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What Is Influenza (“Flu”)?

Iowa Health Book: Infectious Diseases

Important Information About Influenza and Influenza Vaccine (1994-1995)

Massachusetts Department of Public Health
Peer Review Status: Externally Peer Reviewed by the Massachusetts Department of Public Health
Creation Date: August 1994
Last Revision Date: August 1994


Influenza (or “flu”) is a viral infection of the nose, throat, bronchial tubes, and lungs that can make someone of any age ill. Usually the flu occurs in the United States from about November to April. If you get the flu, you usually have fever, chills, cough, and soreness and aching in your back, arms, and legs. Although most people are ill for only a few days, some persons have a much more serious illness and may need to go to the hospital. On average, thousands of people die each year in the United States from the flu or related complications.

Who Should Get Influenza Vaccine?

Because influenza is usually not life threatening in healthy individuals and most people recover fully, health officials emphasize the use of vaccine for the elderly and people with other health problems which make these individuals more likely to be seriously ill or to die from the flu or its complications. For example, people who after even light exercise become short of breath due to diseases affecting their heart or lungs, and people who have low resistance to infections, are likely to be more seriously affected by the flu. Thus, the following groups are at increased risk for serious illness with the flu and should receive vaccine:

  • All people 65 years of age or older.
  • Adults and children with long-term heart or lung problems which caused asthma to see a doctor regularly, or to be admitted to a hospital for care during the past year.
  • Residents of nursing homes, and other institutions housing patients of any age who have serious long-term health problems.
  • People of any age who during the past year have regularly seen a doctor or have been admitted to a hospital for treatment for kidney disease, cystic fibrosis, chronic metabolic disease such as diabetes, anemia (“low blood”), or severe asthma.
  • People who have a type of cancer or immunological disorder (or use certain types of medicines) that lowers the body’s normal resistance to infections. (Because influenza might cause serious illness and complications in persons infected with the HIV virus which causes AIDS, these individuals should receive influenza vaccine.)
  • Children and teenagers (6 months through 18 years of age) on long-term treatment with aspirin who, if they catch the flu, may be at risk of getting Reye’s syndrome (a childhood disease that causes coma, liver damage, and death).

Medical staff in health-care facilities should be vaccinated, to reduce the possibility that high-risk patients might catch the flu when receiving medical care. Family members or others who provide care to high-risk persons at home should also be vaccinated. The possibility for spreading the flu to high-risk persons can be reduced by vaccinating:

  • Doctors, nurses, and other personnel in both hospital and outpatient care setting.
  • Personnel of nursing homes and chronic-care facilities who have contact with patients or residents.
  • Individuals who provide care to high-risk persons at home, such as visiting nurses and volunteers, as well as all household members, including children, whether or not they are providers of care.

In addition, a flu shot may be given to:

  • Persons wishing to reduce their chances of catching the flu.
  • Persons who provide essential community services.
  • Students or other persons in schools and colleges if outbreak would cause major disruptions of school activities.
  • Persons traveling to the tropics at any time of the year or to countries south of the equator during April-September. (Persons with high-risk medical conditions and those ages 65 and older who are traveling as indicated above especially should be encouraged to receive vaccine.)

Influenza Vaccine:

The viruses that cause flu frequently change, so people who have been infected or given a flu shot in previous years may become infected with a new strain. Because of this, and because any immunity produced by the flu shot will possible decrease in the year after vaccination, persons in the high-risk groups listed above should be vaccinated every year. This year’s flu shot contains viruses representing the A/Texas/36/91, A/Shangdong/9/93 (H3N2) and B/Panama/45/90 strains, which are thought to be most likely to occur in the United States next winter. All the viruses in the vaccine are killed so they cannot infect anyone. Vaccine will begin to provide its protective effect after about one or two weeks, and immunity may decrease, on average, after several months. Flu shots will not fully protect all persons who get them against the flu. They also will not protect against other illnesses that resemble the flu.


Only a single flu shot is needed each season for persons 9 years of age and older, but children 8 years of age or younger may need a second shot after a month. The doctor or nurse giving the flu shot will discuss this with parents or guardians. Children less than 13 years old should be given only vaccine that has been chemically treated during manufacture (split virus) to reduce chances of any side effects. Split-virus vaccines can also be used by adults.

Possible Side Effects From the Vaccine:

Most people have no side effects from recent influenza vaccines. Flu shots are given by injection, usually into a muscle of the upper arm. This may cause soreness for a day or two at the injection site and occasionally may also cause a fever or achiness for one or two days. Unlike the 1976 swine flu vaccine, recent flu shots have not been clearly linked to the paralytic illness Guillain-Barre syndrome (GBS). In 1990-1 there may have been a small increase in GBS cases in vaccinated persons 18 to 64 years of age, but not in those 65 or older. This possible association with GBS was not as convincing as with the swine flu vaccine. Even if GBS was a true side effect, the very low estimated risk of getting GBS is less than that of getting severe influenza that could be prevented by vaccine. As is the case with most drugs or vaccines, there is a possibility that allergic or more serious reactions, even death, could occur with the flu shot.

Simultaneous Use of Other Vaccines:

The target group for influenza and pneumococcal vaccination overlap. Both vaccines can be given at the same time at different sites without increasing side effects. High-risk children may also receive influenza vaccine at the same time as measles, mumps, rubella, Haemophilus influenzae type b, pneumococcal, poliovirus vaccines, diphtheria and tetanus toxoids, and pertussis adsorbed and acellular pertussis vaccines, but at different sites.

Warning! Some People Should Check With A Doctor Before Taking Influenza Vaccine:

  • Persons with an allergy to eggs that causes a dangerous reaction if they eat eggs and those who have had a serious reaction to previous influenza vaccination should consult a physician before receiving the vaccine.
  • Anyone who has ever been paralyzed with Guillain-Barre syndrome should seek advice from their doctor about special risks that might exist in their cases.
  • Women who are or might be pregnant should consult with their doctor.
  • Persons who are ill and have a fever should ask their doctor whether or not they should delay vaccination until the fever and other temporary symptoms have gone.


If you have any questions about influenza or influenza vaccination please ask now or call your doctor before requesting the vaccine.


If anyone receiving influenza vaccine gets sick, visits a doctor, hospital, or clinic in the four weeks after vaccination, please report this to:

Vaccine Adverse Event Reporting System
Massachusetts Immunization Program
(617) 522-3700 x420

Vaccine Administration Record

The doctor or clinic may use a form for the required written documentation, or they may record it in your or your child’s medical record. They will record what vaccine was given, when the vaccine was given, the name of the company that made the vaccine, the vaccine’s special lot number, the name and title of the person who gave the vaccine and the address where the vaccine was given, the document number and the date printed on the Important Information Statement (IIS) and the date the IIS was given to you.

Please note: obtaining the signature of the patient, parent or legal representative is now optional.

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