Girl receiving shot at doctor's office

Flu Facts

What you should know about influenza
Author: Sarah Aldridge

In the middle of winter, it’s important to know the truth about influenza, the virus that causes the flu.

Influenza Virus, More Than a Nasty Cold

Influenza, or the “flu,” is caused by viruses that infect the upper respiratory tract. It is spread when an infected person coughs or sneezes, spraying droplets into the air. Adults are contagious one day before symptoms appear and up to a week afterward. Children can spread the virus even longer. Symptoms typically begin one to four days after influenza enters the body.

Vaccination for All

Open box of tissuesThe Centers for Disease Control and Prevention (CDC) encourages everyone over the age of 6 months to get vaccinated yearly. The influenza vaccine is composed of the three most common strains of influenza predicted to strike during the next flu season. That’s why you need to be vaccinated yearly. Even though flu vaccines are typically given in the fall, you can be vaccinated now. Once you’ve been vaccinated, it takes about two weeks for your body to create antibodies to influenza.

You cannot get the flu from the vaccine, but it is possible to get a milder version of it.

Vaccine Caution

Because of the risk of bruising and of developing a muscle bleed, vaccines should not be delivered intramuscularly in people with bleeding disorders. Instead, intradermal or subcutaneous routes are preferred. If you haven’t been vaccinated against influenza this year, there’s still time. Fighting the flu only takes one person—you.

Flu vs. Cold Symptoms

Here’s a handy chart to help you differentiate between cold and flu symptoms:
Symptoms Cold Influenza
Cough Often, mild to deep Common, can be severe
Extreme exhaustion Never Usual, at the beginning
Fatigue, weakness Sometimes Common, up to 2 weeks
Fever Rare Usual, 100°–102°, 3–4 days
Headache Rare Common
Muscle aches Mild Usual, severe
Congestion, sneezing Often Sometimes
Adapted from “Is It a Cold or the Flu?”
National Institute of Allergy and Infectious Diseases,