Lisa Grohskopf, MD, MPHMedical Officer

Influenza DivisionCenters for Disease Control and Prevention

U.S. Influenza Surveillance

National Center for Immunization & Respiratory Diseases

Influenza Division

VRBPAC MeetingFebruary 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, 2010-11

Per

cent

Pos

itive

Num

ber

of P

ositi

ve S

peci

men

s

Epidemic Threshold

Seasonal Baseline

Pneumonia and Influenza Mortalityfor 122 U.S. CitiesWeek Ending 02/12/2011

2007 20082006 2009 2010 2011

0

5

10

15

20

25

30

35

402

00

7-4

0

20

07

-46

20

07

-52

20

08

-06

20

08

-12

20

08

-18

20

08

-24

20

08

-30

20

08

-36

20

08

-42

20

08

-48

20

09

-01

20

09

-07

20

09

-13

20

09

-19

20

09

-25

20

09

-31

20

09

-37

20

09

-43

20

09

-49

20

10

-03

20

10

-09

20

10

-15

20

10

-21

20

10

-27

20

10

-33

20

10

-39

20

10

-45

20

10

-51

20

11-0

5

Nu

mb

er

of

de

ath

s

Week of Death

2007-08

Number of Deaths Reported = 88

2008-09

Number of Deaths Reported = 133

2009-10

Number of Deaths Reported = 282

Deaths Reported Current WeekDeaths Reported Previous Week

2010-11

Number of Deaths Reported = 35

Number of Influenza-Associated Pediatric Deaths by Week of Death: 2007-08 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 2010-2011 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