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The flu season will be upon us before long, so I thought I would discuss influenza A this month. Influenza A is a common viral infection that is commonly referred to as the "flu." It has been around for years and sends fear through our spines when we hear it is going around. This fear is based on the deaths that it causes every year and the time that is lost from work. The worst epidemic was in 1918-1919 when over 500,000 people died in the United States and twenty million people died worldwide. Deaths are usually caused by complications of the flu, such as pneumonia. Healthy individuals rarely die of the flu, but they may be fairly miserable for up to a week or so. Usually, about 36,000 people die every year from complications of the flu. Flu epidemics usually occur from December through February, but several years ago it started in September. In any given year about ten to twenty percent of the population will become infected. Approximately 1 % of those infected will need to be hospitalized and 8 % of those hospitalized will die. Influenza accounts for millions of days lost from work each year.


Influenza A is caused by a virus that is able to change slightly from year to year so that a new vaccine has to be given every year to maintain protection. Viruses are very small germs that are much smaller than bacteria. Viruses are responsible for the bulk of colds and other childhood illnesses. Bacteria cause illnesses like "strep throat," ear infections and sinusitis. There are several strains of Influenza A that commonly cause the "flu." Influenza B is also responsible for a flu-like illness, but it is not as severe as the Influenza A strain. The so-called stomach flu has nothing to do with influenza A. Stomach flu is a viral infection that causes nausea, vomiting and diarrhea.


The symptoms of Influenza A are fairly typical and initially consist of:
Muscle aches
Profound weakness
Sore throat
Dry cough
Pleuritic pain (pain in the chest when coughing)
Influenza is spread from person to person by direct contact, large droplet infection, or articles recently contaminated by nasal secretions. People are infectious from 24 hours before the onset of symptoms until about 7 days after the infection starts. The incubation period is 1-2 days. Many cold viruses cause very similar symptoms but not usually as severe. Flu almost always occurs in the winter months and associated with an epidemic. If you get the above symptoms and the flu has not been reported it would be extremely unlikely to be influenza A. We usually have a several month advanced notice that the flu is starting in the United States.


Common complications of influenza are pneumonia, ear infections, sinusitis and bronchitis. Less common complications are Reye's syndrome, Guillain-Barre syndrome and severe inflammation of the heart muscle.


Treatment of influenza is generally symptomatic, meaning plenty of fluids, bed rest and acetaminophen (Tylenol). Aspirin should not be given to children because it increases the chances of getting Reye's syndrome which is a potentially fatal complication of influenza. Antibiotics are totally ineffective against the flu. They may be prescribed to treat secondary bacterial complications of the flu. There are several antiviral agents that can be used to actually treat influenza. They are amantidine, oseltamvir and rimantadine. Unfortunately, they must be started within 48 hours of the onset of influenza symptoms or they are not effective. Most patients don't come in until after they have had the symptoms for several days. This is one case where a person cannot come in too early to be treated. These antiviral agents can shorten the course of the illness as well as reduce complications. The vaccine for influenza is about 70 % to 80 % effective.
It must be given every year since different strains tend to go around each year and we don't seem to be able to maintain protective antibodies for over several years. It takes about 2 weeks for our bodies to develop protection from influenza after being given the vaccine, so we can't wait until the epidemic is upon us to get immunized. I usually recommend that patients get immunized in October.
A nasal spray flu vaccine is now available for prevention of flu in healthy individuals six to 49 years of age. It costs about $70.

Side Effects of the Flu Shot

Significant side effects of the flu shot are unusual and generally mild. Pain at the site of injection is the most common, followed by fatigue, muscle aches and fever. In spite of what is commonly said, the flu shot is totally incapable of causing the "flu." The vaccine is composed of dead particles of the influenza virus and is incapable of causing infection. When you develop a "cold-like" illness following vaccination it is purely a coincidence. This also could be related to individuals getting the vaccine after the epidemic has already started, and they are incubating the virus at the time they get the vaccine. Since it takes 2 weeks for the vaccine to be effective, they would not be protected at all and certainly could get the flu. They could also just be getting a cold at the time they get the vaccine. The worst side effect of the vaccine is an allergic reaction to the vaccine which can be fatal, although it is extremely rare. It is related to being allergic to eggs which can be present in the vaccine since it is made using eggs. People that are extremely allergic to eggs should not get the influenza vaccine. Since thimerosal is used as a preservative, anyone allergic to this compound should not have a flu shot. A study in the New England Journal of Medicine, showed that the side effects of a flu shot are almost identical to the side effects of a placebo injection, with the exception of arm soreness which was higher in the individuals that actually received the flu shot.

The flu vaccine is recommended for the following individuals:

Persons age 50 or older.
Adults and children with chronic disorders of the pulmonary or cardiovascular systems.
Residents of nursing homes or chronic care facilities.
Children and teenagers who are receiving long-term aspirin therapy and therefore would be at increased risk of developing Reye's syndrome.
Adults and children who have required regular medical follow-up or hospitalization during the preceding year because of chronic metabolic diseases such as diabetes, renal dysfunction, hemoglobinopathies or immunosuppression.
Physicians, nurses and any other individuals who work around patients or residents of a chronic care facility.
Household members of high risk patients.
Household members who live with an infant under six months of age.
Any individuals who wish to reduce their chances of acquiring influenza infection.
Persons that provide essential community services may be considered for vaccination to minimize disruption of essential activities.
Women who will be in the second or third trimester of pregnancy during the flu season.
Infants six to twenty-three months of age.

Benefits of the Vaccine

A study in the New England Journal of Medicine showed that getting the flu shot will:
Reduce the number of doctor visits for "colds" by 44%.
Reduce sick days from work by 43%.
Reduce the total number of reported "colds" by 25%.
Save an average of $46.85 per flu shot given.


1. Centers for Disease Control and Prevention. 2004-05 Flu Vaccine Shortage: Interim Influenza Vaccination Recommendations—2004-05 Influenza Season. Available at: http://www.cdc.gov/flu/protect/0405shortage.htm.
2. Merigan TC: Influenza. Scientific American-Medicine 7, XXV: p 2-7.
3. Nichol KL, et al. The Effectiveness of Vaccination Against Influenza In Healthy, Working Adults. N Engl J Med 1995 333: 889-893.
4. Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA. 2003;289:179-186.

The information provided above is offered as a community service about health-care issues and is not a substitute for individual consultation. Advice on individual problems should be obtained from your personal physician. This information is based on research by the author and represents his interpretation of the literature.

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Readers may send questions to our email address. This column is for informational purposes only and is not a substitute for professional or medical advice.

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