CDC Influenza Division Key Points

In this document:

• Summary Key Points

• FluView Activity Update

• Influenza-Associated Pediatric Deaths

• Influenza-Associated Hospitalizations

Summary Key Points

• Flu activity remains low across most of the United States.

• The latest FluView report shows some key flu indicators falling, while others are increasing slowly. Reports of influenza-like-illness fell below the national baseline this week, however, it is likely to rise again. (See section "FluView Activity Update" for more information.)

• The U.S. flu season is beginning.

• Recent flu seasons have started relatively early. The timing of the current flu season so far is more typical. Most often flu peaks during the month of February.

• While flu seasons vary in their timing, duration and intensity, it is likely that there are still many weeks of flu activity to come.

• While influenza A (H3N2) viruses have been most common since October 1, but during recent weeks influenza A (H1N1) viruses have been predominant.

• Laboratory data so far show that most circulating flu viruses are still like the viruses recommended for the 2015-2016 influenza vaccines.

• The similarity between vaccine viruses and circulating viruses is one factor that can influence how well the vaccine works.

• With most of the flu season still to come, getting a flu vaccine now can still protect you from illness this season.

• Each flu season, flu causes millions of illnesses, hundreds of thousands of hospitalizations and thousands or sometimes tens of thousands of deaths.

• CDC recommends annual flu vaccination for everyone 6 months and older.

• While flu vaccine can vary in how well it works, a flu vaccine is our best defense against getting the flu.

• Vaccination can reduce flu illnesses, doctors' visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations.

• Flu vaccine is designed to protect against the three or four flu viruses that research suggests will be most common during the upcoming season.

• It takes about two weeks after vaccination for protection to set in. Now is a good time to get vaccinated.

• Manufacturers report having shipped more than 145.4 million doses of flu vaccine as of January 8, 2016.

• Go to http://vaccine.healthmap.org/ or http://www.cdc.gov/flu to find a location near you where you can get vaccinated.

FluView Activity Update

Flu activity remains low across most of the country. In the latest FluView report, some key flu indicators increased slightly, while others fell. For example, the percentage of laboratory specimens testing positive for flu increased, however, reports of influenza-like-illness fell below the national baseline. It's likely that flu activity will increase again and that there are still weeks of influenza activity to come this season. Historically, flu most commonly peaks during the month of February. CDC recommends an annual flu vaccine for everyone 6 months of age and older. If you have not gotten vaccinated yet this season, you should get vaccinated now. Below is a summary of the key flu indicators for the week ending January 9, 2015:

• For the week ending January 9, the proportion of people seeing their health care provider (http://www.cdc.gov/flu/weekly/#S4) for influenza-like illness (ILI) is 2.0%, which is below the national baseline (2.1%). Four of 10 regions (Regions 1, 3, 4, and 6) reported ILI at or above their region-specific baseline levels. One way that CDC measures the length of the influenza season is the number of consecutive weeks during which ILI is at or above the national baseline.

• Puerto Rico and one state (South Carolina) experienced high ILI activity. New York City and seven states (Arizona, Connecticut, Illinois, Maryland, Pennsylvania, Texas, and Virginia) experienced low ILI activity. 42 states experienced minimal ILI activity. The District of Columbia did not have sufficient data to calculate an activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each state.

• No states reported widespread flu activity. Regional flu activity was reported by Guam, Puerto Rico, and nine states (Arizona, California, Connecticut, Iowa, Massachusetts, New Hampshire, North Carolina, Pennsylvania, and Virginia). Eleven states (Indiana, Kentucky, Maryland, Nevada, New Jersey, New Mexico, Oklahoma, Oregon, Texas, Utah, and Vermont) reported local influenza activity. The U.S. Virgin Islands and 28 states reported sporadic influenza activity. No influenza activity was reported by the District of Columbia and two states (Alabama and Tennessee). Geographic spread data show how many areas within a state or territory are seeing flu activity.

• Since October 1, 2015, 423 laboratory-confirmed influenza-associated hospitalizations have been reported through FluSurv-NET, a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations. This translates to a cumulative overall rate of 1.5 hospitalizations per 100,000 people in the United States. More data on hospitalization rates, including hospitalization rates during other influenza seasons, are available at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.

o The highest hospitalization rates are among people 65 and older (5.2 per 100,000), followed by children younger than 5 years (2.9 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.

o FluSurv-NET hospitalization data are collected from 13 states and represent approximately 8.5% of the total U.S. population. The number of hospitalizations reported does not reflect the actual total number of influenza-associated hospitalizations in the United States.

• The proportion of deaths(http://www.cdc.gov/flu/weekly/#S2) attributed to pneumonia and influenza (P&I) based on the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System is below system-specific epidemic thresholds.

• One influenza-associated pediatric death was reported to CDC during the week ending January 9. This death was associated with an influenza B virus and occurred during week 49 (the week ending December 12, 2015). A total of seven influenza-associated pediatric deaths have been reported during the 2015-2016 season.

• Nationally, the percentage of respiratory specimens(http://www.cdc.gov/flu/weekly/overview.htm#Viral) testing positive for influenza viruses in clinical laboratories during the week ending January 9 was 3.0%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories ranged from 0.6% to 5.4%.

o During the week ending January 9, of the 428 influenza-positive tests reported to CDC by clinical laboratories, 292 (68.2%) were influenza A viruses and 136 (31.8%) were influenza B viruses.

