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nfluenza, or flu, is a respiratory illness that results from
a viral infection. Flu is highly contagious and spreads through respiratory
droplets. A person can pass it on while talking or through physical contact,
such as shaking hands.
Influenza
A and influenza B cause seasonal epidemics in the United States and elsewhere
every winter. Type C usually causes mild respiratory illness.
Some
strains of influenza A, such as the H5N1 “bird flu” virus, occasionally infect humans,
causing serious illness. Experts track these strains carefully, as they try to
predict how they will change, and how they might affect people.
In this
article, we explain the symptoms of flu, the treatment options, how it differs
from a cold, and how to prevent the flu.
Share on PinterestA person with the flu may experience a
stuffy or runny nose.
According
to the Centers for Disease Control and Prevention (CDC), a person with
flu may experience:
- a high temperature that lasts
3–4 days
- a stuffy or runny nose
- cold sweats and shivers
- aches that may be severe
- a headache
- fatigue
Not
everyone with flu will have all of these symptoms. For instance, it is possible
to have flu without a fever.
The
symptoms of influenza typically come on suddenly. Initially, a person with
flu may experience:
- a high temperature
- a stuffy or runny nose
- a dry cough
- cold sweats and shivers
- aches that may be severe
- a headache
- fatigue, and a feeling of being
unwell
- a low appetite
Flu symptoms in adults
Adults
with the following symptoms should seek medical help urgently:
- breathing difficulties
- pain or pressure in the chest
or abdomen
- dizziness, confusion, or loss
of alertness
- seizures
- not urinating, which may
indicate dehydration
- severe pain, weakness, and
unsteadiness
- a fever or cough that goes away and then comes back
- a worsening of other existing
health conditions
Flu symptoms in children
Children
often have similar symptoms to adults but can also have gastrointestinal
symptoms, such as nausea, vomiting, and diarrhea.
If a
child has the following symptoms, they need emergency medical care:
- breathing difficulties
- rapid breathing
- bluish face or lips
- chest pain or ribs pulling
inward as they breathe
- severe aches
- dehydration, for example, not
urinating for 8 hours and crying dry tears
- lack of alertness or
interaction with others
- a fever above 104°F or any
fever in a child under 12 weeks of age
- a fever or cough that goes away
but then comes back
- a worsening of any other
medical conditions
Should
children have flu medication? Find out more here about Tamiflu and its effects on children.
Flu symptoms in babies
Flu can
be dangerous for babies.
If symptoms appear, a parent or caregiver should seek medical help.
A baby
with flu may:
- be very tired
- have a cough and sore throat
- have a stuffy or runny nose
- have a fever of 100°F or more
- have vomiting or diarrhea
The
baby needs emergency medical attention if they:
- do not want anyone to hold them
- have a blue or gray skin color
- are breathing fast or have
difficulty breathing
- have a fever with a rash
- have symptoms that go away but
come back again
- show signs of dehydration, for
example, not urinating
- do not wake up or interact
- have severe and persistent
vomiting
Flu type A symptoms
If a
person has the following symptoms, they may have influenza type A:
- fever and chills
- headache
- muscle aches
- fatigue
- weakness
- a stuffy or runny nose
- a sore throat and cough
Learn more here about influenza A.
Flu type B symptoms
Influenza
B symptoms are similar to those of influenza A.
Learn more here about influenza B.
Most
people will be able to treat the flu at home. A combination of lifestyle
remedies and over-the-counter medication can help relieve symptoms.
Pain
relief medication can help manage a headache and body pains. A healthcare
professional can recommend the best options.
Some
painkillers, such as aspirin, are not suitable for children under 16
years of age. The use of aspirin at this age can lead to a condition known as
Reye’s syndrome.
Various
options are available over the counter or to purchase online. It is important to compare different products
and only take them under the advice of a medical professional.
How
long does flu last? Find out here.
Flu medication
A virus
causes flu, so antibiotics will
not cure the illness. A doctor will only prescribe antibiotics if a bacterial
infection is present alongside the flu. However, antiviral medications may help
when someone has the flu.
Here are some tips on how to treat a
cold or flu at home.
