Weekly Virological Update on 05 August 2010
Virological Surveillance, week n° 29-2010 (18 July to 24 July 2010 2010)
Trend of proportions of different type and subtype influenza viruses
Summary on week 29
- Overall influenza activity has remained at low levels in most parts of the world.
- Co-circulation of pandemic A(H1N1), A(H3N2) and influenza B viruses has been reported from some countries,
- Influenza type B virus detections have decreased.
Global Virological Surveillance
Overall influenza activity has remained low. Globally 51.1% of the subtyped influenza A viruses were pandemic influenza A(H1N1) with circulation reported from Australia, China, Chile, Ghana, India, New Zealand and Thailand. Co-circulation of pandemic A(H1N1), A(H3N2) and influenza B viruses was reported from China, Chile and Thailand. Sporadic influenza B activity has been observed in some countries with decreased level of detections in China (34.9% of all influenza detections).
FluNet Report (For the week 18 July to 24 July 2010)
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 23 countries was 572. Of these, 389 (68%) were typed as influenza A and 183 (32%) as influenza B.
From the start of the pandemic in 19 April 2009 to 24 July 2010, the total number of specimens reported positive for influenza by NIC laboratories was 651,449*. Of these, 491,382 (75.4%) were pandemic A(H1N1), 8,960 (1.4%) were seasonal A(H1N1), 345,069 (5.4%) were A(H3N2), 81,070 (12.4%) were A (not subtyped) and 34,841 (5.3%) were influenza B.
Pandemic virus characterization
19 April 2009 to 1st August 2010 - cumulatively 155 countries shared a total of 26, 543 specimens (20,177 clinical and 6,366 isolates) with WHO CCs.
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.
So far, 302 cases associated with oseltamivir resistant pandemic A(H1N1) viruses 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.