While vigilant hand washing and receiving the flu shot are helpful in preventing the flu, no measure is 100 percent effective. According to the Centers for Disease Control and Prevention, the flu is very contagious and can even go on to cause other complications like pneumonia, ear infections and dehydration. Understanding the flu incubation period is a helpful tool for preventing the spread of the virus. The incubation period refers to the time between when you are exposed to the flu virus and when you first experience symptoms.
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Influenza Incubation Period
The average incubation period for the flu is 2 days, but it can last anywhere from 1 to 4 days in healthy adults. Peak viral excretion, or the time when infected individuals are most contagious, is in the first 24 to 48 hours of symptoms. Once an infected person becomes symptomatic, those who also become infected with the flu will develop symptoms within 2 to 4 days. A March 2011 study in "The Journal of Theoretical Biology" found that average flu incubation periods in a small aircraft and bus were 1.48 and 2.05 days, respectively, suggesting that incubation periods may be shortened when individuals are confined to close quarters.
The flu virus is present in the respiratory secretions of infected individuals. When a person coughs or sneezes, large droplets containing the virus are released into the air, putting those in close proximity at risk of infection. The flu virus can also survive on hard surfaces for up to 48 hours, so it may also be transmitted via hand contact. Regardless of how someone is exposed to the flu, the average incubation period is 1 to 4 days.
Peak Infectiveness Is Early
While it may be possible to transmit the flu virus before symptoms occur, a March 2009 study in "Public Health Reports" found that the most likely time is the first 2 days of symptoms, and it is unclear how infectious adults are before symptoms occur. Because of this short time frame and high infectiousness early in the illness, the flu virus can spread rapidly though communities.
Infectivity and Special Populations
Like adults, children’s peak infectivity occurs within the first 2 days of symptoms, but they are actually often contagious before symptoms begin as well. The January 2006 study in “Emerging Infectious Diseases” stated that children begin viral shedding days before symptoms occur and last up to 21 days. A November 2008 study in the “Journal of Infectious Diseases” reported that individuals with chronic illness and immunocompromised individuals, such as those with cancer, were considered contagious for over 2 weeks.
Antivirals and Incubation Period
Your healthcare provider may recommend an antiviral medication once you are diagnosed with the flu. These medications slow the growth of the flu virus and can rapidly improve symptoms. The “Current Practice Guidelines in Primary Care” recommends starting antiviral therapy within 48 hours of experiencing flu symptoms. However, even though these medications improve symptoms, the flu virus is still present in the bodily secretions and thus can still transmitted to others.
- Emerging Infectious Diseases: Nonpharmaceutical Interventions for Pandemic Influenza, International Measures
- Journal of Infectious Diseases: Prolonged Influenza Virus Infection During Lymphocytopenia and Frequent Detection of Drug-Resistant Viruses
- Journal of Infection and Chemotherapy: Spread of Viral Infection to Family Members From Influenza Patients Treated With a Neuraminidase Inhibitor
- Current Practice Guidelines in Primary Care 2014
- Journal of Theoretical Biology: Estimation of the Incubation Period of Influenza A (H1N1-2009) Among Imported Cases: Addressing Censoring Using Outbreak Data at the Origin of Importation
- Centers for Disease Control and Prevention: Key Facts About Influenza
- Public Health Reports: Does Influenza Transmission Occur From Asymptomatic Infection or Prior to Symptom Onset?