It is caused by the influenza virus, which can be spread by coughing,
sneezing, or nasal secretions. Other illnesses can have the same symptoms and
mistaken for influenza. But only an illness caused by the influenza virus is
Anyone can get influenza, but rates of infection are highest among children.
For most people, it lasts only a few days.
It can cause:
Some people get much sicker. Influenza can lead to pneumonia and can be
dangerous for people with heart or breathing conditions. It can cause high
fever, diarrhea and seizures in children. On average, 226,000 people are
hospitalized every year because of influenza and 36,000 die – mostly
Influenza vaccine can prevent influenza.
2. Inactivated influenza vaccine.
There are two types of influenza vaccine:
Inactivated (killed) vaccine, or the “flu shot” is given by injection into
Live, attenuated (weakened) influenza vaccine is sprayed into the nostrils.
This vaccine is described in a separate Vaccine Information Statement.
Influenza viruses are always changing. Because of this, influenza vaccines
are updated every year, and an annual vaccination is recommended.
Each year scientists try to match the viruses in the vaccine to those most
likely to cause flu that year. When there is a close match the vaccine protects
most people from serious influenza related illness. But even when the there is
not a close match, the vaccine provides some protection. Influenza vaccine will
not prevent “influenza-like” illnesses caused by other viruses.
It takes up to 2 weeks for protection to develop after the shot. Protection
lasts up to a year.
Some inactivated influenza vaccine contains a preservative called
thimerosal. Some people have suggested that thimerosal may be related to
developmental problems in children. In 2004 the Institute of Medicine reviewed
many studies looking into this theory and concluded that there is no evidence
of such a relationship. Thimerosal-free influenza vaccine is available.
3. Who should get inactivated influenza vaccine?
All children 6 months and older and all older adults:
All children from 6 months through 18 years of age.
Anyone 50 years of age or older.
Anyone who is at risk of complications from influenza, or
more likely to require medical care:
Women who will be pregnant during influenza season.
Anyone with long-term health problems with:
metabolic disease, such as diabetes
anemia, and other blood disorders
Anyone with a weakened immune system due to:
HIV/AIDS or other diseases affecting the immune system
long-term treatment with drugs such as steroids
cancer treatment with x-rays or drugs
Anyone with certain muscle or nerve disorders (such as seizure disorders or
cerebral palsy) that can lead to breathing or swallowing problems.
Anyone 6 months through 18 years of age on long-term aspirin treatment
(they could develop Reye Syndrome if they got influenza).
Residents of nursing homes and other chronic-care facilities.
Anyone who lives with or cares for people at high risk for
Health care providers.
Household contacts and caregivers of children from birth up to 5 years of
Household contacts and caregivers of
people 50 years and older, or
anyone with medical conditions that put them at higher risk for severe
complications from influenza.