Guest Post: Flu Activity

By: Donna Lazorik, RN, MS
Deputy Program Manager for Program Development, Immunization Program
Massachusetts Dept. Public Health

National Flu Activity

Flu activity continues to increase in the U.S., according to CDC’s latest FluView report.  “Reports of influenza-like-illness (ILI) are nearing what have been peak levels during moderately severe seasons,” according to Dr. Joe Bresee, Chief of the Epidemiology and Prevention Branch in CDC’s Influenza Division.  “Anyone who has not already been vaccinated should do so now,”

While the timing of flu seasons is impossible to predict, based on past experience it’s likely that flu activity will continue for some time.  During the past 10 seasons, ILI remained at or above baseline for an average of 12 consecutive weeks.  One factor that may indicate increased severity this season is that the predominant circulating type of influenza virus is influenza A (H3N2) viruses, which account for about 76% of the viruses reported.  Bresee explains “typically ‘H3N2 seasons’ have been more severe, with higher numbers of hospitalizations and deaths, but we will have to see how the season plays out.”

So far this season, 91% of the influenza viruses that have been analyzed at CDC are like the viruses included in the 2012-2013 flu vaccine.  “While vaccination offers the best protection we have against influenza, it’s still possible that some people may become ill despite being vaccinated,” says Bresee.  (For information about why people may become sick with flu after vaccination, see 2012-2013 season Questions and Answers.)

CDC has recommendations on the use of antiviral medications to treat influenza.  Antiviral treatment, started as early as possible after becoming ill, is recommended for anyone with confirmed or suspected influenza who are hospitalized, seriously ill, or ill and at high risk of serious influenza-related complications, including young children, people 65 and older, people with certain underlying medical conditions and pregnant women.  Treatment should begin as soon as influenza is suspected, regardless of vaccination status or rapid test results and should not be delayed for confirmatory testing.

During December 23-29, Influenza Activity Increased in the U.S.

  • Outpatient Illness Surveillance:  Nationwide during week 52, 5.6% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI).  This percentage is above the national baseline of 2.2%.  This increase may be attributed in part to a reduced number of routine health care visits during the Christmas holidays, which has been observed in previous seasons. (ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)
  • Influenza-Associated Hospitalizations: The most commonly reported underlying medical conditions among hospitalized adults were metabolic conditions, cardiovascular disease, obesity, and chronic lung disease (excluding asthma).  Among 36 hospitalized women of childbearing age (15-44 years), seven were pregnant.  The most commonly reported underlying medical conditions in hospitalized children were asthma, neurologic disorders, and immune suppression.  Approximately 40% of hospitalized children had no identified underlying medical conditions.  Additional FluSurv-NET data can be found here.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
  • Influenza-Associated Pediatric Deaths: Two influenza-associated pediatric deaths were reported and were associated with influenza B viruses.  This brings the total number of influenza-associated pediatric deaths reported during the 2012-2013 season to 18.  Additional data can be found here.
  • For more information on national flu activity, visit

Antigenic Characterization:

CDC has antigenically characterized 413 influenza viruses [17 2009 H1N1 viruses, 281 influenza A (H3N2) viruses, and 115 influenza B viruses] collected by U.S. laboratories since October 1, 2012.

  • 2009 H1N1 [17]:
    • All 17 2009 H1N1 viruses tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2012-2013 influenza vaccine for the Northern Hemisphere.
  • Influenza A (H3N2) [281]:
    • 279 (99.3%) of the 281 H3N2 influenza viruses tested have been characterized as A/Victoria/361/2011-like, the influenza A (H3N2) component of the 2012-2013 Northern Hemisphere influenza vaccine.
    • 2 (0.7%) of the 281 H3N2 viruses tested showed reduced titers with antiserum produced against A/Victoria/361/2011.
  • Influenza B (B/Yamagata/16/88 and B/Victoria/02/87 lineages) [115]:
    • Yamagata Lineage [79]: 79 (68.7%) of the 115 influenza B viruses tested so far this season have been characterized as B/Wisconsin/1/2010-like, the influenza B component of the 2012-2013 Northern Hemisphere influenza vaccine.
    • Victoria Lineage [36]: 36 (31.3%) of 115 influenza B viruses tested have been from the B/Victoria lineage of viruses. 

Massachusetts Flu Activity

  • As of the week ending December 29, flu activity in Massachusetts continued to increase dramatically and is much higher than what is typically seen at this time of year.
Percentage of out-patient visits that is due to ILI*
as reported by Massachusetts sentinel provider sites

*Influenza-like illness (ILI, defined by fever >100F and cough and/or sore throat).

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Reminder: free brochures, pamphlets and posters are available to support your flu vaccination efforts and to inform the public on how to care for people with ILI.  Many of these materials are available in multiple languages.  Please see the attached form or go to the Massachusetts Health Promotion Clearing House to order these free materials.

Many free handwashing materials, including posters, flyers, sample newsletter articles, etc., are available at

CDC has a number of materials for free download, as well as web tools, at

Author: Tom Meyer

Tom Meyer is the Alliance's Membership Coordinator and Webmaster. His email address is

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