Pandemic (H1N1) 2009 - update 95
Weekly virological surveillance update
9 April 2010 - Overall influenza activity has remained at low level in most parts of the Northern Hemisphere. Little activity has been reported in the Southern Hemisphere in 2010 to date. In most countries where human infection of influenza virus was reported, the pandemic influenza A(H1N1) continues to be the predominating influenza A viruses subtyped (99.4% in Canada, Cuba and the United States and 89.8% globally).
Seasonal A(H1N1) viruses have been detected very sporadically in Russian Federation. Sporadic influenza A(H3N2) activity has been reported from some countries. Influenza B, as in recent weeks, has been predominating subtype accounting for 64.8% of all influenza detections in China, 65.1% in Russian Federation, 93.2% in Republic of Korea, and 100% in Mongolia. Increased sporadic influenza B activity has also been observed in some European countries.
Based on FluNet reporting for the week from 21 to 27 March 2010, the total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NIC) from 25 countries was 810. Of these, 303/610(37.4%) were typed as influenza A and 460(56.8%) as influenza B.
From the start of the pandemic in 19 April 2009 to 27 March 2010, based on FluNet reporting by 84 countries, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 603,031 *. Of these, 468,528(77.7%) were pandemic A(H1N1), 8,638 (1.4%) were seasonal A(H1N1), 30,745 (5.1%) were A(H3N2), 72,974 (12.1%) were A (not subtyped) and 22,054 (3.7%) were influenza B.
Since the beginning of the pandemic on 19 April 2009 to 3rd April 2010, cumulatively 155 countries shared a total of 24913 (19074 clinical and 5839 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 recommended 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, 278 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. (See below to obtain more information on oseltamivir resistant viruses).
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.