Antivirals
aim to stop the virus from multiplying in a person’s body. Examples include
oseltamivir (Tamiflu) and zanamivir (Relenza).
In
2018, the Food and Drug Administration (FDA)
approved a new drug called baloxavir marboxil (Xofluza) for acute, uncomplicated
flu. People can take the drug by mouth in a single dose.
People
can receive this treatment if they are aged 12 years or more and have had
symptoms for fewer than 48 hours. Possible side effects include diarrhea
and bronchitis.
Some
research shows that flu medication may affect a person’s heart. Find out more here.
Flu home remedies
When a
person has flu, it is essential that they:
- stay at home
- avoid contact with other people
if possible
- keep warm and rest
- consume plenty of liquids and
healthful foods
- avoid alcohol
- stop smoking, as this raises
the risk of complications
Other
things people can try at home include:
- chicken broth
- herbal teas
- vitamin supplements
However,
there is not enough evidence available to confirm that consuming these helps.
Which foods are a good choice for a
person with flu?
If a
person seeks medical advice for flu symptoms, a doctor will likely ask about
their symptoms and do a physical examination. A doctor may also take a throat
swab for testing.
The rapid influenza diagnostic test can
produce results in 10–15 minutes but may not be accurate. Other, more accurate
tests can take longer to give results.
Flu or a cold?
Share on PinterestImage credit: Stephen Kelly, 2018.
People
often confuse the flu with a bad cold, as some symptoms are
similar.
A cold and the flu both involve:
- a runny or blocked nose
- a sore throat
- a cough
- chest discomfort
- fatigue
However,
there are some differences:
- A cold does not involve a
fever, while the flu usually does.
- The symptoms of a cold tend to
appear gradually, while flu symptoms can develop rapidly.
- Cold symptoms are typically
less severe than those of flu.
- After having the flu, a person
may continue to feel tired for several weeks.
- Flu is more likely to lead to
complications, and it can be life threatening.
Flu or food poisoning?
There
are many types of viruses, and some can affect the digestive system. People
sometimes call this “stomach flu.” This illness is different from influenza,
which is a respiratory disease.
The
most common cause of “stomach flu” is the norovirus, which enters the body through contaminated food or
drink. Symptoms include nausea, vomiting, and diarrhea. Food
poisoning causes similar symptoms.
Is it a
stomach virus or food poisoning? Find out here.
Flu or pneumonia?
Pneumonia can be bacterial or viral. The symptoms
can resemble those of flu,
but an individual may have a sharp, stabbing pain in the chest, especially when
they breathe deeply or cough.
Bacterial
pneumonia can start slowly or suddenly. Symptoms can include:
- a very high temperature
- sweating
- rapid breathing and pulse rate
- blue nailbeds due to a lack of
oxygen
Symptoms
of viral pneumonia are similar to those of the flu. They include:
- fever
- dry cough
- headache
- aches and weakness
However,
unlike the flu, symptoms of pneumonia usually develop gradually. Anyone who has
a high fever and breathing difficulties should see a doctor immediately.
What is
viral pneumonia? Find out here.
People
can have the flu at any time, but it is more common during the flu season.
The timing and duration of
the flu season change from year to year, but it usually happens around fall and
winter.
Flu
activity often starts to increase in October, and it can last as late as May.
However, it is most common from December to February.
The flu
shot can help prevent flu, but it is not 100% effective. People should follow
lifestyle measures to reduce their risk.
Lifestyle tips for avoiding flu
Tips
for avoiding infection include:
- practicing good hygiene,
including frequent hand washing
- keeping the immune system
strong by following a healthful diet
- quitting or avoiding smoking,
as smokers are more likely to develop complications
- staying away from people who
have the flu
People
should also stay away from others when they have the flu to avoid spreading it
themselves.
Click here for more information on
how to avoid flu.
The flu
virus transmits through droplets of liquid. A person can pass the virus on to
another person who is up to 6 feet away from them when they
cough, sneeze, talk, or breathe.
A
healthy individual can pass on the virus a day before they, themselves, have
symptoms. In other words, it is possible to pass on the flu before you know you
have it. The infected individual can continue to transmit the virus for up to
5–7 days after symptoms appear.
