INFLUENZA (31): CENTERS FOR DISEASE CONTROL AND PREVENTION UPDATE
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International Society for Infectious Diseaseshttp://www.isid.org
Date: Fri 18 May 2012
Source: Flu View, Centers for Disease Control and Prevention (CDC), Flu Activity and Surveillance [abridged, edited]http://www.cdc.gov/flu/weekly/
2011-2012 Influenza Season Week 19 ending 12 May 2012
During week 19 (6-12 May 2012), influenza activity declined nationally and in most regions, but remained elevated in some areas of the United States.
- U.S. Virologic Surveillance: Of the 2171 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 288 (13.3 percent) were positive for influenza.
- Pneumonia and Influenza (P&I) Mortality Surveillance: The proportion of deaths attributed to P&I was below the epidemic threshold.
- Influenza-associated Pediatric Mortality: 2 influenza-associated pediatric deaths were reported. One was associated with an influenza B virus and one was associated with an influenza A virus for which the subtype was not determined.
- Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.2 percent, which is below the national baseline of 2.4 percent. All regions reported ILI below region-specific baseline levels. 2 states experienced low ILI activity; New York City and 47 states experienced minimal ILI activity, and the District of Columbia and one state had insufficient data to calculate ILI activity.
- Geographic Spread of Influenza: One state reported widespread geographic activity; 5 states reported regional influenza activity; 11 states reported local activity; the District of Columbia, Guam, Puerto Rico, and 30 states reported sporadic activity, and the U.S. Virgin Islands and 3 states reported no influenza activity.
U.S. Virologic Surveillance
WHO and NREVSS collaborating laboratories located in all 50 states report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza type and subtype. The results of tests performed during the current week:
Number of specimens tested 2171.
Number of positive specimens 288 (13.3 percent)Positive specimens by type/subtype
- Influenza A 152 (52.8 percent),
2009 H1N1 12 (7.9 percent)
Subtyping not performed 79 (52.0 percent)
(H3)61 (40.1 percent)
- Influenza B136 (47.2 percent)
Predominant influenza viruses can vary by region and even between states within the same region. Seasonal influenza A (H3) viruses have predominated since the start of the 2011-2012 season nationally and in most regions, however 2009 H1N1 and influenza B viruses continue to circulate. The timing of influenza activity also can vary by region. While influenza activity may have peaked and be declining in some states or regions, other areas may not yet have reached their peak activity level. Region specific data can be found at http://gis.cdc.gov/grasp/fluview/flupor ... board.html
Influenza viruses circulate year-round and substantial activity may persist as late as May.
CDC has antigenically characterized 1514 influenza viruses [369 2009 H1N1 viruses, 893 influenza A (H3N2) viruses, and 252 influenza B viruses] collected by U.S. laboratories since 1 Oct 2011.
2009 H1N1 :
- 363 (98.4 percent) of the 369 viruses were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2011-2012 influenza vaccine for the Northern Hemisphere.
- 6 viruses (1.6 percent) tested showed reduced titers with antiserum produced against A/California/7/2009.
Influenza A (H3N2) :
- 723 (81.0 percent) of the 893 viruses were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2011-2012 influenza vaccine for the Northern Hemisphere.
- 170 viruses (19.0 percent) tested showed reduced titers with antiserum produced against A/Perth/16/2009.
Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) :
- Victoria Lineage : 117 (46.4 percent) of the 252 influenza B viruses tested belong to the B/Victoria lineage of viruses.
- 110 (94.0 percent) of these 117 viruses were characterized as B/Brisbane/60/2008-like, the influenza B component of the 2011-2012 Northern Hemisphere influenza vaccine.
- 7 (6.0 percent) of these 117 viruses showed reduced titers with antisera produced against B/Brisbane/60/2008.
- Yamagata Lineage : 135 (53.6 percent) of the 252 influenza B viruses tested belong to the B/Yamagata lineage of viruses.
