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Questions & Answers
What is the best way to prevent
influenza?
The best way to prevent influenza is with annual vaccination.
Is there an alternative to
vaccination in preventing influenza?
Vaccination is the principal means of preventing influenza and its
complications. Here are some additional steps that may help prevent the spread
of respiratory illnesses like influenza:
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Cover your nose and mouth with your sleeve or a tissue when you cough or sneeze—throw
the tissue away after you use it.
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Wash your hands often with soap and water, especially after you cough or sneeze.
If you are not near water, use an alcohol-based hand cleaner.
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Stay away as much as you can from people who are sick.
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If you get influenza, stay home from work or school for at least 24 hours after
the fever has ended. If you are sick, don't
go near other people to avoid infecting them.
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Try not to touch your eyes, nose, or mouth. Germs often spread this way.
What other drugs are available to prevent or treat influenza?
There are four antiviral agents approved for preventing or treating influenza in
selected patients. Only two, oseltamivir and
zanamivir, will offer protection against both A and B viruses; the other two,
amantadine and rimantadine, protect only
against the A viruses. Their use is generally limited to situations where an
outbreak is underway and immediate protection of
vulnerable, unvaccinated people is critical (e.g., nursing home residents) or in
people who are expected to have an
inadequate antibody response to the vaccine (e.g., people infected with HIV) or
who could not otherwise be vaccinated (e.g.,
people with severe egg allergies). Antiviral agents are not a substitute for
vaccination. (Note: Recent evidence indicates
that a high proportion of currently circulating influenza A viruses in the
United States have developed resistance to
amantadine and rimantadine and researchers are watching for additional antiviral
resistance to any of these four agents that
might develop in the future.)
If I contract influenza, what should I do?
Call your healthcare provider to discuss your particular situation. You will
need to get plenty of rest and drink a lot of
liquids. You can take medications to relieve the symptoms of influenza (but
never give aspirin to children or teenagers who
have influenza-like symptoms, particularly fever). If you are at high risk of
developing complications from influenza, you
should consult your healthcare provider immediately if you develop
influenza-like symptoms. For purposes of treatment and
prevention (chemoprophylaxis), antiviral medicines are prioritized for people at
high risk for influenza-related
complications, such as people 65 years or older, people with chronic medical
conditions, pregnant women, and young children.
When is a person with influenza contagious?
A person is most likely to pass on the virus during the period beginning one to
two days before the onset of symptoms and
ending four to five days after the onset.
Can you get influenza more than once?
Yes. Influenza viruses change frequently and infection with one strain does not
provide protection against all strains.
When did influenza vaccine first become available?
The first influenza vaccine in the United States became available in 1945.
What kind of vaccine is it?
There are two types of influenza vaccine. The most common influenza vaccine is
made from inactivated (killed) viruses. In
June 2003, a live virus influenza vaccine was licensed. It contains live viruses
that have been weakened (attenuated).
How are the vaccines made?
Every year, researchers and manufacturers develop a vaccine that contains virus
strains they believe will be circulating in
the upcoming influenza season. Influenza vaccine typically contains both type A
and type B viruses. The viruses selected for
the vaccine are grown in chicken eggs.
For the inactivated (injectable) vaccine, the viruses are killed with
formaldehyde, purified, and packaged in vials or
syringes. Live virus vaccine is packaged in a special nasal sprayer. About six
months are required to produce influenza
vaccine each year.
How is the vaccine given?
The inactivated vaccine is generally given as an intramuscular injection; one
product can be given as an intradermal
injection with a micro needle into the skin of the arm for persons ages 18
through 64 years. The live attenuated vaccine is
sprayed into the nose.
Who should get influenza vaccine?
Beginning with the 2010–11 vaccination season, the recommendations were expanded
to vaccinate all people ages 6 months and
older who do not have a contraindication to the vaccine.
What are the unique features of giving influenza vaccine to children compared
with adults?
Children ages 6 months through 8 years should receive two doses of influenza
vaccine the first time they receive this
vaccine, separated by at least 4 weeks. For the 2011–12 season, children through
age 8 years who did not receive at least one
dose of influenza vaccine during the 2010–11 season should also get two doses.
Who recommends the influenza vaccine?
The Centers for Disease Control and Prevention (CDC), the American Academy of
Pediatrics (AAP), the American Academy of
Family Physicians (AAFP), the American College of Physicians (ACP), and the
American College of Obstetricians and
Gynecologists (ACOG) all recommend this vaccine.
How often should this vaccine be given?
Influenza vaccine is given each year because immunity decreases after a year and
because each year's vaccine is formulated to
prevent only that year's anticipated influenza viruses.
When should people be vaccinated?
Health experts recommend that patients may be vaccinated as soon as vaccine is
available in their clinic, which can be as
early as August or September. Vaccination should continue into the winter and
spring, even until April or May. Travelers
should be aware that the influenza season typically occurs from April to
September in the Southern Hemisphere and throughout
the year in the tropics. If they missed vaccination in the previous season, they
should still be vaccinated before they
travel, even if it's in the following spring or summer.
