Influenza Activity Update Lyn Finelli, DrPH, MS Lead, Influenza Surveillance and Outbreak Response Team Epidemiology Branch Influenza Division VRBAC February 27, 2013

VIROLOGIC SURVEILLANCE

Antigenic Characterization September 30, 2012 – February 16, 2013  Influenza A  2009 H1N1 86/86 (100%) characterized A/California/7/2009-like, the H1N1 component of the N. Hemisphere vaccine  H3N2 740/744 (99.5%) characterized as A/Victoria/361/2011-like the H3N2 component of the 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 N. Hemisphere vaccine  Victoria lineage 104/355 (29%) tested have been from the Victoria lineage of viruses

Antiviral Resistance September 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 OseltamivirZanamivir Virus Samples tested (n) Resistant Viruses, Number (%) Virus Samples tested (n) Resistant Viruses, Number (%) Influenza A (H3N2) 1,1930 (0.0)1,1930 (0.0) Influenza B4190 (0.0)4190 (0.0) 2009 H1N12742 (0.9)1140 (0.0)

ILI SYNDROMIC SURVEILLANCE

ILINet Coverage

Percentage of Visits for Influenza-like Illness Influenza-like Illness Surveillance Network (ILINet), and Selected Previous Seasons February 16, % 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 – February 16,

MORTALITY SURVEILLANCE

Newly Reported DeathsPreviously Reported Deaths Number of Influenza-Associated Pediatric Deaths by Week of Death 2009–10 season to February 16, Number of Deaths Reported = Number of Deaths Reported = Number of Deaths Reported = Number of Deaths Reported = 78

Epidemic Threshold Seasonal Baseline Pneumonia and Influenza Mortality in 122 U.S. Cities 2007 – 08 to February 16,

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 ACIP February 21, 2013 National Center for Immunization & Respiratory Diseases Influenza Division

US Flu VE Network: Five Study Sites and Principal Investigators Lisa Jackson Mike Jackson Ed Belongia Arnold Monto Suzanne Ohmit Rick Zimmerman Patricia 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.

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

Mid-season adjusted VE (95% CI) against A(H3N2) only and B only by age 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 Brammer Joseph Bresee Scott Epperson Lenee Blanton Krista Kniss Rosaline Dhara Desiree Mustaquim Tiffany D’Mello Alejandro Perez Andrea Giorgi Craig Steffens Ashley Fowlkes Julie Villanueva Michael Jhung Carrie Reed Alicia Fry Seema Jain Anna Bramley Victoria Jiang Sandra Dos Santos Chaves Daniel Jernigan Joe Gregg Larisa Gubareva Terri Wallace Xiyan Xu Nancy 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 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.

Mid-season adjusted VE against A and B Influenza and Vaccination Status Vaccine Effectiveness Influenza-Positive Cases Influenza-Negative Controls Adjusted † No. Vaccinated /Total (%) No. Vaccinated /Total (%) (%) (95% CI) Influenza A and B All ages367/1115(32)793/1582(50) (56)(47-63) 6 mo. – 17 years118/463(26)275/565(49) (64)(51-73) 18 – 49 years100/353(28)256/604(42) (52)(38-79) years63/174(36)143/248(58) (63)(43-76) 65+ years86/125(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 Effectiveness Influenza-Positive Cases Influenza-Negative Controls Adjusted † No. Vaccinated /Total (%) No. Vaccinated /Total (%) (%) (95% CI) Influenza A(H3N2) only All ages211/544(39)793/1582(50) (47)(35-58) 6 mo. – 17 years52/179(29)275/565(49) (58)(38-71) 18 – 49 years53/183(29)256/604(42) (46)(20-63) years41/96(43)143/248(58) (50)(15-71) 65+ years65/86(76)119/165(72) (9)(-84, 55) Influenza B only All ages90/364(25)793/1582(48) (67)(51-78) 6 mo. – 17 years59/230(26)275/565(49) (64)(46-75) 18 – 49 years17/79(22)256/604(42) (68)(40-83) years8/40(20)143/248(58) (75)(39-90) 65+ years6/15(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 Network Previous seasons using this platform have estimated higher VE in elderly

A(H3)A(H1)B 2009 A(H1) * season = wk 40, 2008 – wk 34, 2009 ** season starts at wk 35, 2009 A(H3N2v) Pneumonia and Influenza Mortality for 122 U.S. Cities Through February 16, *09-10**

MMWR Aug 27;59(33):