CDC Influenza Division Key Points MMWR Updates February 20, 2014

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1 CDC Influenza Divisin Key Pints MMWR Updates In this dcument: Summary Key Messages Seasnal Influenza Vaccine Effectiveness: Interim Adjusted Estimates Influenza Surveillance Update: September 29, 2013-February 8, 2014 Summary Key Messages On, CDC published interim adjusted estimates n hw well the influenza vaccine prtected against having t g t the dctr fr flu this seasn. The MMWR reprt is available n the CDC website at In the same MMWR, CDC published a secnd reprt with a surveillance update n flu activity in the United States s far this seasn. The reprt entitled MMWR Update: Influenza Activity United States, September 29, 2013 February 8, 2014 is available at A reprt n severe influenza illness amng Califrnia residents yunger than 65 years was als published in the MMWR. The reprt, Influenza-Assciated Intensive-Care Unit Admissins and Deaths Califrnia, September 29, 2013-January 18, 2014, is available at The VE study results indicate that influenza vaccinatin ffered substantial prtectin against the flu this seasn, reducing a vaccinated persn s risk f having t g t the dctr fr flu illness by abut 61% acrss all ages. VE estimates against influenza A and B ranged frm 52% fr peple 65 and lder t 67% fr children 6 mnths t 17 years. Mre specifically, VE estimates against this seasn s predminant H1N1 strain ranged frm 56% in peple 65 and lder t 67% fr children 6 mnths t 17 years. The interim VE estimates this seasn are cmparable t results frm studies during ther seasns when the viruses in the vaccine have been well-matched with circulating influenza viruses. The estimates als are similar t interim estimates frm Canada fr published recently. While flu vaccine can vary in hw well it wrks, vaccinatin ffers the best prtectin currently available against influenza infectin. CDC recmmends that everyne 6 mnths and lder get an annual flu vaccine. 1

2 CDC Influenza Divisin Key Pints - MMWR Updates The VE study results shw that vaccinated peple were substantially better ff this seasn than peple wh did nt get vaccinated. The surveillance reprt highlights the predminance f the 2009 H1N1 flu virus this seasn and the high prprtins f flu hspitalizatins and deaths that have ccurred in yunger- and middle-aged adults this seasn. Of the hspitalizatins reprted t CDC this seasn, 61% have been in peple 18 t 64 years ld. Mre cmmnly, mst flu hspitalizatins ccur in peple 65 and lder. Usually 50-60% f flu hspitalizatins ccur in peple aged 65 years and lder. Additinally, this seasn, peple 25 years t 64 years f age have accunted fr abut 60% f flu deaths cmpared with 18%, 30%, and 47% fr the three previus seasns respectively. During , peple 25 years t 64 years accunted fr an estimated 63% f deaths. These hspitalizatins and deaths are a smber reminder that flu can be serius fr anyne nt just the very yung and peple aged 65 and lder and underscres the imprtance f vaccinatin fr everyne. Unfrtunately, yunger adults especially thse wh are therwise healthy are less likely t get vaccinated. Estimates as f early-nvember 2013 indicate that amng peple years f age, nly 34% had been vaccinated. This vaccine cverage estimate is lwer than vaccine cverage estimates fr peple aged 6 mnths-17 years f age (41%) and peple 65 and lder (62%) in the U.S. during that same time perid. Seasnal flu is respnsible fr severe illness and death every year, but wh is mst affected each seasn can vary depending n the predminant circulating virus. This seasn s pattern f higher levels f flu-related deaths and hspitalizatins amng yunger and middle-aged adults is similar t what was seen in 2009 when the H1N1 virus emerged t cause a pandemic. Fr example, a reprt in tday s MMWR describes the epidemilgic, labratry, and clinical characteristics f 405 severe influenza cases (94 influenza-assciated deaths and 311 intensive care unit [ICU] admissins) amng Califrnia residents yunger than 65 years ld as reprted t the Califrnia Department f Public Health (CDPH). The number f fatal and ICU cases reprted t the CDPH as f January 18, 2014 is mre than has been recrded in any seasn since the 2009 pandemic. Of 405 ICU and fatal influenza cases, 266 (66%) ccurred amng patients aged years; 39 (10%) severe influenza illnesses ccurred amng children aged <18 years. 2

