Influenza, or flu, is a respiratory illness caused by a virus. Flu is highly contagious and is normally spread by the coughs and sneezes of an infected person. Although unpleasant, flu is rarely life-threatening.

You can also catch flu by touching an infected person, for instance, shaking hands. Adults are contagious 1-2 days before getting symptoms and up to 7 days after becoming ill. This means that you can spread the influenza virus before you even know you are infected.

In this article, we explain the symptoms of flu, how it is treated, how it differs from a cold, and the best ways to prevent flu occurring.

Fast facts on fluHere are some key points about flu. More detail and supporting information is in the main article.

  • Antibiotics cannot be used to treat flu.
  • Approximately 5-20 percent of Americans will develop flu.
  • Experts agree that the best way to prevent flu is to get vaccinated each year.
  • The flu vaccine is not suitable for certain groups of people, such as those who have a severe allergy to chicken eggs.


Flu can be uncomfortable, but it is rarely life-threatening.

Confusing flu with a bad cold is common. Flu and cold symptoms may both include a runny/blocked nose, sore throat, and cough.

To help you tell them apart, below are some symptoms of flu that are different from a heavy cold:

  • high temperature
  • cold sweats and shivers
  • headache
  • aching joints and limbs
  • fatigue, feeling exhausted

There may also be gastrointestinal symptoms, such as nausea, vomiting, and diarrhea; these are much more common among children than adults.

Normally, symptoms linger for about 1 week. However, the feeling of tiredness and gloom can continue for several weeks.

It is worth noting that not every person with flu will have all of the symptoms; for instance, it is possible to have flu without fever.

Early symptoms of flu

Often, fatigue is one of the earliest signs of flu and cold. With flu, the fatigue is often more extreme. Other early symptoms can include cough, sore throat, fever, body ache, chills, and gastrointestinal changes.


As flu is caused by a virus, antibiotics cannot help, unless the flu has led to another illness caused by bacteria. Antivirals, such as oseltamivir (Tamiflu) and zanamivir (Relenza), may be prescribed in some circumstances.

Painkillers can alleviate some of the symptoms, such as headache and body pains.

Some painkillers, such as aspirin, should not be given to children under 12.

Individuals with flu should:

  • stay at home
  • avoid contact with other people where possible
  • keep warm and rest
  • consume plenty of liquids
  • avoid alcohol
  • stop smoking
  • eat if possible

It is a good idea for people that live alone to tell a relative, friend, or neighbor that they have flu and make sure someone can check in on them.

When to see a doctor

A doctor only needs to be informed if:

  • the individual is frail or elderly
  • their temperature remains high after 4-5 days
  • symptoms worsen
  • the individual feels seriously ill
  • they become short of breath and/or develop chest pain

If worried, a phone call to the doctor may be a better solution than making an appointment.


In the majority of cases, flu is not serious - it is just unpleasant. For some people, however, there can be severe complications. This is more likely in very young children, in the elderly, and for individuals with other longstanding illness that can undermine their immune system.

The risk of experiencing severe flu complications is higher for certain people:

  • adults over 65
  • babies or young children
  • pregnant women
  • individuals with heart or cardiovascular disease
  • those with chest problems, such as asthma or bronchitis
  • individuals with kidney disease
  • people with diabetes
  • people taking steroids
  • individuals undergoing treatment for cancer
  • those with longstanding diseases that reduce immune system function

Some of the complications caused by influenza may include bacterial pneumonia, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Children may develop sinus problems and ear infections.


 Flu vaccination is the best protection against flu.

Over 200,000 people are hospitalized from flu complications each year, and about 36,000 people are estimated to die as a result of flu.

It is estimated that, globally, 250,000-500,000 people die each year as a result of flu.

In industrialized countries, the majority of deaths occur among people over the age of 65.

A flu epidemic - where a large number of people in one country are infected - can last several weeks. Health experts and government agencies throughout the world say that the single best way to protect oneself from catching flu is to get vaccinated every year.

There are two types of vaccinations, the flu shot and the nasal-spray flu vaccine. The flu shot is administered with a needle, usually in the arm - it is approved for anyone older than 6 months, including healthy people and those with chronic medical conditions.

The nasal-spray flu vaccine is a vaccine made with live, weakened flu viruses that do not cause illness.

Seasonal flu shot

A flu vaccine will contain three influenza viruses:

  • influenza (H3N2) virus
  • influenza (H1N2) virus
  • one B virus

As viruses adapt and change, so do those contained within the vaccines - what is included in them is based on international surveillance and scientists' calculations about which virus types and strains will circulate in a given year.

Protection begins about 2 weeks after receiving the vaccination.

Seasonal flu vaccinations should start in September or as soon as the vaccine is on hand, and continue throughout the flu season, into January, and beyond. This is because the timing and duration of influenza seasons are never the same. Flu outbreaks usually peak at around January, but they can happen as early as October.

Seasonal flu shots are not suitable for some people

Certain individuals should check with their doctor before deciding to have the flu vaccine, including:

  • Individuals with a severe allergy to chicken eggs.
  • Individuals who have had a severe reaction to a flu vaccination in the past.
  • Individuals who developed Guillain-Barré Syndrome within 6 weeks of receiving a flu vaccine.
  • Children under 6 months old.
  • Individuals experiencing a fever with a moderate-to-severe illness should wait until they recover before being vaccinated.


Three types of flu viruses exist - influenza A, influenza B, and influenza C. Types A and B viruses cause seasonal epidemics that hit the United States and Europe virtually every winter. The type C influenza virus causes mild respiratory illness and is not responsible for outbreaks.


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