Influenza activity locally and nationally is at a low level, which is typical for this time of year. Flu season typically peaks in January or later and has been in February or March in 11 of the past 20 seasons.

Most influenza viruses identified and characterized this season are well-matched to the current vaccine. However, it is too early to determine which influenza virus type or subtype will predominate this season. Vaccination efforts should continue during December and throughout the influenza season, which can persist into spring.

Since Sept. 28, 68 influenza viruses from 15 states have been tested for antiviral resistance by CDC. Preliminary data show that 45 of the 46 influenza A (H1N1) viruses tested were resistant to oseltamivir (the majority of specimens were from two states). All oseltamivir-resistant A (H1N1) viruses have been sensitive to zanamivir, and most have been susceptible to the adamantanes. All seven influenza A (H3N2) and 15 influenza B viruses tested were sensitive to oseltamivir and zanamivir. All tested influenza A (H3N2), and influenza B viruses have also been sensitive to zanamivir. Most influenza A (H3N2) viruses worldwide are resistant to adamantanes; adamantanes are not effective against influenza B infections.

At this time, too few specimens from a limited geographic area have been tested to estimate the prevalence of oseltamivir resistance for the 2008–09 season. Alternatives for antiviral treatment in the setting of widely circulating oseltamivir-resistant viruses might include preferential use of zanamivir or therapy with a combination of antivirals for certain patients, please see the 2008 Advisory Committee on Immunization Practices (ACIP) influenza recommendations.

Currently, the neuraminidase inhibitors oseltamivir and zanamivir remain the recommended medications for treatment and chemoprophylaxis of influenza. Please remain alert for changes in recommendations that might occur as the influenza season progresses is if surveillance data indicate a substantial and widespread increase in the prevalence of oseltamivir-resistant influenza viruses.

Additional information regarding influenza including local influenza surveillance and influenza vaccine.

Influenza information from CDC is available at www.cdc.gov/flu.

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