Key facts about influenza
(flu) and flu vaccine
What is influenza (also called flu)?
The flu is a contagious respiratory illness
caused by influenza viruses that infect the
nose, throat, and lungs. It can cause mild to
severe illness, and at times can lead to death.
The best way to prevent the flu is by getting a
flu vaccine each year.
Signs and symptoms of flu
People who have the flu often feel some or
all of these signs and symptoms:
- Fever* or feeling
feverish/chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches
- Fatigue (very tired)
- Some people may have
vomiting and diarrhea, though
this is more common in children
than adults.
*It’s important to note that not everyone
with flu will have a fever.
How flu spreads
Most experts believe that flu viruses spread
mainly by droplets made when people with flu
cough, sneeze or talk. These droplets can land
in the mouths or noses of people who are nearby.
Less often, a person might also get flu by
touching a surface or object that has flu virus
on it and then touching their own mouth, eyes or
possibly their nose.
Period of contagiousness
You may be able to pass on the flu to someone
else before you know you are sick, as well as
while you are sick. Most healthy adults may be
able to infect others beginning one day
before symptoms develop and up to 5 to
7 days after becoming sick.
Some people, especially young children and
people with weakened immune systems, might be
able to infect others for an even longer time.
How serious is the flu?
Flu is unpredictable and how severe it is can
vary widely from one season to the next
depending on many things, including:
- what flu viruses are
spreading,
- how much flu vaccine is
available
- when vaccine is available
- how many people get
vaccinated, and
- how well the flu vaccine is
matched to flu viruses that are
causing illness.
Certain people are
at greater risk for serious complications if
they get the flu. This includes older people,
young children, pregnant women and people with
certain health conditions (such as asthma,
diabetes, or heart disease), and persons who
live in facilities like nursing homes.
Flu seasons are unpredictable and can be
severe. Over a period of 30 years, between 1976
and 2006, estimates of flu-associated deaths in
the United States range from a low of about
3,000 to a high of about 49,000 people.
Complications of flu
Complications of flu can include bacterial
pneumonia, ear infections, sinus infections,
dehydration, and worsening of chronic medical
conditions, such as congestive heart failure,
asthma, or diabetes.
Preventing seasonal flu: Get vaccinated
The single best way to prevent the flu is to
get a flu vaccine each season. There are two
types of flu vaccines:
- "Flu shots" — inactivated
vaccines (containing killed
virus) that are given with a
needle. There are three flu
shots being produced for the
United States market now.
- The regular
seasonal flu
shot is
"intramuscular"
which means it
is injected into
muscle (usually
in the upper
arm). It has
been used for
decades and is
approved for use
in people six
months of age
and older,
including
healthy people,
people with
chronic medical
conditions and
pregnant women.
Regular flu
shots make up
the bulk of the
vaccine supply
produced for the
United States.
- A hi-dose
vaccine for
people 65 and
older which also
is
intramuscular.
This vaccine was
first made
available during
the 2010-2011
season.
- An
intradermal
vaccine for
people 18 to 64
years of age
which is
injected with a
needle into the
"dermis" or
skin. This
vaccine is being
made available
for the first
time for the
2011-2012
season.
- The nasal-spray flu vaccine
— a vaccine made with live,
weakened flu viruses that is
given as a nasal spray
(sometimes called LAIV for "Live
Attenuated Influenza Vaccine").
The viruses in the nasal spray
vaccine do not cause the flu.
LAIV is approved for use in
healthy* people two to 49 years of
age who are not pregnant.
About two weeks after vaccination, antibodies
develop that protect against influenza virus
infection. Flu vaccines will not protect against
flu-like illnesses caused by non-influenza
viruses.
The seasonal flu vaccine protects against the
three influenza viruses that research suggests
will be most common.
When to get vaccinated against seasonal flu
Yearly flu vaccination should begin in
September, or as soon as vaccine is available,
and continue throughout the flu season which can
last as late as May. This is because the timing
and duration of flu seasons vary. While flu
season can begin early as October, most of the
time seasonal flu activity peaks in January,
February or later.
