Weekly Virological Update on 14 July 2010
Virological Surveillance, week n° 26-2010 (27 June to 3 July 2010)
Trend of proportions of different type and subtype influenza viruses
Summary on week 26
- Overall influenza activity has remained at low levels in most parts of the world.
- In the Southern Hemisphere, increasing number of influenza A virus detections have been reported with co-circulation of pandemic A(H1N1) and seasonal A(H3N2) viruses.
- Influenza type B virus detections have decreased.
Global Virological Surveillance
Overall influenza activity has remained low with detection of 54.6% pandemic influenza A(H1N1) of influenza A viruses subtyped globally. Sporadic influenza A activity was reported in some countries, including Australia, Brazil, China and Singapore with co-circulation of pandemic A(H1N1) and A(H3N2) viruses. In Australia, the proportion of pandemic A(H1N1) (88.9 %) was significantly higher than seasonal A(H3N2) viruses (11.1%). Brazil reported sporadic pandemic A(H1N1) detections. Sporadic influenza B activity has been observed in some countries with decreased detections in China (56.9% of all influenza detections).
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 24 countries was 308. Of these, 181 (58.8%) were typed as influenza A and 127 (41.2%) as influenza B.
From the start of the pandemic in 19 April 2009 to 3 July 2010, the total number of specimens reported positive for influenza by NIC laboratories was 648,936*. Of these, 490,566 (75.6%) were pandemic A(H1N1), 8,946 (1.4%) were seasonal A(H1N1), 34,610 (5.3%) were A(H3N2), 80,839 (12.5%) were A (not subtyped) and 33,848(5.2%) were influenza B.
Pandemic virus characterization
19 April 2009 to 7th July 2010 - cumulatively 155 countries shared a total of 26, 466 specimens (20,128 clinical and 6,338 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, 298 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.