Are there recommendations for the prevention of influenza outbreaks in
institutions?
The most important factor in preventing outbreaks is annual vaccination of all
occupants of the facility and all people
working or volunteering in the facility who share the same air as the high-risk
occupants. Groups that should be targeted
include physicians, nurses, and all other personnel in hospitals, long-term care
facilities, other care facilities, and
outpatient settings who have contact with high-risk patients in all age groups.
Should siblings of a person with a chronic illness receive influenza vaccine
even though the chronically ill person has been
vaccinated?
Yes. Vaccination is recommended for all people ages 6 months and older. This
includes all household contacts of people with
"high-risk" conditions. Either inactivated or live virus vaccine may be used; it
is preferred that the inactivated vaccine be
used for household contacts and caregivers of people with severe
immunosuppression that must be in protective isolation.
Should siblings of a healthy child who is younger than age 6 months be
vaccinated?
Yes, it is especially important that all household contacts of children too
young to be vaccinated against influenza (i.e.,
younger than age 6 months) receive annual influenza vaccination to protect the
infant from serious infection. This is very
important because these infants are too young to be vaccinated and are most
vulnerable to complications from influenza.
Is it safe for pregnant women to get influenza vaccine?
Yes. In fact, vaccination with the inactivated vaccine is recommended for women
who will be pregnant during the influenza
season. Pregnant women are at increased risk for serious medical complications
from influenza. One recent study found that
the risk of influenza-related hospitalization was four times higher in healthy
pregnant women in the fourteenth week of
pregnancy or later than in nonpregnant women. In addition, vaccination of the
mother will provide some protection for her
newborn infant. An increased risk of severe influenza infections was also
observed in postpartum women (those who delivered
within the previous 2 weeks) during the 2009–2010 H1N1 pandemic.
The live intranasal vaccine is not licensed for use in pregnant women. However,
pregnant women do not need to avoid contact
with people recently vaccinated with this vaccine.
Vaccination is especially important for all people, including breastfeeding
mothers, who are contacts of infants or children
from birth through age 59 months because infants and young children are at
higher risk for influenza complications and are
more likely to require medical care or hospitalization if infected. Women who
are breastfeeding may receive either type of
influenza vaccine unless the vaccine is not appropriate because of other medical
conditions.
How safe is this vaccine?
Influenza vaccine is very safe. The most common side effects of the injectable
(inactivated) influenza vaccine include
soreness, redness, or swelling at the site of the injection. These reactions are
temporary and occur in 15%–20% of
recipients. Less than 1% of vaccine recipients develop symptoms such as fever,
chills, and muscle aches for 1 to 2 days
following the vaccination. These symptoms are more likely to occur in a person
who has never been exposed to the influenza
virus or vaccine. Experiencing these non-specific side effects does not mean
that you are getting influenza.
Healthy children ages 2 through 4 years who received the live attenuated virus
(nasal spray) vaccine during clinical trials
appeared to have an increased chance of wheezing. Consequently, children with a
history of recurrent wheezing or have had a
wheezing episode within the past 12 months are not recommended to receive the
live nasal spray vaccine; instead, they should
be given the inactivated (injectable) vaccine.
Healthy adults receiving the live influenza vaccine reported symptoms such as
cough, runny nose, sore throat, chills, and
tiredness at a rate 3%–18% higher than for placebo recipients. There was no
increase in the occurrence of fever.
Serious adverse reactions to either vaccine are very rare. Such reactions are
most likely the result of an allergy to a
vaccine component, such as the egg protein left in the vaccine after growing the
virus. In 1976, the swine flu (injectable)
vaccine was associated with a severe illness called Guillain-Barré syndrome (GBS),
a nerve condition that can result in temporary paralysis. Injectable influenza vaccines since then have not been
clearly linked with GBS, because the disease is
so rare it is difficult to obtain a precise estimate of any increase in risk.
However, as a precaution, any person without a
high risk medical condition who previously experienced GBS within 6 weeks of an
influenza vaccination should generally not be
vaccinated. Instead, their physician may consider using antiviral drugs during
the time of potential exposure to influenza.
What can you tell me about the preservative thimerosal that is in some
injectable influenza vaccines and the claim that it
might be associated with the development of autism?
Thimerosal is a very effective preservative that has been used to prevent
bacterial contamination in vaccines for more than
50 years. It is comprised of a type of mercury known as ethylmercury. It is
different from methylmercury, which is the form
that is in fish and seafood. At very high levels, methylmercury can be toxic to
people, especially to the neurological
development of infants.
In recent years, several very large scientific studies have determined that
thimerosal in vaccines does not lead to serious
neurologic problems, including autism. Nonetheless, because we generally try to
reduce people's exposure to mercury if at all
possible, the vaccine manufacturers have voluntarily changed their production
methods to produce vaccines that are now free
of thimerosal or have only trace amounts. They have done this because it is
possible to do, not because there was any
evidence that the thimerosal was harmful.
