Pandemic (H1N1) 2009 - update 93
Weekly virological surveillance update
26 March 2010 - Overall influenza activity has continued to decrease in most part of the Northern Hemisphere. 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 influenza A viruses subtyped (100% in North America, El Salvador, Colombia and Cuba and 89.5% globally). Seasonal A(H1N1) viruses continue to be detected very sporadically in a couple of countries. Sporadic influenza A(H3N2) activity has been reported from some countries in recent weeks including Ghana and the Russian Federation. Influenza B, as in recent weeks, has been predominating subtype in China, Mongolia and the Islamic Republic of Iran, accounting for 81.6% of all influenza detections in China, 92.3% in Iran and 100% in Mongolia. Increased influenza B activity has also been observed in some European countries.
Based on FluNet reporting for the week from 7 to 13 March 2010, the total number of specimens reportedly positive for influenza viruses by National Influenza Centre (NIC) laboratories from 27 countries was 1,837. Of these, 414/1,837 (22.5%) were typed as influenza A and 1,423 (77.5%) as influenza B. Of all sub-typed influenza A viruses, 314/351 (89.5%) were pandemic A(H1N1) 2009.
From the start of the pandemic in 19 April 2009 to 13 March 2010, based on FluNet reporting by 83 countries, the total number of specimens reportedly positive for influenza viruses by NIC laboratories was 551,867 *. Of these, 428,362 (77.6%) were pandemic A(H1N1), 8,558 (1.6%) were seasonal A(H1N1), 30,578 (5.5%) were A(H3N2), 64,091 (11.6%) were A (not subtyped) and 20,194 (3.7%) were influenza B.
Since the beginning of the pandemic in 19 April 2009 to 20th March, 2010, cumulatively 154 countries shared a total of 24,612 specimens (18,813 clinical samples and 5,799 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. Click here 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.