Influenza ("Flu")

Colds and flu are both extremely common infections.  However, colds are hundreds of times more common than influenza except during flu epidemics.  These illnesses share many features: both are caused by viruses, are highly contagious, involve the respiratory tract, and have a fairly predictable seasonal pattern. Because of these similarities, the terms “cold” and “flu” are often used interchangeably.  However, there are important differences between these two types of infections, particularly in terms of prevention, severity and treatment.

What, exactly, is the Flu?

The flu is an infection of the respiratory tract caused by the influenza virus.  There are three types of this virus, labeled types A, B, and C.  The yearly spread of the influenza virus typically occurs during the winter months and may be associated with flu epidemics.  The proteins that coat the flu virus change constantly.  As a result, our immune systems do not recognize—and therefore cannot protect us from—new strains.  These new strains circulate around the world every few years, causing frequent, widespread epidemics.  This shifting nature of the virus, plus the danger of life-threatening complications from the infection, combine to make the flu a major public health threat. The life-threatening complications mainly occur in the elderly, the debilitated and the very young.

How does one catch the Flu?

Unlike colds, which are most likely spread by direct contact, the influenza virus is mainly spread by airborne transmission.  When a person who has the flu sneezes, coughs, or even speaks, he or she fills the air with microscopic droplets that are filled with flu particles.  These droplets are so small that they remain suspended in the air long enough to be inhaled by another person.  Once the virus lands on the lining of the nose, throat, or airways, it invades the cells in its new host and starts reproducing itself rapidly.


A mild case of the flu may seem very much like a common cold.  More often, the flu is associated with the sudden onset of headache, fever, chills, muscle aches, malaise ( an overall lousy feeling), cough and sore throat.  These symptoms typically begin in such an abrupt  fashion that people can recall the exact time that they got sick.


Since the late 1940s, the flu vaccine has been the best way to prevent influenza or lessen its severity.  Because the virus undergoes constant change, new vaccines are developed yearly to protect the public from the most recently isolated viral strains.

Like most vaccines, the flu vaccine is given as an injection, or shot.  For maximal protection for the duration of the flu season, the best time to receive the vaccine is from early October to mid-November.  However, the vaccine can be given to children and adults at any point during the flu season, even after the influenza virus has begun to spread in the community.

Is it a Cold or the Flu?

Signs and Symptoms Influenza Colds
Onset Suddne (within a few hours) Gradual (over a day or two)
Fever Characteristic, high (over 101F); lasting 2-4 days Occasional
Cough Nonproductive; can become severe Hacking at first, later may be productive
Headache Prominent and often severe Frequent and usually less severe
Myalgia Usual; lften severe Slight
Fatigue; weakness Can last up to 2-3 weeks Very mild
Exptreme exhaustion Early and prominent Seldom
Chest discomfort Common Mild to moderate
Stuffy, runny nose Occasional Very common
Sneezing Occasional Usual
Season Most cases between Nov-Feb All year round with peak in the winter
Severity Severe illness, especially in first 2-4 days Mild to moderate illness


The treatment of “the flu” without complications is aimed at the most prominent symptoms at the time.
(Please see “Antibiotics” for more information regarding why they are not used for uncomplicated colds/flu.)


Headaches, minor aches and pains, fever Analgesics—
  Tylenol, Bayer, Anacin,  Motrin IB, Advil
Nasal congestion, sinus pressure and sinus congestion Decongestants—
  Sudafed, Privine, Afrin, Neo-Synephrine
Runny nose, watery eyes Antihistamines (May cause drowsiness)
  Dimetapp Chlor-Trimeton, Tavist-1, Benadryl
Cough Cough Suppressants—
  Robitussin DM
Cough Expectorants—
  Robitussin (various preparations)
Sore throat Local Anesthetics—
  Cepacol, Sucrets, Cepastat Lozenges

If your physician diagnoses “the flu” early enough in its course, other medicines may be prescribed.


The most serious complication of influenza is pneumonia—an infection of the lungs.  Pneumonia can be caused by the influenza virus itself, or by bacteria that are able to enter the lungs because natural defenses have been weakened by the flu.  Anyone with persistent symptoms beyond a week merits medical attention.  In addition, marked difficulty breathing or chest pain associated with coughing at any point during the illness should prompt a visit to the doctor.


Guidelines for the prevention and treatment of Influenza and The Common Cold, American Lung Association, August 2008