Influenza Activity Update

Lyn Finelli, DrPH, MSLead, Influenza Surveillance and Outbreak Response Team

Epidemiology BranchInfluenza Division

VRBACFebruary 27, 2013

VIROLOGIC SURVEILLANCE

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

10

20

30

40

50

H3N2v

2009 H1N1

A(H3)

A(Subtyping not performed)

B

Percent Positive

Week

Nu

mb

er

of

Po

sit

ive

Sp

ec

ime

ns

Pe

rce

nt

Po

sit

ive

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

February 16, 201316.8%

38.1%

Antigenic CharacterizationSeptember 30, 2012 – February 16, 2013

Influenza A 2009 H1N1

• 86/86 (100%) characterized A/California/7/2009-like, the H1N1 component of the 2012-13 N. Hemisphere vaccine

H3N2• 740/744 (99.5%) characterized as A/Victoria/361/2011-like

the H3N2 component of the 2012-13 N. Hemisphere vaccine

Influenza B Yamagata lineage

• 251/355 (71%) are from the Yamagata lineage and characterized as B/Wisconsin/1/2010-like the influenza B component of the 2012-13 N. Hemisphere vaccine

Victoria lineage • 104/355 (29%) tested have been from the Victoria lineage

of viruses

Antiviral ResistanceSeptember 30, 2012 – February 16, 2013

High levels of resistance to the adamantanes (amantadine and rimantadine) persist among pH1N1 and influenza A (H3N2) viruses currently circulating globally.

Neuraminidase Inhibitor Resistance Testing Results Samples Collected Since September 30, 2012

Oseltamivir ZanamivirVirus

Samples tested

(n)

Resistant Viruses, Number

(%)

Virus Samples tested

(n)

Resistant Viruses, Number

(%)Influenza A (H3N2) 1,193 0 (0.0) 1,193 0 (0.0)

Influenza B 419 0 (0.0) 419 0 (0.0)2009 H1N1 274 2 (0.9) 114 0 (0.0)

ILI SYNDROMIC SURVEILLANCE

ILINet Coverage

0

1

2

3

4

5

6

7

8

Week

% o

f V

isit

s f

or

ILI

2012-13 (current season)2011-12 (mild season)2009-10 (pandemic)2007-08 (moderately severe season)2003-04 (moderately severe season)2002-03 (moderate season)National Baseline

Percentage of Visits for Influenza-like Illness Influenza-like Illness Surveillance Network (ILINet),

2012-13 and Selected Previous Seasons

February 16, 20132.8%

6.1%

7.6%

Relative Influenza-like Illness Activity Indicator as Determined by ILINet Provider Reports, February 16, 2013

HOSPITALIZATION SURVEILLANCE

Rates of Laboratory-Confirmed Influenza Hospitalization by Age Group FluSurvNet, September 30 2012 – February 16,

2013

2012

MORTALITY SURVEILLANCE

2009

-40

2009

-44

2009

-48

2009

-52

2010

-04

2010

-08

2010

-12

2010

-16

2010

-20

2010

-24

2010

-28

2010

-32

2010

-36

2010

-40

2010

-44

2010

-48

2010

-52

2011

-04

2011

-08

2011

-12

2011

-16

2011

-20

2011

-24

2011

-28

2011

-32

2011

-36

2011

-40

2011

-44

2011

-48

2011

-52

2012

-04

2012

-08

2012

-12

2012

-16

2012

-20

2012

-24

2012

-28

2012

-32

2012

-36

2012

-40

2012

-44

2012

-48

2012

-52

2013

-04

2013

-08

0

5

10

15

20

25

30

35

40

Week of Death

Nu

mb

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of

de

ath

s

Newly Reported DeathsPreviously Reported Deaths

Number of Influenza-Associated Pediatric Deaths by Week of Death

2009–10 season to February 16, 2013

2009-10

Number of Deaths Reported = 282

2010-11

Number of Deaths Reported = 122

2011-12

Number of Deaths Reported = 34

2012-13

Number of Deaths Reported = 78

10 20 30 40 50 10 20 30 40 50 10 20 30 40 50 10 20 30 40 50 10 20 30 40 504

6

8

10

12

Weeks

% o

f A

ll D

ea

ths

Du

e t

o P

&I

9.9%

Epidemic Threshold

Seasonal Baseline

Pneumonia and Influenza Mortality in 122 U.S. Cities

2007–08 to February 16, 2013

2008 2009 2010 2011 2012 2013

Why Did We Have So Much Flu This Season?

Different H3N2 strain compared to last year A/Vic/361-like viruses that are circulating this year are

different from the previous antigenic variant A/Perth/09.   The Perth/09 circulated from April 09 until last year. 

