Pandemic (H1N1) 2009 - update 92
Weekly virological surveillance update
19 March 2010 - Pandemic influenza A (H1N1) 2009 circulating viruses 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 most countries where detection of human influenza virus was reported, the pandemic influenza A (H1N1) continues to be the predominating subtype among all influenza A viruses subtyped (100% in North America region and 90.2% globally). Seasonal A (H1N1) viruses continue to be detected very sporadically in only a few countries. Sporadic influenza A (H3N2) activity has also been reported from some countries. As in recent weeks, influenza B has been predominating subtype in China, Hong Kong China SAR, Iran, Mongolia, the Republic of Korea and the Russian Federation. Increased influenza B activity has also been observed in some European countries.
Based on FluNet reporting for the week from 28 February to 6 March 2010, the total number of specimens reportedly positive for influenza viruses by National Influenza Centre (NIC) laboratories from 28 countries was 1,542. Of these, 524/1,542 (34.0%) were typed as influenza A and 1,018 (66.0%) as influenza B. Of all sub-typed influenza A viruses, 90.2% (378/419) were pandemic A (H1N1) 2009.
From the start of the pandemic in 19 April 2009 to 6 March 2010, based on FluNet reporting by 83 countries, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 545,749 *. Of these, 425,650 (78.0%) were pandemic A (H1N1), 8,257 (1.6%) were seasonal A (H1N1), 30,464 (5.6%) were A (H3N2), 63,799 (11.7%) were A (not subtyped) and 15,237 (2.8%) were influenza B
Since the beginning of the pandemic in 19 April 2009 to 13th March, 2010, cumulatively 154 countries shared a total of 24,537 specimens (18,808 clinical samples and 5,729 virus isolates) with WHO CCs for further characterization. The majority of pandemic A (H1N1) 2009 influenza viruses analyzed to date are 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. The data showed that oseltamivir resistant pandemic A (H1N1) viruses are sporadically detected with rare onward transmission. So far, 267 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.