While less than 50 percent of U.S. influenza B viruses tested this season are similar to the influenza B component in the 2011-2012 influenza vaccine, influenza B viruses account for only 13 percent of influenza positive tests reported to CDC this season. Worldwide, the majority of influenza B viruses circulating have been similar to the influenza B component of the 2011-2012 Northern Hemisphere influenza vaccine.
Composition of the 2012-2013 Influenza Vaccine
The World Health Organization (WHO) has recommended vaccine viruses for the 2012-2013 Northern Hemisphere influenza vaccines, and FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) has made recommendations for the composition of the 2012-2013 U.S. influenza vaccines. Both agencies recommend that the vaccine contain A/California/7/2009-like (2009 H1N1), A/Victoria/361/2011-like (H3N2), and B/Wisconsin/1/2010-like (B/Yamagata lineage) viruses.
This recommendation changes the influenza A (H3N2) and influenza B virus components of the 2011-2012 Northern Hemisphere vaccine formulation. This recommendation was based on global influenza virus surveillance data related to epidemiology and antigenic characteristics, serological responses to 2011-2012 trivalent seasonal vaccines, and the availability of candidate strains and reagents.
Testing of 2009 H1N1, influenza A (H3N2), and influenza B virus isolates for resistance to the neuraminidase inhibitors (oseltamivir and zanamivir) is performed at the CDC using a functional assay. Additional 2009 H1N1 clinical samples are tested for a single mutation in the neuraminidase of the virus known to confer oseltamivir resistance (H275Y).
High levels of resistance to the adamantanes (amantadine and rimantadine) persist among 2009 H1N1 and A (H3N2) viruses (the adamantanes do not have activity against influenza B viruses).
So far this season, 16 oseltamivir-resistant 2009 H1N1 viruses have been detected nationally. 3 patients were using oseltamivir for one day or more at the time of specimen collection. 13 had no exposure to oseltamivir; out of those 13 patients, 2 had family members using oseltamivir. (Resistance of influenza A viruses to antiviral drugs can occur spontaneously or emerge during the course of antiviral treatment or antiviral exposure).
11 of the 16 oseltamivir-resistant viruses were collected from January to April 2012 and are from Texas, where a total of 423 2009 H1N1 specimens have been tested for oseltamivir resistance. Oseltamivir resistance remains quite low nationally and in Texas, even though the percentage of oseltamivir-resistant 2009 H1N1 viruses in Texas (2.6 percent) is higher than the national percentage. The CDC continues to recommend the use of oseltamivir or zanamivir as early as possible for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at greater risk for influenza-related complications. Use of the adamantanes is not recommended.
Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at http://www.cdc.gov/flu/antivirals/index.htm
[Of particular note is the recommendation, endorsed by the WHO, concerning the need to amend the composition of the 2012-2013 Northern Hemisphere influenza vaccine in response to the epidemiology, antigenic characteristics, and serological responses to 2011-2012 trivalent seasonal vaccine.
The appearance of neuraminidase inhibitor resistant virus in North America contrasts with its absence in Europe and elsewhere (http://www.euroflu.org/cgi-files/bulletin_v2.cgi
). This may reflect no more than differences in clinical practise. - Mod.CP]
[We are entering the flu season in the Southern Hemisphere, and would like to know as soon as possible how good the match of the Southern Hemisphere vaccine is to what is circulating here. The last 2 WHO updates (see refs. below) have not been informative about that.
In Rio de Janeiro free vaccination is being offered to anyone over 65 years between 5-25 May. - Mod.JW]
Influenza (37): WHO update 20120512.1131168
Influenza (30): WHO update 20120413.1100438
Influenza (29): H3N2v cross-reactive antibodies 20120412.1099325
Influenza (28): USA (UT) H3N2v isolation 20120412.1098447
Influenza (27): USA (WA) surveillance 20120411.1097741
Influenza (26): H3N2 surveillance Canada (BC), USA 20120408.1093983
Influenza (25): H3N2v, pathogenesis & transmission 20120407.1093271
Influenza (24): USA (Pacific NW) 20120406.1092588
Influenza (23): surveillance policy 20120404.1090248
Influenza (22): surveillance policy 20120402.1086648
Influenza (21): update 20120330.1085988]