3 CDC Influenza Divisin Key Pints - MMWR Updates The majrity f patients with fatal illness tested psitive fr 2009 H1N1 virus, suffered frm underlying medical cnditins that predispsed them t severe influenza cmplicatins (mst cmmnly diabetes, COPD, asthma and mrbid besity), and had nt received seasnal influenza vaccine. The 2009 H1N1 virus has cntinued t circulate since the pandemic as a seasnal flu virus, but this is the first flu seasn since the pandemic that this virus has circulated s widely. All flu vaccines this seasn are designed t prtect against H1N1 and VE against H1N1 this seasn was estimated t be 62% fr all age grups. At this time, even with a recent decrease in several key indicatrs, influenza activity remains elevated verall natinally and is expected t cntinue fr a number f weeks in certain parts f the cuntry. Annual influenza vaccinatin effrts shuld cntinue fr as lng as influenza viruses are circulating. Influenza vaccinatin is especially imprtant fr peple at high risk fr serius flu cmplicatins including: peple with underlying chrnic medical cnditins such as asthma, diabetes, heart disease, r neurlgical cnditins; pregnant wmen; thse yunger than 5 years r lder than 65 years f age; r anyne with a weakened immune system. A full list f high risk factrs is available at While vaccinatin is the first and best way t prevent flu, CDC recmmends antiviral medicatins as a secnd line f defense t treat influenza in certain patients, regardless f vaccinatin status. Antiviral treatment can avert serius utcmes and shuld begin as quickly as pssible in high risk persns, including peple 65 and lder, yung children, pregnant wmen, and peple with certain underlying cnditins like asthma, heart disease, diabetes and neurlgical disrders. A health care prvider can determine if the patient needs influenza antiviral drugs. These drugs wrk best when started sn after influenza symptms begin (within 2 days), but bservatinal studies have shwn that giving antivirals 48 r mre hurs after symptm nset can still prevent serius flu-related utcmes. In additin t vaccinatin and antiviral drugs, everyday preventive actins can help mitigate the risk f infectin. Flu spreads mainly in drplets expelled when peple with flu cugh, sneeze r talk. As always, stay away frm peple wh are sick. If yu are sick, stay hme t avid spreading yur illness t thers. 3

4 CDC Influenza Divisin Key Pints - MMWR Updates At this pint in the seasn, peple may have t check with mre than ne vaccine prvider in rder t lcate vaccine, but supplies f vaccine shuld still be available. CDC rutinely recmmends that vaccinatin effrts cntinue as lng as influenza viruses are circulating. Peple seeking vaccinatin may need t call mre than ne prvider t lcate vaccine at this time. The flu vaccine finder at may be helpful. MMWR: Interim Estimates f Seasnal Influenza Vaccine Effectiveness United States, February 2014 CDC recmmends influenza vaccinatin as the first step t prevent illness caused by flu viruses. As f February 8, 2014, influenza activity was still elevated acrss mst f the United States. On February 21, 2014, CDC published a reprt f interim adjusted estimates f influenza vaccine effectiveness (VE) in the Mrbidity and Mrtality Weekly Reprt (MMWR) entitled: Interim Estimates f Seasnal Influenza Vaccine Effectiveness United States, February The MMWR reprt is available at Data cllected frm 2,319 children and adults were used t estimate the verall effectiveness f seasnal influenza vaccine fr preventing utpatient medicallyattended acute respiratry infectin (ARI). The utpatients were enrlled at five study sites acrss the United States thrugh the U.S. Influenza Vaccine Effectiveness (Flu VE) Netwrk. CDC reprted an verall vaccine effectiveness f 61% (95% cnfidence interval [CI]:52% t 68%) against any influenza infectin. This estimate was adjusted fr study site, age, sex, race/ethnicity, self-rated health and days frm illness nset t enrllment. These findings indicate that vaccinatin with the influenza seasn vaccine reduced the risk f utpatient medical visits due t influenza by apprximately 60% fr children and adults. An adjusted VE estimate f 62% (CI=53% t 69%) against 2009 H1N1 influenza viruses was reprted. While ther studies have fund that the flu vaccine generally appeared t wrk best amng healthy adults and lder children, similar vaccine effectiveness against 2009 H1N1 was bserved amng all age grups in this study. 4

