This year's flu season: 'moderately severe'.

• Position: H3N2 Viruses

Getting a flu vaccine this season reduces a person's risk of having to go to the doctor because of flu by 23% among individuals of all ages, according to the Centers for Disease Control and Prevention, Atlanta, Ga.

Since the CDC began conducting annual flu vaccine effectiveness (VE) studies in 2004-05, overall estimates for each season have ranged from 10% to 60% effectiveness in preventing medical visits associated with seasonal influenza illness. The report says this season's vaccine offers reduced protection, and this underscores the need for additional prevention and treatment efforts, including the appropriate use of influenza antiviral medications for treatment.

"Physicians should be aware that all hospitalized patients and all out patients at high risk for serious complications should be treated as soon as possible with one of three available influenza antiviral medications if influenza is suspected, regardless of a patient's vaccination status and without waiting for confirmatory testing," stresses Joe Bresee, branch chief in CDC's Influenza Division. "Health care providers should advise patients at high risk to call promptly if they get symptoms of influenza."

One factor that determines how well a flu vaccine works is the similarity between the flu viruses used in vaccine production and the flu viruses actually circulating. During seasons when vaccine viruses and circulating influenza viruses are well matched, VE between 50% and 60% has been observed.

H3N2 viruses have been...