Table of ContentsView AllTable of ContentsBefore SymptomsAfter SymptomsHow Flu SpreadsIf You’re SickPreventionNext in Flu GuideInfluenza Treatments: How to Get Better at Home or With Medication
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Table of Contents
Before Symptoms
After Symptoms
How Flu Spreads
If You’re Sick
Prevention
Next in Flu Guide
The period of time between exposure to theinfluenza (flu) virusand the appearance ofsymptoms—called theincubation period—is around two days. Even so, you can pass the virus to others 24 hours before symptoms begin and for five to seven days after symptoms develop.
This is why it is important to stay home from work or school if you have the flu and to take standard precautions (like washing your hands and covering your mouth while coughing or sneezing) to avoid infecting others.
This article explains how long the flu is contagious, the ways in which it is spread, and what to do if you’ve been exposed. It also explains how to protect others from influenza if you have it.
Verywell / Joshua Seong
Contagiousness Before Flu Symptoms
The incubation period for the flu is between one and four days, with an average of two days according to the Centers for Disease Control and Prevention (CDC).This means that if you are exposed to the virus and infected, you will start to experience symptoms (such as fever andbody aches) anywhere from 24 hours to four days after exposure.
Once infected, you can be contagious for up to 24 hours prior to the appearance of symptoms. During thisasymptomatic(symptom-free) period, you can infect others directly or indirectly without even knowing it.
Risk of Asymptomatic TransmissionIn 2021,researchers in South Africa aimed to establish the rate of asymptomatic flu transmission among 1,116 participants in 225 urban and rural households.The study found that individuals with asymptomatic flu transmitted infection to 29 (6%) of 509 household contacts—meaning that roughly one of every 16 infections was passed from someone with no flu symptoms.
Risk of Asymptomatic Transmission
In 2021,researchers in South Africa aimed to establish the rate of asymptomatic flu transmission among 1,116 participants in 225 urban and rural households.The study found that individuals with asymptomatic flu transmitted infection to 29 (6%) of 509 household contacts—meaning that roughly one of every 16 infections was passed from someone with no flu symptoms.
In 2021,researchers in South Africa aimed to establish the rate of asymptomatic flu transmission among 1,116 participants in 225 urban and rural households.
The study found that individuals with asymptomatic flu transmitted infection to 29 (6%) of 509 household contacts—meaning that roughly one of every 16 infections was passed from someone with no flu symptoms.
Contagiousness After Flu Symptoms
Once flu symptoms start, adults can pass the virus to others for around seven days. According to the CDC, the virus is most contagious on the third or fourth day.After that, the contagiousness rapidly declines as theimmune systemgains control over the virus.
In children, the flu can sometimes be contagious for more than seven days.This is because children have less mature immune systems and can take longer to control the virus. The same may apply to older adults and people withcompromised immune systems.
As a general rule, the presence of symptoms is a good way to tell if you are still contagious. Until symptoms clear, it is best to consider yourself contagious and take steps to avoid infecting others.
How Does the Flu Spread?
Influenza is a respiratory infection that is mainly spread throughrespiratory droplets. These are tiny secretions from the mouth or nose that get airborne whenever you cough, sneeze, laugh, or even talk. Once airborne, the virus-filled droplets can travel as far as 6 feet and enter the mouth or nose of someone else.
How Long Does Flu Live Outside the Body?Research suggests that flu viruses can remain infectious outside of the body for several hours, They tend to survive longer on hard surfaces like stainless steel or plastic than on soft, porous surfaces like fabric.
How Long Does Flu Live Outside the Body?
Research suggests that flu viruses can remain infectious outside of the body for several hours, They tend to survive longer on hard surfaces like stainless steel or plastic than on soft, porous surfaces like fabric.
During the cold winter months, the flu spreads rapidly. Contrary to popular belief, it isnot due to cold weather. Cold temperatures simply allow the virus to survive longer. Winter winds can also transport the droplets far longer than six feet.
What to Do if You’re Sick With Flu
If you have the flu, you should stay home at least 24 hours after your fever has gone without the use of fever-reducing medicines likeTylenol (acetaminophen).
If you don’t have a fever but still have symptoms, wait until your symptoms improve and it has been at least four to five days since the start of your illness.
You get over the flu faster with the following steps:
Warning to ParentsNever give aspirin to children or teens with fever as it can cause a potentially deadly reaction calledReye’s syndrome.Children under 4 years should not be given cough or cold medicines as they can cause serious and potentially life-threatening side effects.
Warning to Parents
Never give aspirin to children or teens with fever as it can cause a potentially deadly reaction calledReye’s syndrome.Children under 4 years should not be given cough or cold medicines as they can cause serious and potentially life-threatening side effects.
Preventing Flu in Others
Flu is something that most people get at one time or another. If it happens, you need to take care of yourself while reducing the risk of infection in others.
The CDC recommends the following:
Flu VaccinationThe best way to avoid passing the flu is to avoid getting it in the first place. The annualflu vaccineis recommended for everyone over 6 months of age, ideally in September or October, to ensure better protection throughout theflu season.
Flu Vaccination
The best way to avoid passing the flu is to avoid getting it in the first place. The annualflu vaccineis recommended for everyone over 6 months of age, ideally in September or October, to ensure better protection throughout theflu season.
How Effective Is the Flu Vaccine?
Summary
Once exposed to the influenza virus, it can take anywhere from one to four days for symptoms to appear and five to seven days more for symptoms to clear. You can be contagious up to 24 hours before symptoms stop and continue to be contagious until your symptoms improve and you no longer have a fever. Peak contagiousness occurs on day three or four of your illness.
A Word From Verywell
—STEFFINI STALOS, DO, MEDICAL EXPERT BOARD
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Centers for Disease Control and Prevention.How flu spreads.
Centers for Disease Control and Prevention.Key facts about influenza (flu).
Cohen C, Kleynhans J, Moyes J, et al.Asymptomatic transmission and high community burden of seasonal influenza in an urban and a rural community in South Africa, 2017-18 (PHIRST): a population cohort study.Lancet Glob Health.2021 Jun;9(6):e863-74. doi:10.1016/S2214-109X(21)00141-8
Centers for Disease Control and Prevention.Stay home when you are sick.
Centers for Disease Control and Prevention.Flu treatment.
National Organization for Rare Disorders.Reye syndrome.
U.S. Food and Drug Administration.Should you give your kids medicine for cough and colds?
Centers for Disease Control and Prevention.Healthy habits to help protect against flu.
Centers for Disease Control and Prevention.Seasonal flu vaccines.
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