Oct 14, 2008 (CIDRAP News) In a sign that influenza season is approaching, the US Centers for Disease Control and Prevention (CDC) recently reported that a handful of states have seen sporadic flu cases and that the earliest signs suggest that this year's vaccine is a good match for circulating strains.
For the week that ended Oct 4, the CDC said in an Oct 10 update that seven states reported sporadic seasonal influenza activity: California, Connecticut, Florida, Hawaii, Idaho, New York, and Wyoming. Forty-one other states reported no activity, and twoMontana and Washingtondid not report.
Over the summer months (May 18 through Sep 27), the CDC antigenically characterized a small number of influenza isolates, the report said. Of the six isolates, four were type A/H1, one was type A/H3, and one was type B. "All six viruses are antigenically similar to the components selected for the 2008-2009 influenza vaccine," the CDC said. For the H1 component the vaccine strain is similar to A/Brisbane/59/2007, for the H3 component, A/Brisbane/10/2007, and for the B component, B/Florida/4/2006.
Reports from US labs affiliated with the World Health Organization and the National Respiratory and Enteric Virus Surveillance System say that of 40 influenza viruses identified during September, 1 (2.5%) was an H1 virus, 4 (10%) were H3 viruses, 29 (72.5%) were nonsubtyped A viruses, and 6 (15%) were B viruses.
Last year a number of countries, including the United States, reported increased resistance of H1N1 viruses to the antiviral drug oseltamivir (Tamiflu). The CDC said that since May 18 it has tested 10 isolates for antiviral resistance. It found that 2 of 6 H1N1 viruses showed resistance to oseltamivir, but no resistance was found in H3N2 and B viruses. All retained sensitivity to zanamivir (Relenza), the other neuraminidase inhibitor.
Of six type A viruses tested for resistance to the older flu drugs known as adamantanes, two were positive: one H3N2 virus and one of five H1N1 viruses.
"Based on the level of oseltamivir resistance in only one influenza subtype, H1N1, and the persisting high levels of resistance to the adamantanes in H3N2 viruses, CDC continues to recommend the use of oseltamivir and zanamivir for the treatment or prevention of influenza," the report said. "Use of amantadine or rimantadine is not recommended."
CDC's week 40 influenza report