5 CDC Influenza Divisin Key Pints - MMWR Updates During the study perid, 2009 H1N1 influenza viruses accunted fr 98% f the influenza viruses detected. This is the H1N1 virus that emerged in 2009 t cause a pandemic. This virus has cntinued t circulate since the pandemic as a seasnal flu virus, but this is the first flu seasn since the pandemic that 2009 H1N1 has circulated s widely. These interim adjusted VE estimates against 2009 H1N1 medically-assciated utpatient visits are cmparable t VE estimates measured fr mnvalent 2009 H1N1 vaccine during the H1N1 pandemic and fr seasnal vaccines in years when the vaccine is well-matched t circulating strains. These interim VE estimates fr the seasnal influenza vaccine suggest cntinued effectiveness in preventing utpatient medical visits assciated with 2009 H1N1 virus infectin. The prtective benefits f the influenza vaccine amng children and adults shwn in this reprt ffer supprt t the public health benefit f the universal recmmendatin fr annual vaccinatin with the seasnal influenza vaccine. T date, despite a decrease in several key indicatrs, influenza activity remains elevated verall natinally and is expected t cntinue fr several weeks in certain parts f the cuntry. Annual influenza vaccinatin effrts shuld cntinue fr as lng as influenza viruses are circulating. These interim estimates, hwever, indicate that sme vaccinated persns will becme infected with influenza despite having been vaccinated. Therefre, clinicians and the public are reminded f CDC s influenza antiviral treatment recmmendatins. Antiviral medicatins shuld be used as recmmended fr treatment in patients, regardless f vaccinatin status. See the CDC website fr mre infrmatin at Influenza Antiviral Medicatins: Summary fr Clinicians (fr health care prviders) and What Yu Shuld Knw abut Flu Antiviral Drugs (fr the public). CDC will cntinue t mnitr VE thrughut the seasn and will publish final VE estimates fllwing the cnclusin f the seasn. The final, adjusted vaccine effectiveness estimates fr the influenza vaccine are likely t be smewhat different frm the current interim estimates fr a number f reasns, including adjustments fr additinal ptential cnfunders, such as chrnic medical cnditins in patients, which are nt available fr interim estimates. VE estimates culd als change as mre patient data becme available, r if changes ccur in the circulating influenza viruses during the remainder f this seasn. 5

6 CDC Influenza Divisin Key Pints - MMWR Updates Other Results Acrss study sites, the prprtin f enrllees vaccinated with influenza seasnal vaccine was 29% amng influenza cases cmpared with 50% amng influenza-negative cntrls. Of the 2,319 children and adults with ARI enrlled at the study sites, 784 (34%) tested psitive fr influenza by rrt-pcr. Of these, 778 (99%) were influenza A viruses and 6 (1%) were influenza B viruses. Amng 755 subtyped influenza A viruses, 742 (98%) were 2009 H1N1 viruses. The 2009 H1N1 viruses tested by CDC this seasn, including viruses frm the U.S. VE Flu Netwrk study sites, have been antigenically similar t A/Califrnia/7/2009, the H1N1 cmpnent f the influenza vaccines. Sequencing analyses f H1N1 virus specimens have als shwn similarity t the recmmended vaccine virus. Methdlgy Frm December 2, 2013 t January 23, 2014, patients aged 6 mnths and lder wh sught utpatient medical care fr an ARI with cugh, within 7 days f illness nset, were enrlled at five study sites within the U.S. Flu VE Netwrk. Study enrllment began at each site after at least tw cnsecutive weeks f labratry-cnfirmed cases f influenza had been identified thrugh lcal surveillance. Patients were eligible fr enrllment if they: 1) were aged 6 mnths n September 1, 2013, and thus were eligible fr vaccinatin; 2) reprted an ARI with nset 7 days prir t their visit; and 3) had nt been treated with influenza antiviral medicatin (e.g. seltamivir) during this illness. Respiratry specimens were cllected frm each patient using nasal and/r rpharyngeal swabs (nly nasal swabs were cllected frm children 2 years ld and yunger). Specimens were tested at U.S. flu VE Netwrk labratries using CDC s real-time reverse transcriptin plymerase chain reactin (rrt-pcr) prtcl fr detectin and identificatin f influenza viruses. Participants were cnsidered vaccinated if they received at least ne dse f any seasnal influenza vaccine 14 days prir t illness nset, accrding t medical recrds and registries (at tw sites) r self-reprt and medical recrds (at three sites). 6