People
with a weakened immune system, older people, and young children may be able to
pass on the virus for longer than this.
Flu is
most contagious in the first 3–4 days after symptoms appear.
How
long is flu contagious? Find out here.
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A
person can develop flu symptoms if droplets that contain the virus and come
from the breath of another person enter their mouth, nose, or lungs.
This
transmission can happen if:
- Someone without the virus is
near a person with flu.
- Someone who is virus free
handles an object a person with the virus has touched and then touches
their mouth, nose, or eyes.
Research
shows that just breathing can spread the flu virus. Learn more here.
The
incubation period of a disease is the time it takes from when the virus infects
a person to when the symptoms start.
For
flu, this is around 2 days, but it
can vary from 1 to 4 days.
A
person can transmit the virus even before symptoms appear.
Flu can
be more serious during
pregnancy, as pregnancy affects how the immune system works. If a woman is
pregnant and has flu, they may need to spend time in the hospital.
Pregnancy-related
complications include a higher risk of:
- preterm birth
- low birth weight
- stillbirth
Flu can
be fatal for newborns. Risks to the mother include a greater chance of having
complications, such as bronchitis, ear and blood infections.
What
are some other causes of fever during pregnancy? Find out here.
Flu
symptoms appear suddenly, usually around 2 days after
infection. Most symptoms disappear after about 1 week, but a cough may last for
up to 2 weeks.
In some
cases, a person may still be contagious for up to 1 week after their symptoms
have disappeared.
If complications develop,
these can take longer to resolve. Some of the more severe types of
complications can have a long term impact on a person’s health, for example,
kidney failure.
Some
people experience post-viral fatigue for a week or so after the main symptoms
disappear. They may have a lingering sense of tiredness and feeling unwell.
Learn more here about post-viral
syndrome and how to manage it.
How
long does it take for a cold to pass? Find out here.
Typically, flu may progress as
follows:
- The virus infects a person,
usually through their nose or mouth.
- After one day, they may be able
to transmit the virus to others.
- Symptoms appear 1–2 days after
infection.
- The chance of transmitting the
virus is highest 3–4 days after symptoms appear.
- After 4 days, the fever and
muscle aches improve.
- After 1 week, most symptoms
disappear.
- The risk of transmitting the
virus disappears 5–7 days after symptoms appear.
- The cough and tiredness may
remain for a further week.
How
long does the flu last? Find out here.
The flu
is not usually serious, but it is unpleasant. For some people, however,
complications can arise. Some of these can be life threatening.
Complications
include:
- bacterial pneumonia
- dehydration
- worsening of chronic medical
conditions, such as congestive heart failure, asthma,
or diabetes
- sinus problems and ear
infections
The
risk of experiencing severe symptoms and flu complications is higher in the
following cases:
- adults over 65 years of age
- babies or young children
- pregnant women
- people with heart or
cardiovascular disease
- individuals with chest
problems, such as asthma or bronchitis
- people with kidney disease or
diabetes
- individuals who are taking
steroids
- people undergoing treatment
for cancer
- anyone with a weakened immune
system
Sometimes
a new type of flu will emerge, such as H5N1, or bird flu. What is bird flu, and
should we worry about it? Find out here.
The
single best way to prevent flu is to have a flu vaccination every year.
There
are two types of vaccination:
The flu shot: A healthcare
professional will administer the flu shot with a needle, usually in the arm. It
is suitable for anyone older than 6 months, including healthy people and those
with chronic medical conditions.
The nasal-spray flu vaccine: The
nasal-spray flu vaccine contains live, weakened flu viruses that do not cause
illness.
Seasonal flu shot
A flu
shot will contain the vaccine for several influenza viruses, according to
the CDC.
Examples
include:
- influenza A (H1N1) virus
- influenza (H3N2) virus
- one or two influenza B viruses
However,
viruses adapt and change over time, and scientists may need to adjust the
content of the vaccines each year.
Data
from international surveillance programs help experts predict which types are
likely to circulate in a given flu season. Protection begins about 2 weeks
after receiving the vaccination.
Seasonal
flu vaccinations should start in September or as soon as the vaccine is ready.
They continue throughout the flu season, into January and beyond.
