How the flu spreads and treatments that work: 5 Fast Facts

Influenza, which is more commonly known as the flu, is a highly contagious respiratory illness caused by viruses.

There are three types of influenza viruses that make people sick: A, B and C. Influenza A and B are the viruses that cause the most severe illness and lead to widespread outbreaks, the Cleveland Clinic says.

As flu activity nears its typical peak, people online are asking questions about how the virus spreads and ways to treat it. 

Here are five VERIFIED facts about flu transmission, including the typical incubation period and length of time a person is contagious, and treatments. 

THE SOURCES

• The Centers for Disease Control and Prevention (CDC)
• The World Health Organization (WHO)
• Johns Hopkins Medicine 
• The Mayo Clinic
• New York Department of Health
• The American Lung Association
• UCLA Health
• Sandra Campbell, pharmacist and Michigan State University Health Care Pharmacy director

WHAT WE FOUND

1. The flu can spread through the air and surfaces. 

Flu viruses spread easily, with “rapid transmission in crowded areas” such as schools and nursing homes, the World Health Organization (WHO) says.

According to the Centers for Disease Control and Prevention (CDC), flu viruses mainly spread through the air in droplets when an infected person coughs, sneezes or talks.

People can also get the flu from touching surfaces or objects that have the virus on them, and then touching their own mouth, nose or eyes. But this happens less often than spread through droplets in the air, the CDC says. 

2. People can spread the flu to others even before having symptoms.

Most people can pass the flu to others beginning about one day before symptoms start, according to the New York Department of Health and Johns Hopkins Medicine.

The CDC says people with the flu are most contagious in the first three to four days of their illness.

A person with the flu remains contagious up to a week after getting sick, though some people with weakened immune systems can infect other people for several weeks, the CDC and Johns Hopkins Medicine say. 

3. Flu symptoms usually begin about 2 days after exposure to the virus. 

The time from flu infection to illness, which is known as the incubation period, ranges from about one to four days, according to the CDC and WHO.

But flu symptoms typically begin about two days after a person is infected by someone who has the virus, the health agencies say. 

Unlike cold symptoms that come on gradually, “the onset of influenza is very sudden,” pharmacist and Michigan State University Health Care Pharmacy director Sandra Campbell says.

Common flu symptoms include a fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue. Some people may have vomiting and diarrhea, but this is more common in children than adults, the CDC says. 

4. There are antiviral medications that can treat the flu.

People with the flu often need only rest and liquids to recover. They can also take over-the-counter pain relievers such as acetaminophen and ibuprofen to combat fever, headache and body aches. 

RELATED: Yes, soup can make you feel better when you're sick

But those with a severe infection or who are at higher risk of complications from the flu may receive a prescription for an antiviral medicine. People who are 65 and older, adults with certain chronic health conditions such as asthma, heart disease, diabetes and chronic kidney disease, and pregnant people are at higher risk of flu complications. 

Common antiviral medications used to treat the flu include oseltamivir (Tamiflu), baloxavir (Xofluza) and zanamivir (Relenza). These prescription drugs work best when they are started early, such as one to two days after flu symptoms begin, the CDC says. 

Antiviral drugs can lessen your symptoms and shorten the time a person is sick by one to two days, according to the CDC. They may also prevent some flu complications such as pneumonia. 

A person should visit the emergency room when the flu is severe enough to keep them from normal functions, such as breathing comfortably, thinking clearly, eating, drinking and getting to the bathroom, UCLA Health says. 

RELATED: No, liquid medication is not more effective than capsules

5. The flu shot is the best way to prevent the flu, but it isn’t immediately effective. 

The best way to reduce the risk of the flu is getting vaccinated every year, the American Lung Association and CDC say.

But the flu shot isn’t immediately effective. It takes about two weeks for the body to build up immunity to the flu after receiving the vaccine, according to the American Lung Association and Mayo Clinic. 

Other good health habits, such as washing your hands often, keeping your distance when you or someone around you is sick, and covering your mouth and nose with a tissue or elbow when you cough or sneeze, can also prevent the flu from spreading, the American Lung Association says.  

This story is also available in Spanish / Lee este artículo también en español: Cómo se transmite la gripe y los tratamientos efectivos: 5 datos breves