7 CDC Influenza Divisin Key Pints - MMWR Updates VE was estimated by cmparing the dds f vaccinatin amng influenza-psitive (cases) versus influenza-negative (cntrls) participants. Estimates were adjusted fr study site, age, sex, race/ethnicity, self-rated health and days frm illness nset t enrllment using lgistic regressin. Backgrund CDC cnducts studies t measure the benefits f seasnal flu vaccinatin each flu seasn t help determine hw well flu vaccines are wrking. These studies are called vaccine effectiveness studies r VE studies, fr shrt. Hw well the flu vaccine wrks can vary by seasn, virus type/subtype, the vaccine, and age and ther hst factrs f the peple being vaccinated. VE is difficult t measure and study results can vary widely based n the study design, the utcme being measured and the ppulatin being studied. CDC has wrked with researchers at universities and health systems since t estimate VE in nn-randmized, bservatinal studies. The U.S. Flu VE Netwrk cnsists f five study sites acrss the United States that measure the flu vaccine s effectiveness at preventing utpatient medical visits due t labratry-cnfirmed influenza. CDC s bservatinal studies at U.S. Flu VE Netwrk sites measure utpatient visits fr labratry-cnfirmed influenza infectin using a highly accurate lab test called rrt-pcr t verify the utcme. This is an bservatinal study that cmpares the dds f vaccinatin amng utpatients with acute respiratry illness and labratry-cnfirmed influenza infectin t the dds f vaccinatin amng utpatients with ARI wh test negative fr influenza infectin. The study uses a test-negative cntrl design, which minimizes ptential bias intrduced by access t medical care and health care-seeking behavir. MMWR Update: Influenza Activity United States, September 29, 2013 February 8, 2014 The February 21, 2014 Mrbidity and Mrtality Weekly Reprt (MMWR) cntains a summary f influenza activity in the United States fr September 29, 2013 February 8, The MMWR reprt is available n the CDC website at 7

8 CDC Influenza Divisin Key Pints - MMWR Updates Key bservatins include the fllwing: Influenza activity in the United States began increasing in Nvember and remained elevated and widespread as f February 8. This seasn, influenza activity began t increase in the suthern states and, by the end f December, high influenza activity was seen thrughut the cuntry. Since the start f the seasn, influenza A (H1N1)pdm09 (ph1n1) viruses have predminated in the United States. Influenza A (H3N2) viruses and influenza B viruses have been identified less frequently. This influenza A (H1N1) virus is the same virus that was first identified in 2009 and which caused the 2009 influenza pandemic. The vast majrity f influenza viruses characterized s far this flu seasn have been like the viruses in the Nrthern Hemisphere influenza vaccine. Influenza viruses have been a significant cause f respiratry illness this flu seasn. Between September 29 and February 8, f the 189,123 respiratry specimens that were tested fr influenza, 19% were influenza-psitive. This seasn, the percentage f utpatient visits t dctrs fr influenza-like illness (ILI) equaled r exceeded the natinal baseline f 2.0% frm the week ending Nvember 30, 2013 t February 8, 2014 and has ranged frm 1.2% t 4.6% since September 29, During the thrugh seasns (excluding the 2009 pandemic), peak weekly percentages f utpatient visits fr ILI ranged frm 2.4% t 7.6%. Fr the week ending February 8, 2014 (week 6), all 10 regins reprted ILI activity abve their regin-specific baseline levels. This is the furteenth week this seasn during which ne r mre regins exceeded their regin-specific baselines. Resistance t the antiviral drugs seltamivir and zanamivir amng currently circulating influenza viruses is lw. Since Oct 1, 2013, the vast majrity f influenza viruses tested have shwn susceptibility t antiviral drugs seltamivir and zanamivir. Of the 3,109 ph1n1 viruses tested fr antiviral resistance, 25 were fund t be resistant t seltamivir. N viruses have shwn resistance t zanamivir. All influenza A (H3N2) and influenza B viruses tested fr antiviral resistance were sensitive t bth seltamivir and zanamivir. Between September 29 and February 8, the weekly percentage f deaths attributed t pneumnia and influenza (P&I) ranged frm a lw f 5.3% t a high f 8.7% (week 4). As f the week ending February 8, the weekly 8