Flu shot side effects
The CDC note that the flu vaccine has a
good safety record, and it cannot cause flu.
A person
may experience the following adverse effects after having a vaccine, but these
will be mild and usually pass within a few days.
- pain, redness, and swelling at
the injection site
- headache
- fever
- nausea
- muscle aches
Around
1–2 people in every 1 million may develop a condition known as Guillain-Barr
syndrome (GBS). However, people can also develop GBS after having flu, and the
risk of this is higher than with the vaccine. The risk of developing GBS may be
lower with the nasal spray version of the vaccine.
If
someone experiences hives,
swelling, and difficulty breathing after any vaccine, they should seek
immediate medical help as these may be the sign of an allergic reaction. A
severe reaction is known as anaphylaxis,
which can be life threatening.
Click here to find out how to
recognize anaphylaxis and what to do if it happens.
People
who have previously had an allergic reaction to a vaccine should not have the
flu shot.
Is the
flu shot safe? Find out here.
Flu shot pregnancy
It is
safe to have the flu shot during pregnancy, and doctors recommend it. It takes about 2 weeks to
provide protection. The vaccine will also pass through to the fetus and give
them some protection from the flu.
Newborns
cannot have a flu vaccine, but having flu can be dangerous for them. Having the
vaccine can benefit both the mother and her unborn child.
Flu shot effectiveness
The flu
shot cannot offer 100% protection from the flu as scientists cannot predict
precisely what flu types will circulate during a season.
CDC
figures from 2018–2019 show that the effectiveness of the vaccine in preventing
influenza A or B was about 47%.
Many factors can contribute to the
effectiveness of the flu shot from year to year. These can include the age and
overall health of the person receiving the vaccination, plus how well the
vaccine matches the prevalent viruses.
Flu shot for seniors
The
CDC recommend a flu shot for people aged
65 years or more. As people get older, they are more likely to develop
complications if they have flu.
Older
people may need a higher dose of vaccine, as their immune systems may be less
able to resist the flu virus. The vaccine cannot provide complete protection
but will reduce the risk of flu and the severity of complications.
A
2017 study looked at
data for older people in hospital with the flu during the flu season 2013–2014
in the U.S. Among those who had received the vaccine, there were lower rates of
fatality, fewer complications, and less overall time spent in an intensive care
unit.
People
who are 65 years of age or older should ask their doctor about the vaccine at
the start of each flu season. The doctor will recommend a vaccine that suits
the individual.
Flu shot cost
The
cost of a flu shot in the private sector is around $15–$24, depending on
the type.
People
should check their insurance policies to find out their cover. Medicare part
B, for example, provide for one flu shot every
flu season.
A
doctor only needs to know that a person has the flu if:
- they are already frail or have
an existing health condition
- they have a weakened immune
system
- they are infants or aged 65
years or over
- their temperature remains high
after 4–5 days
- symptoms worsen or are severe
- they become short of breath,
develop chest pain, or both
However,
anyone who has concerns about their symptoms should speak to their doctor for
further advice.
How can
you diagnose a fever at home? Find out here.
Q:
Is it really worth having the flu vaccine? It seems to me
that it does not offer much protection.
A:
Even though the flu vaccine is not 100% effective,
there are still plenty of good reasons to get one every year.
First, getting the flu vaccine reduces the chances of
becoming sick. In addition to being very unpleasant, flu can cause
complications that can be potentially serious and even require hospitalization.
Even when an infection is not serious, being sick with flu can also contribute
to lost days of work or school.
Second, the vaccine may still protect a person even if they
catch the flu. People that receive the vaccine and still get sick may have a
less severe illness.
Lastly, by getting the flu vaccine, you’re protecting groups
that cannot have the vaccination or who are susceptible to serious
complications from the flu, such as older adults, children under 6 months of
age, people with a weakened immune system, and individuals with chronic health
conditions.
Jill
Seladi-Schulman, Ph.D.Answers represent the opinions of our medical experts. All
content is strictly informational and should not be considered medical advice.
23 sourcescollapsed
Medically reviewed by Jill Seladi-Schulman, Ph.D. on November 8, 2019 — Written by Yvette Brazier
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