Pandemic (H1N1) 2009 - update 86
Weekly virological surveillance update
5 February 2010 - In nearly all countries where influenza infection in human is reported, the pandemic influenza A(H1N1) continues to be the predominant circulating influenza virus and the absolute predominant subtype among all influenza A viruses subtyped (100% in AMR, 95% in EUR and 93% global). Sporadic detections of seasonal A(H1N1), A(H3N2) and influenza B viruses were reported from a few countries in Africa, Middle east and East Europe. In China, influenza B activity continued increasing trend and accounted for 62.5% of all influenza detections.
A total of 25 countries reported to FluNet during the period 17th January 2010 to 23rd January 2010. Based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 2,354. Of these, 1267 / 2354 (54%) were typed as influenza A and 1,087 (46%) as influenza B. Of all sub-typed influenza A viruses, 93% (1,051/1,133) were pandemic A(H1N1) 2009.*
From the start of the pandemic in 19 April 2009 to 23 January 2010, based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 506,770. Of these, 399,218 (78.8%) were pandemic A(H1N1), 7,531 (1.5%) were seasonal A(H1N1), 28,582 (5.6%) were A(H3N2), 60,770 (12.0%) were A (not subtyped) and 10,596 (2.1%) were influenza B.
Since the beginning of the pandemic in 19 April 2009 to 30th January, 2010, cumulatively 153 countries shared a total of 23822 specimens (18400 clinical samples and 5422 virus isolates) with WHO CCs for further characterization. The absolute majority of pandemic A(H1N1) 2009 influenza viruses analysed to date were antigenically and genetically closely related to the vaccine virus A/California/7/2009. The pandemic A(H1N1) 2009 viruses with D222G substitution have also been seen antigenically indistinguishable to the A/California/7/2009 (H1N1) vaccine virus.
Antiviral susceptibility surveillance has been conducted by the WHO Global Influenza Surveillance Network (GISN) including WHO CCs. So far, pandemic A(H1N1) specimens and isolates from at least 90 countries have been tested, showing that oseltamivir resistant pandemic A(H1N1) viruses are sporadic with rare onward transmission. So far, 225 cases of oseltamivir resistance have been reported by GISN and other partners. All of these viruses showed the H275Y substitution 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.