How effective is influenza vaccine?
Protection from influenza vaccine varies by the similarity of the vaccine
strain(s) to the circulating strains, and the age
and health of the recipient. Healthy people younger than age 65 years are more
likely to have protection from their influenza
vaccination than are older, frail individuals. It is important to understand
that although the vaccine is not as effective in
preventing influenza disease among the elderly, it is effective in preventing
complications and death. In general, the
immunity following influenza vaccination rarely lasts longer than a year.
When the "match" between vaccine and circulating strains is close, the
injectable (inactivated) vaccine prevents influenza in
about 50%–70% of healthy people younger than age 65 years. Among elderly nursing
home residents, the shot is most effective
in preventing severe illness, secondary complications, and deaths related to
influenza.
In one large study among children ages 15–85 months, the live, attenuated
(nasal-spray) influenza vaccine reduced the chance
of influenza illness by 92% compared with the placebo.
Can the vaccine cause influenza?
No! Neither the injectable (inactivated) vaccine nor the live attenuated (nasal
spray) vaccine can cause influenza. The
injectable influenza vaccine contains only killed viruses and cannot cause
influenza disease. Fewer than 1% of people who are
vaccinated develop influenza-like symptoms, such as mild fever and muscle aches,
after vaccination. These side effects are
not the same as having the actual disease. The nasal spray influenza vaccine
contains live attenuated (weakened) viruses that
can produce mild symptoms similar to a cold. While the viruses are able to
replicate in the nose and throat tissue and
produce protective immunity, they are attenuated and do not replicate
effectively in the lung. Consequently, they cannot
produce influenza disease.
Protective immunity develops 1 to 2 weeks after vaccination. It is always
possible that a recently vaccinated person can be
exposed to influenza disease before their antibodies are formed and consequently
develop disease. This can result in someone
erroneously believing they developed the disease from the vaccination.
Also, to many people "the flu" is any illness with fever and cold symptoms. If
they get any viral illness, they may blame it
on the influenza vaccination or think they got "the flu" despite being
vaccinated. Influenza vaccine only protects against
certain influenza viruses, not all viruses.
Who should NOT receive influenza vaccine?
In general, the inactivated (injectable) influenza vaccine can be given to most
everyone except children younger than age 6
months, people with a history of a severe allergic reaction to eggs, or to a
previous dose of influenza vaccine (see
additional contraindications below). The live, attenuated (nasal spray)
influenza vaccine is licensed for use only in
healthy, nonpregnant individuals ages 2 through 49 years.
The following people should not be vaccinated with the live, attenuated virus
(nasal spray) influenza vaccine; however, most
(except infants younger than 6 months) can be vaccinated with the injectable
vaccine:
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People younger than age two years
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People age 50 years or older
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People with chronic pulmonary (including asthma) or cardiovascular (excluding
hypertension) diseases; people with renal,
hepatic, cognitive, neurologic/neuromuscular, hematologic, or metabolic (e.g.,
diabetes) disorders; or people with
immunosuppression, including that caused by medications or HIV
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Children ages 2 through 4 years with a history of recurrent wheezing or who
have had a wheezing episode in the last 12
months
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Children or adolescents receiving long-term aspirin therapy
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Pregnant women (adolescents or
adults).
Healthcare workers, household members, and others who have close contact with
severely immunocompromised individuals during
the periods in which the immunosuppressed person requires care in protective
isolation should preferably receive the
injectable vaccine over the live (nasal spray) vaccine. People having had a
serious allergic reaction to eggs or to a
previous dose of influenza vaccine should not receive either type of influenza
vaccine (injectable or nasal spray). People
with a history of serious egg allergies who are at increased risk for influenza
or its complications should consult with
their healthcare provider regarding referral to an allergist to determine if the
vaccine can be given following treatment for
desensitization.
People with a history of Guillain-Barré syndrome should also consult with their
physician before receiving this vaccine, so
that the potential risks and benefits of influenza immunization can be weighed.
People who are moderately or severely ill at
the time of their influenza vaccination appointment should usually wait until
their symptoms are improved before getting the
vaccine.
Some people believe they are allergic to thimerosal, the preservative used in
some brands of influenza vaccine, because in
the past they developed eye irritation after using eye drops containing
thimerosal. Past eye irritation is not a valid reason
to avoid getting influenza vaccine. Only serious, life-threatening allergies to
thimerosal are reasons not to be vaccinated
with an influenza vaccine containing thimerosal. Most brands of influenza
vaccine are packaged in vials or syringes that
contain natural rubber or latex. People with a severe allergy to latex generally
should not receive vaccine packaged in these
vials or syringes.
Questions and answers
about influenza disease
Technically reviewed by the Centers for Disease
Control and Prevention, December 2011
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