Who should get vaccinated?
Everyone six months
and older should get a flu vaccine each year.
This recommendation has been in place since
February 24, 2010 when CDC’s Advisory Committee
on Immunization Practices (ACIP) voted for
"universal" flu vaccination in the U.S. to
expand protection against the flu to more
people. While everyone should get a flu vaccine
each flu season, it’s especially important that
certain people get vaccinated either because
they are at high risk of having serious
flu-related complications or because they live
with or care for people at high risk for
developing flu-related complications.
Who is at high risk for developing
flu-related complications?
- Children younger than five, but
especially children younger than
2-years old
-
Adults 65 years of age and older
-
Pregnant women
- American Indians and Alaskan
Natives seem to be at higher
risk of flu complications
-
People who have medical
conditions including:
-
Asthma (even
if it’s
controlled or
mild)
- Neurological
and
neurodevelopmental
conditions
[including
disorders of the
brain, spinal
cord, peripheral
nerve, and
muscle such as
cerebral palsy,
epilepsy
(seizure
disorders),
stroke,
intellectual
disability
(mental
retardation),
moderate to
severe
developmental
delay, muscular
dystrophy, or
spinal cord
injury]
- Chronic lung
disease (such as
chronic
obstructive
pulmonary
disease [COPD]
and cystic
fibrosis)
-
Heart disease
(such as
congenital heart
disease,
congestive heart
failure and
coronary artery
disease)
- Blood
disorders (such
as sickle cell
disease)
-
Endocrine
disorders (such
as
diabetes
mellitus)
- Kidney
disorders
- Liver
disorders
- Metabolic
disorders (such
as inherited
metabolic
disorders and
mitochondrial
disorders)
-
Weakened immune
system due to
disease or
medication (such
as people with
HIV or AIDS,
or cancer, or
those on chronic
steroids)
- People
younger than 19
years of age who
are receiving
long-term
aspirin therapy
- People who
are morbidly
obese (Body Mass
Index [BMI] of
40 or greater)
Who else should get vaccinated?
Other people for whom vaccination is
especially important are:
- People who live in nursing
homes and other long-term care
facilities
- People who live with or care
for those at high risk for
complications from flu,
including:
- Health care
workers
- Household
contacts of
persons at high
risk for
complications
from the flu
- Household
contacts and
caregivers of
children younger
than five years of
age with
particular
emphasis on
vaccinating
contacts of
children younger
than six months of
age (children
younger than six
months are at
highest risk of
flu-related
complications
but are too
young to get
vaccinated)
Use of the nasal spray seasonal flu vaccine
Vaccination with the nasal-spray flu vaccine
is an option for healthy* people two to 49 years
of age who are not pregnant. Even people who
live with or care for those in a high risk group
(including health care workers) can get the
nasal-spray flu vaccine as long as they are
healthy themselves and are not pregnant. The one
exception is health care workers who care for
people with severely weakened immune systems who
require a protected hospital environment; these
people should get the inactivated flu vaccine
(flu shot).
Who should not be vaccinated against
seasonal flu?
Some people should not be vaccinated without
first consulting a physician. They include:
- People who have a severe
allergy to chicken eggs.
- People who have had a severe
reaction to an influenza
vaccination in the past.
- Children younger than six
months of age (influenza vaccine
is not approved for use in this
age group).
- People who have a moderate
or severe illness with a fever
should wait to get vaccinated
until their symptoms lessen.
-
People with a history of
Guillain-Barré Syndrome (a
severe paralytic illness, also
called GBS) that occurred after
receiving influenza vaccine and
who are not at risk for severe
illness from influenza should
generally not receive vaccine.
Tell your doctor if you ever had
Guillain-Barré Syndrome. Your
doctor will help you decide
whether the vaccine is
recommended for you.
If you have questions about whether you
should get a flu vaccine, consult your health
care provider.
For more about preventing the flu, see the following: