Lisa Grohskopf, MD, MPH Medical Officer Influenza Division Centers for Disease Control and Prevention U.S. Influenza Surveillance National Center for Immunization & Respiratory Diseases Influenza Division VRBPAC Meeting February 25, 2011

Characteristics of Recent Influenza Viruses Tested at CDC Of 644 U.S. viruses antigenically characterized at CDC since October 1, 2010:  85 (13%) Influenza A (H1N1)  85 (100%) A/California/7/2009-like  348 (54%) Influenza A (H3N2)  345 (99%) A/Perth/16/2009-like  211 (33%) Influenza B  199 (94%) Victoria lineage; 198 (99%) B/Brisbane/60/2008-like  12 (6%) Yamagata lineage High level resistance to adamantanes persists among Influenza A isolates; A(H1N1), A(H3N2) and B virus isolates tested remain susceptible to neuraminidase inhibitors

Percentage of Visits for Influenza-like Illness (ILI) Reported by the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), Weekly National Summary, September 30, 2007 – February 12, 2011

Influenza Positive Tests Reported to CDC by U.S. WHO/NREVSS Collaborating Laboratories, National Summary, Percent Positive Number of Positive Specimens

Epidemic Threshold Seasonal Baseline Pneumonia and Influenza Mortality for 122 U.S. Cities Week Ending 02/12/

Number of Deaths Reported = Number of Deaths Reported = Number of Deaths Reported = 282 Deaths Reported Current WeekDeaths Reported Previous Week Number of Deaths Reported = 35 Number of Influenza-Associated Pediatric Deaths by Week of Death: season to present

Key Points  Influenza A(H3N2), A(H1N1), and B strains continue to co-circulate in the U.S.  Recently characterized strains appear to be well- matched to the recommended seasonal vaccine  Recently circulating viruses remain susceptible to neuraminidase inhibitors  In the U.S., influenza activity remains high in recent weeks  Increase in proportion of influenza A viruses identified as A(H1N1) since the beginning of the U.S. season