Situation Update: Summary of Weekly FluView Report

Key Flu Indicators

According to this week’s FluView report, overall seasonal influenza activity is low across the United States. CDC recommends an annual flu vaccine for everyone 6 months of age and older. Getting vaccinated before flu activity begins is best. Below is a summary of the key flu indicators for the week ending October 24, 2015:

For the week ending October 24, the proportion of people seeing their health care provider for influenza-like illness (ILI) is 1.3% and remains below the national baseline (2.1%). All 10 U.S. regions reported ILI activity below region-specific baseline levels.
Puerto Rico experienced moderate ILI activity. New York City and all 50 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.
Guam and one state (Hawaii) reported regional influenza activity. Six states (Alabama, Iowa, Massachusetts, Oklahoma, Oregon and South Carolina) reported local influenza activity. Puerto Rico and 35 states reported sporadic influenza activity. The U.S. Virgin Islands, the District of Columbia, and 8 states reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
Influenza-associated hospitalization data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2015-2016 influenza season will be updated weekly starting later this season.
The proportion of deaths attributed to pneumonia and influenza (P&I) based on the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System is below their system-specific epidemic threshold.
At this time, no influenza-associated pediatric deaths have been reported for the 2015-2016 flu season. One influenza-associated pediatric death that occurred during the 2014-15 season was reported to CDC during the week ending October 24; and was associated with an influenza B virus. This death brings the total number of reported pediatric deaths occurring during that season to 147.
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending October 24 was 1.2%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories ranged from 0.4% to 2.7%.
The most frequently identified influenza virus type reported by public health laboratories during the week ending October 24 was influenza A viruses, with influenza A (H3) viruses predominating.
- During the week ending October 24, 33 (97.1%) of the 34 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 1 (2.9%) was an influenza B virus. Of the 26 influenza A viruses that were subtyped, 24 (72.7%) were H3 viruses and two (6.1%) were A (H1N1)pdm09 viruses.
No virus characterization data is available for specimens collected after October 1, 2015. However, CDC characterized 297 U.S. flu viruses during May 24–September 30, 2015, including 13 influenza A (H1N1)pdm09 viruses, 219 influenza A (H3N2) viruses, and 65 influenza B viruses. Virus characterization data will be updated weekly starting later in the season.
- All 13 influenza A (H1N1)pdm09 viruses were antigenically characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2015-2016 Northern Hemisphere.
- All 219 H3N2 viruses were genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015-2016 Northern Hemisphere vaccine.
- A subset of 95 H3N2 viruses also were antigenically characterized; 94 of 95 (99%) H3N2 viruses were A/Switzerland/9715293/2013-like by HI testing or neutralization testing.
- 38 (59%) of the 62 influenza B viruses collected and analyzed during this period belonged to the B/Yamagata lineage, and all were antigenically similar to the B/Phuket/3073/2013 virus, the influenza B component for both the 2015–16 Northern Hemisphere trivalent and quadrivalent vaccines.
- The remaining 27 (41%) influenza B viruses were antigenically characterized as B/Brisbane/60/2008-like, the recommended influenza B component of the 2015-16 Northern Hemisphere quadrivalent flu vaccine.
No antiviral resistance data is available for specimens collected after October 1, 2015. From May 24-September 30, CDC tested 272 U.S. flu viruses, including 8 influenza A (H1N1)pdm09, 198 influenza A (H3N2), and 66 influenza B viruses, for resistance to the neuraminidase inhibitors antiviral drugs. None of the tested viruses were found to be resistant to either oseltamivir, zanamivir, or peramivir. Antiviral resistance data will be updated weekly starting later in the season.

FluView is available – and past issues are archived – 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.