Intensity of influenza activity has been overall fairly low in the last two seasons.  When we have a few successive years without intense H3N2 activity we have more susceptibles

H3N2 seasons are always more “severe” and cause more hospitalizations and deaths than either influenza B or H1N1

Even if the vaccine is antigenically similar, only ~50% of population is vaccinated leaving half of all Americans unprotected

Influenza Activity Summary

Influenza activity in the US during the 2012–13 season began approximately 4 weeks earlier than usual, and occurred at moderately high levels Activity increased in late November and peaked in late

December Activity continues in much of the country especially the

west Influenza A (H3N2) viruses have predominated overall,

but influenza B viruses have also circulated This influenza season has been moderately severe with

high rates of influenza hospitalization and a large proportion of deaths attributed to pneumonia and influenza in seniors

Mid-season Adjusted Estimates of Seasonal Influenza Vaccine

Effectiveness — United States, February 2013

Mark Thompson, Ph.D.Influenza Division

ACIPFebruary 21, 2013

National Center for Immunization & Respiratory Diseases

Influenza Division

US Flu VE Network: Five Study Sites and Principal Investigators

Lisa JacksonMike Jackson

Ed Belongia

Arnold MontoSuzanne Ohmit

Rick ZimmermanPatricia Nowalk

Manju Gaglani

US Flu VE Network: Methods Purpose: Estimate VE for prevention of outpatient

healthcare visits due to influenza Design: Prospective case-control study

Cases: Medically attended ARI and RT-PCR influenza Controls: Medically attended ARI but negative for

influenza Interim vaccination status: Confirmed by medical

record or registry (3 sites) and by self-report (2 sites) Immunization: 1+ dose of vaccine ≥14 from illness

onset Analysis: VE = (1 – adjusted OR) x 100%

Standard covariates: age, site, and days from illness onset to enrollment

Adjusted for potential confounding by race/ethnicity and self-rated health

Cases enrolled by (sub)type to date

Among the 751 influenza A virus infections, 560 (75%) have been subtyped to date; 546 (98%) were due to A(H3N2) viruses.

Influenza B; 366

Influenza A(H1N1)pdm; 14

Influenza A(H3N2); 546

Influenza A sub-type pending; 191

Mid-season adjusted VE (95% CI) against A and B

6 mo. - 17 years

18-49 years

50-64years

65+ years

Interim Season 2012-13

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

Mid-season adjusted VE (95% CI) against A(H3N2) only and B only by age

6 mo. – 17 years

(179; 565)

18 – 49 years(183; 604)

50-64 years

(96; 248)

65+ years

(86; 165)

6 mo. – 17 years(59; 565)

18 – 49 years

(17; 604)

50-64 years

(8; 248)

65+ years

(6; 165)Influenza A(H3N2) only Influenza B only

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Age:(cases; controls)

Conclusions Adjusted VE against influenza A and B was 56% (47-

63%)

• Similar to earlier unadjusted VE of 62% (51-71%) against A and B

Vaccination reduced the risk of outpatient medical visits:

• Due to influenza A(H3N2) by half (47%); consistent for ages <65

• Due to influenza B by two-thirds (67%); consistent for all ages

Similar to other interim estimates from this season

• Canada: VE against A(H3N2) = 45% (13%–66%)

• UK: VE against A = 49% (-2%-75%) and against B = 52% (23%-70%)

• I-MOVE: VE against A and B = 62% (21%-82%)

Conclusions Sub-optimal VE against A(H3N2) among adults aged

65+

• Similar to interim VE against A(H3N2) among elderly in Denmark

Limits and next steps

• Pending full enrollment from entire season

• Missing chronic medical conditions, vaccine type, and prior vaccination status until final data set

• Additional potential confounders will be considered Implications

• Vaccination beneficial, especially among younger age groups

• Need more effective vaccines and vaccination strategies

• Need better understanding of factors that modify VE

Acknowledgements - Surveillance

Lynnette BrammerJoseph BreseeScott EppersonLenee BlantonKrista KnissRosaline DharaDesiree MustaquimTiffany D’MelloAlejandro PerezAndrea GiorgiCraig SteffensAshley FowlkesJulie Villanueva

Michael JhungCarrie ReedAlicia FrySeema JainAnna BramleyVictoria JiangSandra Dos Santos ChavesDaniel JerniganJoe GreggLarisa GubarevaTerri WallaceXiyan XuNancy Cox

Acknowledgments -- VE

CDC: Alicia Fry, Mark Thompson, Swathi Thaker, Jill Ferdinands, Po-Yung Cheng, Sarah Spencer, Erin Burns, LaShondra Berman, David Shay, Joseph Bresee, Nancy Cox

