Today's CDC media update raised issues for all three seasonal flu serotypes. 93% of influenza B isolates was B/Yamagata/26/88, which doesn't match the vaccine strain (B/Victoria02/87). 87% of the H3N2 was A/Brisbane/10/2007, which doesn't match the vaccine strain (A/Wisconsin/67/2005). H1N1 did match the vaccine strain (Solomon Island/3/2006), but 8.1% was Tamiflu resistant in the United States. Moreover the incidence of flu positives was above the epidemic threshold for the four week in a row. Last week it rose dramatically above the threshold.

The increase in Tamiflu resistance paralleled increases elsewhere, including Europe. The cause of the increase does not appear to be treatment of human seasonal flu with oseltamivir (Tamiflu), because the first 71 cases tested in Japan were negative for the resistance H294Y.

The timing of the rise is curious, since Tamiflu treatment for seasonal flu has not risen, and no cases have been identified in Japan, where oseltamivir use is highest.

However, the rise does follow increased use of Tamiflu blankets to treat H5N1, and H274Y is the dominant change in H5N1 treated patients.