• The most frequently identified influenza virus type reported by public health laboratories during the week ending January 9 was influenza A viruses, with influenza A (H1N1)pdm09 viruses predominating.

o During the week ending January 9, 94 (83.9%) of the 112 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 18 (16.1%) were influenza B viruses. Of the 73 influenza A viruses that were subtyped, 15 (20.5%) were H3 viruses and 58 (79.5%) were A (H1N1)pdm09 viruses.

o Cumulatively from October 4, 2015-January 9, 2016, influenza A (H3) viruses were predominant in two of the four age groups ranging from 43.2% (ages 5-24 years) to 65.5% (ages 65 years and older). Influenza A (H1N1)pdm09 viruses were predominant in the 0-4 years age group (50.0%) and in the 25-64 years age group (50.0%).

• CDC has characterized 209 specimens (49 influenza A (H1N1)pdm09, 128 influenza A (H3N2) and 32 influenza B viruses) collected in the U.S. since October 1, 2015.

o All 49 (100%) influenza A (H1N1)pdm09 viruses were antigenically characterized as similar to A/California/7/2009, the influenza A (H1N1) component of the 2015-2016 Northern Hemisphere vaccine.

o All 128 H3N2 viruses were genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to cell-propagated A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015-2016 Northern Hemisphere vaccine.

 A subset of 78 H3N2 viruses also were antigenically characterized; 77 of 78 (98.7%) H3N2 viruses were similar to A/Switzerland/9715293/2013 by HI testing or neutralization testing.

o All 25 (100%) of the B/Yamagata-lineage viruses were antigenically characterized as similar to B/Phuket/3073/2013, which is included in both the 2015–16 Northern Hemisphere trivalent and quadrivalent vaccines.

o All seven (100%) of the B/Victoria-lineage viruses were antigenically characterized as similar to B/Brisbane/60/2008, which is included in the 2015-16 Northern Hemisphere quadrivalent vaccine.

• Since October 1, 2015, CDC has tested 75 influenza A (H1N1)pdm09, 166 influenza A (H3N2), and 64 influenza B viruses for resistance to the neuraminidase inhibitors antiviral drugs. While the vast majority of the viruses that have been tested are sensitive to oseltamivir, zanamivir, and peramivir, one influenza A (H1N1)pdm09 virus was reported during the week ending December 12 that showed resistance to oseltamivir and peramivir (but was sensitive to zanamivir).

FluView(http://www.cdc.gov/flu/weekly/fluactivitysurv.htm) is available – and past issues are archived(http://www.cdc.gov/flu/weekly/pastreports.htm) – on the CDC website.

Note: Delays in reporting may mean that data changes over time. The most up to date data for all weeks during the 2015-2016 season can be found on the current FluView(http://www.cdc.gov/flu/weekly/).

Influenza-Associated Pediatric Deaths

• One pediatric death was reported this week, bringing the total number of flu-associated deaths to seven for the 2015-2016 season.

• Because of confidentiality issues, CDC does not discuss or give details on individual cases.

• These deaths are a somber reminder of the danger flu poses to children.

• The single best way to protect against seasonal flu and its potential severe consequences in children is to get a seasonal flu vaccine each year.

• Vaccination is especially important for children younger than 5 years of age and children of any age with a long-term health condition like asthma, diabetes and heart disease and neurological and neurodevelopmental diseases. These children are at higher risk of serious flu complications if they get the flu.

• Yearly vaccination also is especially important for people in contact with high risk children in order to protect the child (or children) in their lives from the flu. In particular, children younger than 6 months are too young to be vaccinated themselves but are at high risk of flu complications if they get sick so the people around them should get vaccinated to protect the infant.

• Some children 6 months through 8 years of age require 2 doses of influenza vaccine. Children in this age group who are getting vaccinated for the first time will need two doses. Some children who have received influenza vaccine previously also will need two doses this season. A health care provider should be consulted to determine whether two doses are recommended for a child.

• Flu-related deaths in children younger than 18 years old should be reported through the Influenza-Associated Pediatric Mortality Surveillance System. The number of flu-associated deaths among children reported during the 2015-2016 flu season will be updated each week and can be found at http://www.cdc.gov/flu/weekly/#S3.

• Since 2004, when pediatric deaths associated with influenza infection became a nationally notifiable condition, the number of deaths reported to CDC each year has ranged from 37 (2011-2012 season) to 171 deaths (2012-2013 season).

• Last season, 148 influenza-associated pediatric deaths were reported to CDC.

Influenza-Associated Hospitalizations

• Laboratory-confirmed influenza-associated hospitalizations in children and adults in 13 states and more than 70 counties are monitored through the Influenza Hospitalization Surveillance Network (FluSurv-NET).

• The data are used to calculate a rate of laboratory-confirmed influenza-associated hospitalizations that is nationally representative and describes characteristics of person's hospitalized with severe flu illness.

o The rate describes the proportion of people during a given time period that were hospitalized and who tested positive for influenza during their hospital stay.

• Data regarding influenza-associated hospitalizations for the 2015-2016 influenza season is now available (week 1) in both FluView and FluView Interactive.

• 423 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2015.

• This translates to a cumulative overall rate of 1.5 hospitalizations per 100,000 people in the United States.

• The highest rate of hospitalization is among adults aged ≥65 years (5.2 per 100,000 population), followed by children aged 0-4 years (2.9 per 100,000 population. This is typical for seasonal influenza.

• Additional FluSurv-NET data can be found at: http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.