Group Health: Lisa Jackson, Mike Jackson

Marshfield: Ed Belongia

Scott & White: Manju Gaglani

U Michigan: Arnold Monto, Suzanne Ohmit

U Pittsburgh: Rick Zimmerman, Tricia Nowalk

Thank you

LFinelli@cdc.gov

www.cdc.gov/flu

http://www.cdc.gov/flu/weekly/fluviewinteractive.htm

VRBAC February 27, 2013

Influenza Division, National Center for Immunization and Respiratory Diseases

Numbers of influenza-positive medically attended ARI cases (orange bars) and influenza-negative controls

(blue bars) by week of illness onset

Week 3 only includes patients with completed laboratory tests and thus does not reflect all enrolled patients during that week across study sites.

49 50 51 52 1 2 30

50

100

150

200

250

300

350

400

27

81

126

192215

325

149

112

198181

234

321348

188CasesControls

MMWR Week, 2012-13

Nu

mb

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En

roll

ed

Mid-season adjusted VE against A and B

   

Influenza and Vaccination Status   Vaccine EffectivenessInfluenza-Positive

CasesInfluenza-Negative

Controls  Adjusted †

No. Vaccinated

/Total

 (%)

No. Vaccinated

/Total

 (%)

  

(%) 

(95% CI)

Influenza A and B               All ages 367/1115 (32) 793/1582 (50)   (56) (47-63)                6 mo. – 17 years 118/463 (26) 275/565 (49)   (64) (51-73)

18 – 49 years 100/353 (28) 256/604 (42)   (52) (38-79) 50-64 years 63/174 (36) 143/248 (58)   (63) (43-76) 65+ years 86/125 (69) 119/165 (72)   (27) (-31,59)               

† Vaccine effectiveness was estimated as 100% X (1 – odds ratio [ratio of odds of being vaccinated among the cases to the odds of being vaccinated among the controls]) using logistic regression.

Multivariate models adjusted for age, race/ethnicity, study site, days from illness onset to enrollment, and self-rated health status. For the all ages models, age was represented as categories; age in years

was used in age-stratified models.

Mid-season VE against A(H3N2) only and B only by age

   Virus and age groups

Influenza and Vaccination Status   Vaccine EffectivenessInfluenza-Positive

CasesInfluenza-Negative

Controls  Adjusted †

No. Vaccinated /Total

 (%)

No. Vaccinated

/Total

 (%)

   (%)

 (95% CI)

Influenza A(H3N2) only              

All ages 211/544 (39) 793/1582 (50)   (47) (35-58)                6 mo. – 17 years 52/179 (29) 275/565 (49)   (58) (38-71)

18 – 49 years 53/183 (29) 256/604 (42)   (46) (20-63) 50-64 years 41/96 (43) 143/248 (58)   (50) (15-71) 65+ years 65/86 (76) 119/165 (72)   (9) (-84, 55)

               Influenza B only               All ages 90/364 (25) 793/1582 (48)   (67) (51-78)                6 mo. – 17 years 59/230 (26) 275/565 (49)   (64) (46-75)

18 – 49 years 17/79 (22) 256/604 (42)   (68) (40-83) 50-64 years 8/40 (20) 143/248 (58)   (75) (39-90) 65+ years 6/15 (40) 119/165 (72)   (67) (-10, 90)

† Adjusted for age, site, race/ethnicity, self-rated health, and days from onset

Adjusted VE (95% CI) against circulating strains by season in US Flu

VE Network6

mo

. -

2ye

ars 3-8

ye

ars

9-4

9

ye

ars

50

-64

ye

ars

65

+

ye

ars

6 m

o.

- 8

ye

ars

9-1

7

ye

ars

18

-49

ye

ars

50

-64

ye

ars

65

+

ye

ars

6 m

o.

- 1

7

ye

ars

18

-49

ye

ars

50

-64

ye

ars

65

+

ye

ars

Season 2010-11 Season 2011-12 Interim Season 2012-13

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

Previous seasons using this platform have estimated higher VE in elderly

4

6

8

10

12

% o

f A

ll D

eath

s D

ue t

o P

&I

A(H3) A(H1) B 2009 A(H1)

* 2008-09 season = wk 40, 2008 – wk 34, 2009

** 2009-10 season starts at wk 35, 2009

A(H3N2v)

Pneumonia and Influenza Mortalityfor 122 U.S. Cities

Through February 16, 2013

95-96 96-97 97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 05-06 07-0806-07 08-09* 09-10** 11-12 12-1310-11

MMWR. 2010 Aug 27;59(33):1057-62.