According to the Centers for Disease Control and Prevention, respiratory influenza viruses are highly contagious due to the ease with which they are transmitted from one person to another, often before the infected person develops symptoms. Seasonal respiratory influenza illnesses, generally categorized as type A viruses, traditionally appear in fall and winter months. Some exposures do not develop into actual illness but many do, especially to those in higher risk groups. The timing of vulnerability to exposure is referred to as the period of communicability, while the timing from infection to the development of the disease is referred to as the incubation period.
Mode of Transmission
The mode of transmission for respiratory influenza viruses is from droplets propelled in the air by coughing, sneezing or talking. The cycle of transmission begins once the droplets carrying the infectious influenza virus are expelled into the air where they are either inhaled or picked up on the hands, skin or clothing after touching contaminants on environmental surfaces.
Period of Communicability
Medline, The U.S. Library of Medicine, defines communicability as the time it takes an infectious agent to be transmitted from an infected person to another person. Once infected with influenza type illnesses, the affected person may begin shedding the virus to others one day before signs and symptoms occur and continue to be contagious 5 to 7 days after symptoms begin. This makes prevention all but impossible at this stage of the disease. Modifiers include age and the general health of the infected person.
Incubation Period
The incubation period is the time it takes for a person who has been exposed to the virus to become infected. The Merck Manual's Online Medical Library section on Influenza reports the incubation period may be from 1 to 4 days, averaging about 48 hours from exposure.
Preventing Communicability
All major national professional organizations recommend influenza vaccination to prevent the spread of seasonal and H1N1 influenzas from one person to another. The Advisory Committee on Immunization Practices makes recommendations to the Centers for Disease Control and Prevention. In February of 2010, they recommended a universal annual influenza vaccine be made available to all people 6 months and older for the 2010 and 2011 seasonal flu program.The vaccine will include the 2009 H1N1 strain. Universal vaccination is the most effective method of preventing the spread of contagious influenza strains from one person to the other.
