I assume that flu season occurs in the Southern Hemisphere during its winter months. With so many people traveling the world, shouldn’t the flu vaccine be offered twice annually?
—Elizabeth M. Chang, MD, East Palatka, Fla.

You are correct about the Southern Hemisphere’s antipodal seasonal variation. Importantly, the influenza virus has no seasonal variation within the tropical regions closer to the Equator so that any of your patients planning exotic trips should be offered a flu vaccine prior to departure, no matter what the time of year. Despite globalization from increasing air travel, influenza is still a seasonal illness in the United States, and annual vaccination is recommended by the CDC in the late autumn for maximum benefit. Pursuing the annual vaccination strategy has resulted in close to 65% coverage of those older than 65 years of age in this country.
—Cedric W. Spak, MD, MPH (113-11)