Weekly Virological Update on 7 July 2010
Virological Surveillance, week n° 25-2010 (20 to 26 June 2010)
Trend of proportions of different type and subtype influenza viruses
Summary on week 25
- Overall influenza activity has remained at low levels in most parts of the world.
- In the Northern Hemisphere the number of influenza type B virus detections exceeded that of influenza A.
- In the Southern Hemisphere, there is an observation of increasing number of influenza A virus detections with co-circulation of pandemic A(H1N1) and seasonal A(H3N2) viruses.
Global Virological Surveillance
At low levels, influenza B viruses continued to be predominating in some countries and areas of Northern Hemisphere, including China (69.3% of all influenza detections) and Russian Federation (93.7%). Sporadic influenza B activity has also been observed in some other countries.
Sporadic influenza A activity was reported in some countries in the Southern Hemisphere, including Australia, Brazil and South Africa. The proportion of A(H3N2) increased in South Africa (53% of all detections) while pandemic A(H1N1) virus was reported as predominant in Brazil (93.8%). In Australia the proportion of co-circulation of pandemic A(H1N1) and seasonal A(H3N2) viruses is very similar (58.3% and 41.7% of all detection, respectively).
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 29 countries was 356. Of these, 194 (54.5%) were typed as influenza A and 162 (45.5%) as influenza B.
From the start of the pandemic in 19 April 2009 to 26 June 2010, the total number of specimens reported positive for influenza by NIC laboratories was 647,378*. Of these, 490,415 (75.8%) were pandemic A(H1N1), 8,946 (1.4%) were seasonal A(H1N1), 33,509 (5.2%) were A(H3N2), 80,737(12.5%) were A (not subtyped) and 33,645(5.2%) were influenza B.
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. Click here to obtain more information on oseltamivir resistant viruses.
19 April 2009 to 7th July 2010 - cumulatively 155 countries shared a total of 26, 437 specimens (20,128 clinical and 6,309 isolates) with WHO CCs.
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.