Influenza (cont.)
What are flu symptoms?
Typical clinical features of influenza include
- fever (usually 100° F to 103° F in adults and often even higher in
children),
- respiratory symptoms such as
- headache,
- muscle aches, and
- fatigue, sometimes extreme.
Although nausea, vomiting, and diarrhea can sometimes accompany influenza
infection, especially in children, gastrointestinal symptoms are rarely
prominent. The term "stomach flu" is a misnomer that is
sometimes used to describe gastrointestinal illnesses caused by other
microorganisms.
Most people who get the flu recover completely in one to two weeks, but some
people develop serious and potentially life-threatening medical
complications, such as pneumonia. In an average year, influenza is
associated with about 20,000 deaths nationwide and many more
hospitalizations. Flu-related complications can occur at any age; however,
the elderly and people with chronic health problems are much more likely
to develop serious complications after influenza infection than are
younger, healthier people.
Is there any treatment for the flu?
Flu vaccine
Much of the illness and death caused by influenza can be prevented by
annual influenza vaccination. Flu vaccine (influenza vaccine made from inactivated and sometimes attenuated [non-infective] virus) is specifically
recommended for those who are at high risk for developing serious
complications as a result of influenza infection. These high-risk groups
include all people aged 65 years or older and people of any age with
chronic diseases of the heart, lung or kidneys, diabetes, immunosuppression, or severe forms of anemia.
Other groups for whom
vaccine is specifically recommended are residents of nursing homes and
other chronic-care facilities housing patients of any age with chronic
medical conditions and children and teenagers who are receiving long-term
aspirin therapy and who may therefore be at risk for developing Reye
syndrome after an influenza virus infection. Influenza vaccine is also
recommended for people who are in close or frequent contact with anyone in
the high-risk groups defined above. These people include health-care
personnel and volunteers who work with high-risk patients and people who
live in a household with a high-risk person.
Because the flu is easily spread among children and because many children require hospitalization with the flu, the U.S. Centers for Disease Control and Prevention (CDC) now advises that all children ages 6 to 59 months receive a yearly flu vaccination.
Although annual influenza vaccination has long been recommended for
people in the high-risk groups, many still do not receive the vaccine.
Some people are not vaccinated because of misperceptions about influenza
and the vaccine. They mistakenly perceive influenza as merely a nuisance
and believe that the vaccine causes unpleasant side effects or that it may
even cause the flu. The truth is that influenza vaccine causes no side
effects in most people. The most serious side effect that can occur after
influenza vaccination is an allergic reaction in people who have severe
allergy to eggs, since the viruses used in the vaccine are grown in hens'
eggs. For this reason, people who have an allergy to eggs should not
receive the influenza vaccine. Also, the vaccine is not recommended while individuals have active infections or active
diseases of the nervous system.
Less than one-third of those who receive the vaccine have some soreness at
the vaccination site, and about 5% to 10% experience mild side effects,
such as headache or low-grade fever, for about a day after vaccination.
These side effects are most likely to occur in children who have not been
exposed to influenza virus in the past.
Nevertheless, some older people remember earlier influenza vaccines that
did, in fact, produce more unpleasant side effects. Vaccines produced from
the 1940s to the mid-1960s were not as highly purified as modern influenza
vaccines, and it was these impurities that caused most of the side
effects. Since the side effects associated with these early vaccines, such
as fever, headache, muscle aches and fatigue, were similar to some of the
symptoms of influenza, people believed that the vaccine had caused them to
get the flu. However, influenza vaccine produced in the United States has
never been capable of causing influenza. One type of influenza vaccine made with live attenuated influenza viruses has been developed, but this vaccine is made with viruses that can confer immunity but do not cause classic influenza symptoms.
Some people do not receive influenza vaccine because they believe it is
not very effective. There are several different reasons for this belief.
People who have received influenza vaccine may subsequently have an
illness that is mistaken for influenza, and they believe that the vaccine
failed to protect them. In other cases, people who have received the vaccine
may indeed have an influenza infection. Overall vaccine effectiveness
varies from year to year, depending upon the degree of similarity between
the influenza virus strains included in the vaccine and the strain or
strains that circulate during the influenza season. Because the vaccine
strains must be chosen nine to 10 months before the influenza season, and
because influenza viruses mutate over time, sometimes mutations occur in
the circulating virus strains between the time the vaccine strains are chosen and
the next influenza season ends. These mutations sometimes reduce the
ability of the vaccine-induced antibody to inhibit the newly mutated
virus, thereby reducing vaccine efficacy.
Vaccine efficacy also varies from one person to another. Studies of healthy young adults have shown influenza vaccine to be 70% to 90% effective in preventing illness. In the elderly and those with certain chronic medical conditions such as HIV, the vaccine is often less effective in preventing illness. Studies show the vaccine reduces hospitalization by about 70% and death by about 85% among the elderly who are not in nursing homes. Among nursing-home residents, vaccine can reduce the risk of hospitalization by about 50%, the risk of pneumonia by about 60%, and the risk of death by 75% to 80%. If antigenic drift results in changing the circulating virus from the strains used in the vaccine, vaccine efficacy may be reduced. However, the vaccine is still likely to lessen the severity of the illness and to prevent complications and death.
Next: Why must the flu vaccine be taken every year? »
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