The flu is contagious. People who catch the flu can transmit the virus to another person even before symptoms appear.

A person can still be contagious up to 1 week after their symptoms appear. Some people may continue to transmit the virus even after 7 days.

Keep reading to learn more about how the flu spreads and how people can limit its transmission. We also discuss treatment options and when to see a doctor.

a woman coughing in public because of the flu which could spread to others as it is contagiousShare on Pinterest
A person may transmit the flu virus through droplets when they sneeze.

The flu is a contagious infection of the respiratory tract.

Most experts agree that influenza viruses spread mainly through droplets. People produce droplets when they cough, sneeze, breathe, or talk. These droplets, which may contain the virus, can deposit on the upper or lower respiratory tract of another person.

Respiratory droplets from sneezing, coughing, breathing, or talking are larger than 5 micrometers. These droplets cannot remain suspended in the air, but if their propulsion has enough momentum, they can reach another person. People who have the flu can spread it to others who are up to 6 feet away.

Droplets can also deposit on surfaces or objects, or transmission can occur through direct person-to-person contact. Although it is less common for people to catch the flu from touching a contaminated surface and then touching their face, doctors recommend hand washing and disinfecting surfaces often during the flu season.

People who catch the flu are most contagious in the first 3–4 days after symptoms begin. Most people become contagious 1 day before symptoms appear. Therefore, they can transmit the virus to another person even before they know that they are unwell.

Other people may carry the virus but not present any symptoms. These asymptomatic individuals can still transmit the virus to another person who may become sick.

People who are generally in good health when they get the flu may be able to infect another person up to 1 week after becoming sick. Young children and people with weakened immune systems may be able to infect others with the flu virus for longer than 7 days.

Once a person catches the flu, they may experience the following symptoms:

Not everyone who has the flu will develop a fever.

These symptoms may resemble those of the common cold. Flu symptoms will usually begin rapidly after infection, whereas cold symptoms tend to have a more gradual onset.

Most people recover from the flu within a few days to less than 2 weeks, but it can sometimes last longer. Some people may develop complications from the flu, such as pneumonia, which can be life threatening. Sinus and ear infections may also occur following the flu, but these are less severe complications.

People most at risk of developing complications following the flu include:

  • young children
  • immunocompromised individuals
  • pregnant women
  • older adults

Complications from the flu may develop in as little as 2 days from the beginning of flu symptoms. Flu viruses begin replicating in the upper and lower respiratory tract at the time the pathogen deposits, and they peak, on average, about 48 hours later.

For most people, the flu causes mild symptoms. Mild symptoms do not require treatment. People who are not in an at-risk population and do not have other chronic diseases may not require antiviral treatment.

Doctors can prescribe antiviral medications to treat or prevent the flu during outbreaks in hospitals or long-term care facilities.

Antiviral drugs to treat the flu resulting from the influenza A and B viruses include:

  • oseltamivir (Tamiflu)
  • zanamivir (Relenza)
  • peramivir (Rapivab)

Doctors can prescribe oseltamivir to people aged 1 year and older to prevent the flu in those belonging to high risk groups in outbreak situations.

Amantadine (Symmetrel) and rimantadine (Flumadine) are two antivirals effective against only influenza A. However, in recent years, influenza A has developed a resistance to these two drugs.

Researchers have seen low resistance rates of influenza A and B against oseltamivir, zanamivir, and peramivir. Still, the flu virus can mutate and develop resistance at any time. Following treatment, people with a weakened immune system are at higher risk of the virus developing resistance.

The best treatment for the flu is prevention. Flu viruses are detectable all year round in the United States, but the transmission of the virus ramps up in the fall and winter. The timing of the flu season changes every year, but it generally starts in October and can last until May. The peak of the season occurs between December and February.

All year round, but particularly during the flu season, people should:

  • stay home if they are ill
  • avoid contact with others who are sick
  • cover their nose and mouth when sneezing
  • wash their hands often
  • avoid touching their face, eyes, mouth, and nose
  • clean and disinfect surfaces and objects with a cleaner that kills viruses that cause the flu

The Centers for Disease Control and Prevention (CDC) state that by practicing everyday preventive actions, people and communities can help slow down the spread of the flu.

The best way to prevent the flu is to get the flu vaccine every year. Experts recommend vaccination for everyone aged 6 months and older, with people over 65 years of age receiving high dose vaccination.

The vaccine contains some egg protein, but it is safe for people with an egg allergy who only develop hives.

Healthy people who catch the flu do not usually need medical attention unless they develop complications.

Medical attention is necessary for people in high risk populations, such as young children, adults over 65 years of age, and people with certain chronic health conditions.

Anyone who feels very ill or worried about their flu symptoms should speak with a doctor. The following table lists the emergency warning signs that indicate that a person should seek medical care.

Rapid breathing or trouble breathing Shortness of breath or difficulty breathing
Blue color to the lips or face Persistent pain or pressure in the chest or abdomen
Chest pain Dizziness, confusion, inability to stimulate
Ribs pulling in with each breath Seizures
Severe muscle pain Not urinating
Not urinating, dry mouth, no tears when crying Severe weakness or unsteadiness
Not alert or interacting with others Severe muscle pain
Seizures Fever or cough that improves but then returns or worsens
Fever above 104°FWorsening of chronic conditions
Any fever in children less than 12 weeks old
Fever or cough that improves but then returns or worsens
Worsening of chronic conditions

Some people may not know whether they have the flu or another infection because the symptoms of the flu are similar to those of other respiratory infections.

If a doctor needs to know whether a person has the flu, they will order a laboratory test that detects parts of the virus in nasal or throat secretions.

A doctor may not always order a test to detect the flu virus in people with flu symptoms. The results of the test do not necessarily influence how the doctor will treat the person. With mild symptoms, doctors recommend that people stay home to prevent the spread of the flu.

People at risk of complications from the flu should consult with a doctor to monitor the progression of the infection closely. These individuals are more likely to require hospitalization and have a higher risk of complications. In some cases, the flu can even be fatal.

The flu is contagious from the day before symptoms begin, which means that people can transmit the flu virus to another person before they notice that they are unwell.

An otherwise healthy person remains contagious until about a week after the appearance of symptoms. Others may continue to spread the flu after 7 days.

To limit the spread of the flu, doctors recommend annual flu shots, frequent hand washing, and cleaning of frequently touched surfaces at home, school, and work.