Pandemic (H1N1) 2009 - update 88
Weekly virological surveillance update
19 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 human influenza infection is reported, the pandemic influenza A (H1N1) continues to be predominating subtype among all influenza A viruses subtyped (100% in AMR, 98% in EUR and 97% global). Seasonal A (H1N1) viruses continue to be detected very sporadically, mainly from Asia. Sporadic influenza A (H3N2) activity has been reported from some countries in recent weeks. Influenza B activity continued to increase in China, becoming the predominant virus circulating in the country accounting for 82 % of all influenza detections.
A total of 27 countries reported to FluNet during the period 31st January 2010 to 6thFebruary 2010. Based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 844. Of these, 785/ 844 (93.0%) were typed as influenza A and 59 (7.0%) as influenza B. Of all sub-typed influenza A viruses, 97% (651/673) were pandemic A(H1N1) 2009.* Hong Kong SAR China has reported increased influenza B activity in recent weeks and accounted for 34.5% of all influenza detections in the reporting week.
From the start of the pandemic in 19 April 2009 to 6th February 2010, based on FluNet reporting, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 529,380. Of these, 415,911 (78.6%) were pandemic A(H1N1), 8,228 (1.6%) were seasonal A(H1N1), 29,843 (5.6%) were A(H3N2), 62.528 (11.8%) were A (not subtyped) and 12,778 (2.4%) were influenza B. Cumulatively, the pandemic virus continued to be predominating subtype reported with detection of a very small proportion of seasonal strains.
Since the beginning of the pandemic in 19 April 2009 to 13thFebruary, 2010, cumulatively 153 countries shared a total of 24142 specimens (18627 clinical samples and 5515 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.
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, 248 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.