ATLANTA — The Centers for Disease Control and Prevention's vaccine advisory panel voted to update its guidelines on antiviral treatment of influenza to include new information about antiviral resistance of seasonal influenza and to address influenza that is caused by the newly emergent pandemic strain of H1N1.
At the time of the meeting of the Advisory Committee on Immunization Practice, all pandemic H1N1 viruses tested were sensitive to oseltamivir and zanamivir and were resistant to the adamantadines. In contrast, seasonal H1N1 influenza is resistant to oseltamivir but susceptible to the other two antivirals.
Currently, all circulating seasonal influenza H3N2 and B strains are susceptible to zanamivir, Dr. Anthony J. Fiore of the CDC's Influenza Division said at the meeting.
Subsequent to the meeting, a patient with oseltamivir-resistant novel H1N1 was identified in Denmark. This development does not change the committee's recommendations, CDC spokesman Tom Skinner said in a interview.
Antiviral treatment should be started as soon as possible after illness onset.
Persons for whom antiviral treatment should be considered include those who have influenza viral pneumonia, or influenza and complicating bacterial pneumonia.
The treatment also should be considered for patients hospitalized with influenza and those at higher risk for influenza complications, regardless of illness severity.
Zanamivir is recommended if laboratory testing is not done or is negative but there is clinical suspicion of influenza.
The antiviral also is recommended if a patient tests positive for influenza A, both influenza A and B, or seasonal A (H1N1).
Combined treatment with oseltamivir plus rimantadine is an acceptable alternative if zanamivir is not available or can't be tolerated.
Either oseltamivir or zanamivir is recommended for positive A (H3N2) and novel A (H1N1) or B strains.
Rather than voting simultaneously on recommendations for chemoprophylaxis—as has been done previously with seasonal influenza—ACIP decided instead to include a short paragraph within the treatment guidelines about chemoprophylaxis that will include the address for the CDC's H1N1 Web page (www.cdc.gov/H1N1
The information on that site is updated frequently, and will likely be the most current information available. The recommendations on the need for chemoprophylaxis are expected to change as more becomes known about transmission of the novel H1N1 virus and vaccine availability, ACIP member Dr. Kathleen Neuzil said in an interview. Dr. Neuzil is an associate professor of medicine in the Division of Allergy and Infectious Diseases at the University of Washington, Seattle.
Currently, all strains of influenza are susceptible to zanamivir, Dr. Anthony J. Fiore said.
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