Pandemic (H1N1) 2009 - update 87
Weekly virological surveillance update
12 February 2010 - Pandemic influenza A (H1N1) 2009 infections have continued to decrease in most countries of the Northern Hemisphere in recent weeks. Little activity has been reported in the Southern Hemisphere in 2010 to date. In nearly all countries where influenza infection is reported, the pandemic influenza A (H1N1) continues to be predominating among all influenza A viruses subtyped (100% in AMR, 98% in EUR and 94% global). Sporadic detections of seasonal A (H1N1), A (H3N2) and influenza B viruses were reported from a few countries in Africa, Europe and the Middle East region. China continued to report increased influenza B activity.
A total of 27 countries reported to FluNet during the period 24th January 2010 to 30thJanuary 2010. Based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 2,012. Of these, 922 / 2,012 (45.8%) were typed as influenza A and 1,090 (54.2%) as influenza B. Of all sub-typed influenza A viruses, 94% (730 / 775) were pandemic A(H1N1) 2009.* In China, influenza B activity continued the increasing trend in 2010 and accounted for 72.2% of all influenza detections in the reporting week.
The trend of proportions of different type and subtype influenza viruses infecting human (.pdf)
From the start of the pandemic in 19 April 2009 to 30th January 2010, based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 519,011. Of these, 407,168 (78.5%) were pandemic A(H1N1), 8,177 (1.6%) were seasonal A(H1N1), 29,601 (5.7%) were A(H3N2), 61,793 (11.9%) were A (not subtyped) and 12,190 (2.3%) were influenza B. Cumulatively, the pandemic virus continued to be the predominant subtype reported with a very small proportion of seasonal strains detected.
Since the beginning of the pandemic in 19 April 2009 to 6thFebruary, 2010, cumulatively 153 countries shared a total of 24005 specimens (18557 clinical samples and 5448 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 91 countries have been tested, showing that oseltamivir resistant pandemic A (H1N1) viruses are sporadic with rare onward transmission. So far, 245 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.