8! Webpage downloadable brochure suggests asking eight questions before you make a vaccination decision for yourself, or for your child. If you review these questions before your appointment, you will be better prepared to ask your doctor questions.  Also make sure that the nurse or doctor gives you the relevant Vaccine Information Statement (VIS) for the vaccine or vaccines you are considering well ahead of time to allow you to review it before you or your child gets vaccinated. Copies of VIS for each vaccine are also available on the CDC's website and there is a link to the VIS for influenza vaccine on NVIC's “Quick Facts” at the top of this page.

It is also a good idea to read the vaccine manufacturer product insert that can be obtained from your doctor or public health clinic because federal law requires drug companies marketing vaccines to include certain kinds of vaccine benefit, risk and use information in product information inserts that may not be available in other published information. 

Other questions that may be useful to discuss with your doctor before getting the influenza vaccine are: 

  • If other vaccines in addition to influenza vaccine are scheduled for my child at this office visit, am I allowed to modify the schedule so fewer vaccines are given at once?
  • What should I do if my child has a high fever or appears very ill after vaccination?
  • What other kinds of reaction symptoms should I call to report after influenza vaccination?
  • If the influenza vaccine doesn’t protect my child, do I have any other options for preventing measles infection?

Under the National Childhood Vaccine Injury Act of 1986, doctors and all vaccine providers are legally required to give you vaccine benefit and risk information before vaccination; record serious health problems following vaccination in the permanent medical record; keep a permanent record of all vaccines given, including the  manufacturer’s name and lot number; and report serious health problems, injuries and deaths that follow vaccination to VAERS.

Remember, if you choose to vaccinate, always keep a written record of exactly which shots/vaccines you or your child have received, including the manufacturer’s name and vaccine lot number. Write down and describe in detail any serious health problems that develop after vaccination, and keep vaccination records in a file you can access easily.

It also is important to be able to recognize a vaccine reaction and seek immediate medical attention if the reaction appears serious, as well as know how to make a vaccine reaction report to federal health officials at the Vaccine Adverse Reporting System (VAERS). NVIC’s Report  Vaccine Reactions—It’s the Law webpage can help you file a vaccine reaction report yourself to VAERS if your doctor fails or refuses to make a report.

NVIC Press Releases, Statements and Commentaries

Statements and Commentaries

Press Releases

Additional Bibliography of References

Medical Literature

Media Articles

This portion of our website in also in the process of being updated as new information on influenza vaccines in use this season is made known.  Please continue to check back for the latest information.

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