This type of influenza is the most common and is associated with the most severe symptoms. The medications are not effective against other strains of influenza. In an average year, more than 100,000 Americans are hospitalized with influenza and more than 20,000 die.
Travel is a significant risk factor for acquiring influenza.
The travel industry is working closely with public health authorities to limit influenza transmission to travelers. For example, many cruise lines have initiated surveillance for respiratory illness among passengers and crew and are vaccinating their crew against influenza. Being in close quarters aboard ship over an extended period favors transmission of infectious diseases. If that year's match is not good, the vaccine is less effective. The incubation period for influenza is 1 to 4 days.