CDC REPORTS LOW LEVEL OF ACTIVITY IN THE FIRST TWO MONTHS OF THE 2006-07 U.S. INFLUENZA SEASON

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January 2, 2007CDC REPORTS LOW LEVEL OF ACTIVITY IN THE FIRST TWO MONTHS OF THE 2006-07 U.S. INFLUENZA SEASONCDC published "Update: Influenza Activity-United States, October 1-December 9, 2006" in the December 22, 2006, issue of MMWR. Portions of the article are reprinted below.***********************During October 1-December 9, 2006, influenza activity remained low in the United States overall but increased in southeastern states. This report summarizes U.S. influenza activity since October 1, the beginning of the 2006-07 influenza season, and updates the previous summary. Viral Surveillance During October 1-December 9, 2006, the World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System collaborating laboratories in the United States tested 27,474 specimens for influenza viruses, and 884 (3.2%) were positive. Of these, 689 (77.9%) were influenza A viruses and 195 (22.1%) were influenza B viruses. A total of 171 (24.8%) of the 689 influenza A viruses were subtyped; 162 (94.7%) of these were influenza A (H1) viruses, and nine (5.3%) were influenza A (H3) viruses. Influenza-positive tests were reported from 37 states in all nine surveillance regions; 441 (49.9%) of the 884 positive tests were reported from Florida. Antigenic Characterization States are requested to submit a subset of their influenza isolates to CDC for further antigenic characterization. Since October 1, 2006, CDC has antigenically characterized 28 influenza viruses collected and submitted by U.S. laboratories, including 10 influenza A (H1) isolates from six states, one influenza A (H3) isolate, and 17 influenza B viruses from four states. Eight of the 10 influenza A (H1) viruses were characterized as A/New Caledonia/20/99-like, the influenza A (H1) component of the 2006-07 influenza vaccine, and two showed reduced titers with ferret antisera produced against A/New Caledonia/20/99. The influenza A (H3) virus was characterized as A/Wisconsin/67/2005-like, the influenza A (H3) component of the 2006-07 influenza vaccine. Influenza B viruses currently circulating can be divided into two antigenically distinct lineages represented by B//02/87 and B/Yamagata/16/88. The influenza B component of the 2006-07 influenza vaccine is B/Ohio/01/2005, which belongs to the B/ lineage of viruses. Six (35.3%) of the 17 influenza B viruses characterized belong to the B/ lineage of viruses; three were similar to B/Ohio/01/2005, and three had reduced titers with antisera produced against B/Ohio/01/2005. Eleven (64.7%) of the 17 influenza B viruses characterized belong to the B/Yamagata lineage of viruses. Nine (81.8%) of the 11 influenza B/Yamagata viruses were received from a single state. . . .Editorial Note:During October 1-December 9, 2006, the United States experienced a low level of influenza activity. Widespread and regional activity was reported in only six states in the southeastern area of the country. Outbreaks were reported primarily among children in Alabama, Florida, and North Carolina. Influenza virus isolates have been reported in all nine surveillance regions in the United States. Patient visits for ILI [influenza-like illness], represented by the Sentinel Provider Surveillance Network, and P & I [pneumonia and influenza] mortality, represented by the 122 Cities Mortality Reporting System, have not exceeded national baseline levels. In addition, no influenza-associated hospitalizations from the EIP [Emerging Infections Program] or NVSN [New Vaccine Surveillance Network] surveillance systems have been reported to CDC and no influenza-related pediatric deaths have been reported through the National Notifiable Diseases Surveillance System. Vaccination is the best method for prevention of influenza and its potentially severe complications. Although the optimal months for influenza vaccination are October and November, vaccination in December and beyond is recommended because influenza activity peaks in January or later during most seasons. The degree of antigenic match between the current vaccine strains and strains that will circulate this season will be determined as more strains become available for analysis. To date, influenza A (H1) viruses have been reported most frequently, and the majority of influenza A (H1) viruses characterized are well matched by the vaccine. Influenza vaccine can be administered to any person who wants to reduce the likelihood of becoming ill with influenza. Annual influenza vaccination is particularly targeted toward persons at increased risk for influenza-related complications and severe disease (e.g., children aged 6-59 months, pregnant women, persons aged >=50 years, and persons aged 6 months-49 years with certain chronic medical conditions) and their close contacts (e.g., healthcare workers and household contacts of persons at increased risk, including contacts of children aged <6 months). In addition, all children aged 6 months to <9 years who have not been previously vaccinated at any time should receive 2 doses of influenza vaccine. Vaccine should be offered throughout the influenza season, even after influenza activity has been documented in the community. Influenza surveillance reports for the United States are posted online weekly during October-May and are available at http://www.cdc.gov/flu/weekly/fluactivity.htm Additional information regarding influenza viruses, influenza surveillance, the influenza vaccine, and avian influenza is available at http://www.cdc.gov/flu ***********************To access a web-text (HTML) version of the complete article, go to: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5550a5.htmTo access a ready-to-print (PDF) version of this issue of MMWR, go to: http://www.cdc.gov/mmwr/PDF/wk/mm5550.pdf