Pandemic (H1N1) 2009 - update 101
Weekly virological surveillance update
21 May 2010 - Overall influenza activity has remained at low levels in most parts of the world. 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 globally (80.9%).
Seasonal A(H1N1) viruses were detected sporadically in China and the Russian Federation. Sporadic influenza A(H3N2) activity was reported from some countries including China, Ghana, Kenya and Thailand. Influenza B was reported as the predominating influenza virus accounting for 89.6% of all influenza detections in Russian Federation, 90.8% in China, 90.9% in Republic of Korea and 100% in Cameroon and Islamic Republic of Iran. Increased sporadic influenza B activity has also been observed in some other countries.
Based on FluNet reporting for the week from 2 to 8 May 2010, the total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 28 countries was 696. Of these, 150 (22%) were typed as influenza A and 546 (78%) as influenza B.
From the start of the pandemic in 19 April 2009 to 8 May 2010, based on FluNet reporting by 88 countries, the total number of specimens reported positive for influenza by NIC laboratories was 634,896*. Of these, 482,693 (76.0%) were pandemic A(H1N1), 8,864 (1.4%) were seasonal A(H1N1), 32,453 (5.1%) were A(H3N2), 80,169 (12.6%) were A (not subtyped) and 30,615 (4.8%) were influenza B
Since the beginning of the pandemic on 19 April 2009 to 15th May 2010, cumulatively 155 countries shared a total of 25,546 specimens (19,573 clinical and 5,973 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 92 countries have been tested. The data showed that oseltamivir resistant pandemic A(H1N1) viruses are sporadically detected with rare onward transmission. So far, 289 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.