9 CDC Influenza Divisin Key Pints - MMWR Updates percentage f deaths had exceeded the epidemic threshld fr five cnsecutive weeks (beginning with the week ending January 11, 2014). Peak weekly percentages f deaths attributed t P&I in the previus five seasns range 7.9% during the and seasns t 9.9% in the seasn. As f February 8, 2014 (week 6), 50 influenza-related pediatric deaths were reprted t CDC fr the seasn. One pediatric death was assciated with an influenza B virus, tw deaths were assciated with an influenza virus fr which the type was nt determine, ne death was assciated with an influenza A and influenza B virus c-infectin,17 deaths were assciated with influenza A virus infectin that was nt subtyped, and 29 deaths were assciated with ph1n1 viruses. Between Octber 1 and February 8, 24.6 hspitalizatins per 100,000 were assciated with labratry-cnfirmed influenza. Peple 65 years and lder had the highest influenza-assciated hspitalizatin rate (50.9 per 100,000), fllwed by adults years (38.7 per 100,000). As f February 8, 61.2% f the reprted hspitalizatins have been in peple 18 t 64 years ld, while 24.8% f hspitalizatins have ccurred in adults 65 years and lder. Mre cmmnly, mst flu hspitalizatins ccur in peple 65 years and lder. The mst cmmnly reprted underlying medical cnditins amng children (thse aged <18 years) hspitalized with influenza were asthma (24%), neurlgic disrders (13%), besity (10%), and chrnic lung disease (excluding asthma) (8%). Frty-three percent f hspitalized children had n underlying medical cnditins that place them at higher risk fr flu-related cmplicatins. The mst cmmnly reprted chrnic underlying medical cnditins in adults were besity (43%), metablic disrders (33%), cardivascular disease (29%), and chrnic lung disease (excluding asthma) (27%); fifteen percent f hspitalized adults had n underlying medical cnditins that place them at higher risk fr flu-related cmplicatins. Amng 301 hspitalized wmen f childbearing age (15 44 years), 65 (22%) were pregnant. Additinal Infrmatin This is the first seasn since the 2009 pandemic that ph1n1 has been the predminant influenza virus circulating in the United States. 9

10 CDC Influenza Divisin Key Pints - MMWR Updates During the pandemic, when ph1n1 viruses were predminant, yunger adults and children, and particularly peple with chrnic medical cnditins, were harder hit by flu cmpared with adults aged 65 years and lder. Peple aged years have accunted fr apprximately 62% f all influenzaassciated deaths s far this seasn, cmpared with 18% in , 30% in , 47% in The mre severe impact f ph1n1 n adults aged years is thught t result frm at least tw factrs: Persns in these age grups likely lack the crss-reactive immunity t ph1n1 that adults aged 65 years have acquired frm past infectin with antigenically related viruses. In general, CDC estimates yunger adults especially thse wh are therwise healthy are less likely t get vaccinated. Surveillance data available frm this seasn are a reminder that influenza can cause severe illness, even in adults aged years. Vaccinatin is the best way t prevent influenza and its cmplicatins and is recmmended annually fr all persns aged 6 mnths and lder. Antiviral treatment can avert serius utcmes and shuld begin as quickly as pssible in persns with severe disease r in ther persns at high risk f cmplicatins, including peple 65 and lder, yung children, pregnant wmen, and peple with certain underlying cnditins like asthma, heart disease, diabetes and neurlgical disrders. While antiviral drugs wrk best when given within 48 hurs f symptm nset, bservatinal studies have shwn that giving antivirals 48 r mre hurs after symptm nset can still prevent serius flu-related utcmes. 10