Pandemic (H1N1) 2009 - update 103
Weekly virological surveillance update
4 June 2010 - Overall influenza activity has remained at low levels in most parts of the world.
While in most countries where human infection of influenza virus was reported, among influenza A viruses subtyped, the pandemic influenza A(H1N1) continues to be predominant(78.1% globally), in several countries in Africa, however, the proportion of A(H3N2) virus detections has increased and exceeded that of pandemic A(H1N1).
Seasonal A(H1N1) viruses were detected sporadically in the Russian Federation. Sporadic influenza A(H3N2) activity was reported from some parts of Africa, and some countries including Australia and Russian Federation. Influenza B was reported as the predominating influenza virus accounting for 80.7% of all influenza detections in Hong Kong SAR of China and 89.7% in Russian Federation. Sporadic influenza B activity has also been observed in some other countries.
Based on FluNet reporting for the week from 16 to 22 May 2010, the total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 29 countries was 219. Of these, 74 (34%) were typed as influenza A and 145 (66%) as influenza B.
From the start of the pandemic in 19 April 2009 to 22 May 2010, based on FluNet reporting by 88 countries, the total number of specimens reported positive for influenza by NIC laboratories was 637,613*. Of these, 484,378 (76.0%) were pandemic A(H1N1), 8,874 (1.4%) were seasonal A(H1N1), 32,501 (5.1%) were A(H3N2), 80,441(12.6%) were A (not subtyped) and 31,317 (4.9%) were influenza B.
Since the beginning of the pandemic on 19 April 2009 to 29th May 2010, cumulatively 156 countries shared a total of 25,752 specimens (19,728 clinical and 6024 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, 292 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.