Pandemic (H1N1) 2009 - update 84
Weekly virological surveillance update
22 January 2010 - Pandemic influenza A(H1N1) 2009 viruses persist in many countries around the world although most Northern Hemisphere countries have seen decreasing activity in the last few weeks. The pandemic virus continues to be the predominant circulating influenza virus in all countries where influenza is reported.
Sporadic detections of seasonal A(H1N1), A(H3N2) and influenza B viruses were reported from a few countries. The majority of seasonal influenza detections were reported by China where increased influenza B detections were observed relative to previous weeks.
For this reporting week (3rd January 2010 to 9th January 2010); a total of 24 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 2,771. Of these, 2067 (74.6%) were typed as influenza A and 505 (18.2%) as influenza B. Of all sub-typed influenza A viruses, 97.2% (2,010/2067) were pandemic (H1N1) 2009. The above numbers represent only the specimens and results reported to FluNet.
Since the beginning of the pandemic in 19 April 2009 to 16th January,2010, cumulatively 153 countries shared a total of 23,527 specimens (18,299 clinical samples and 5,228 virus isolates) with WHO CCs for further analysis. All pandemic A(H1N1) 2009 influenza viruses analysed to date appear to be antigenically and genetically closely related to the vaccine virus A/California/7/2009. The pandemic (H1N1) 2009 viruses with D222G substitution have also been seen antigenically indistinguishable to the A/California/7/2009 (H1N1) vaccine virus.
Most of seasonal A(H1N1) viruses tested were antigenically and genetically closely related to the A/Brisbane/59/2007 vaccine virus. Seasonal A(H3N2) viruses were mostly antigenically and genetically closely related to A/Perth/16/2009 -like viruses (WHO recommended virus for 2010 Southern Hemisphere vaccine). Influenza B viruses were predominantly of the B/Victoria-lineage and the majority were antigenically and genetically closely related to the vaccine virus B/Brisbane/60/2008. (WHO recommended virus for 2010 Southern Hemisphere vaccine).
The WHO Global Influenza Surveillance Network (GISN) including WHOCCs conducts systematic surveillance for antiviral susceptibility. So far, antiviral susceptibility testing conducted by WHO CCs and other GISN laboratories on pandemic A (H1N1) specimens and isolates from at least 87 countries indicates that oseltamivir resistant pandemic H1N1 viruses are sporadic detections with rare onward transmission. So far, 206 cases of oseltamivir resistance have been reported by GISN and other WHO partners. All of these viruses showed the H275Y mutation and all remain sensitive to zanamivir.
WHO, through the GISN, continues monitoring the evolution and global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect humans.
*Some NICs report data to FluNet retrospectively and updates of previous data with new results are frequent.