The Facts on the Flu
From the National Vaccine Information Center
Become educated about the flu (and its benefits and risks) and the flu vaccine (and its benefits and risks). Make an informed decision after consulting multiple sources of information and discussing your questions with one or more health professionals.
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. Each year, about 36,000 Americans, mostly in these high-risk groups, reportedly die from flu complications such as pneumonia.
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
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.
Every year, federal health agency officials try to guess which three flu strains are most likely to be prevalent in the United States 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 70-90% 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 30-40%, but the vaccine is thought to be 50-60% effective in preventing hospitalization and pneumonia and 80% effective in preventing death from the flu.
However, sometimes health officials do not correctly predict which flu strains will be most prevalent, and the vaccine's effectiveness is much lower for that year.
Does the flu vaccine protect against all throat, respiratory, gastrointestinal and ear infections?
The flu vaccine only protects against the three specific viral strains which are included in any given year's flu vaccine. Throat, respiratory, gastrointestinal and ear infections caused by bacteria or other kinds of viruses are not prevented by getting an annual flu shot.
Vaccination against the flu does not protect against Severe Accute Respiratory System (SARS) or the complications of SARS. The World Health Organization (WHO) is urging a worldwide flu vaccination campaign in the belief that high vaccination coverage can decrease the possibility of misdiagnosing flu as SARS and help in the early identification of a SARS outbreak. The Centers for Disease Control (CDC), however, is not recommending the flu vaccine for this purpose, since the flu vaccine is not 100 percent effective and the suggested benefits in regards to SARS cannot be reliable.
Why do doctors say I have to get a flu vaccine every year?
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 a 70-80% chance of 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.
Are there reactions to the flu vaccine?
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.
What are contraindications to the flu vaccine?
Among high risk factors listed by the CDC and the vaccine manufacturers are:
being sick with a fever
a history of Guillain-Barre Syndrome
If immunosuppressed individuals receive the flu vaccine, they may not get an adequate protective antibody response.
Is the vaccine safe during pregnancy?
In years past, pregnancy was also a contraindication to flu vaccine. 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.
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 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 with only a trace amount of thimerosal formulated for children aged 6 to 35 months 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.
Is the 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 older than 6 months of age is strongly recommended by the Advisory Committee on Immunization Practices (ACIP) of the CDC.
What about the new nasal spray flu vaccine?
A live-virus nasal flu vaccine, FluMist, was approved for use in June 2003. Its approved use is limited to healthy people between the ages of 5 and 49. This excludes its use in those considered at greatest risk from the disease -- the very young and the elderly.
Who should not receive the FluMist vaccine?
people with asthma
people with chronic lung or heart disease
people with chronic underlying medical conditions such as diabetes or kidney disorders
anyone allergic to any part of the vaccine, including eggs
children or adolescents receiving aspirin therapy
those with a history of Guillain-Barre Syndrome
people with known or suspected immune system problems or who are immune-suppressed due to treatment with steroids, chemotherapy, radiation or other immunosuppressive therapies or their close contacts
children younger than 5 and adults over 50
Due to the possibility of spreading the virus, individuals receiving the vaccine are advised to avoid close contact with immune-compromised individuals for at least 21 days.
Is FluMist safe to give with other vaccines?
No studies have shown the safety of giving FluMist along with other vaccines; therefore, it should not be given along with any other vaccine. The product manufacturer's insert advises waiting at least two weeks after receiving a killed vaccine and at least one month after receiving a live-virus vaccine (MMR, chicken pox).
How is the new 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 three weeks after receiving the vaccine.
What are the reactions to the vaccine?
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. In adults the most common side effects were runny nose, cough, sore throat, headache, muscle aches, fever, chills and tiredness or weakness. 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.
How is the vaccine made?
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 does not contain any preservatives.
For more information on the risks of this vaccine for those with immune deficiency, please visit the Immune Deficiency Foundation.
Manufacturer's Package Insert.
1. MMWR Recommendations and Reports "Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP)" April 25, 2003
2. Fluzone 2003-2004 Formula, Aventis Product information as of July 2003
3. Influenza Virus Vaccine Live, Intranasal Flumist 2003-2004 Formula, Package Insert (Circular) June 16, 2003
© National Vaccine Information Center
The National Vaccine Information Center (NVIC) is a national, non-profit educational organization founded in 1982. Located in Vienna, Virginia, the NVIC is the oldest and largest parent-led organization advocating reformation of the mass vaccination system and is responsible for launching the vaccine safety movement in America in the early 1980s. To learn more or to sign up for free e-news and newsletters, visit the NVIC web site.