Weekly virological update: 23 June 2010
Virological Surveillance, week 23 (6 to 12 June 2010)
Trend of proportions of different type and subtype influenza viruses
Summary on week 23
- Overall influenza activity has remained at low levels in most parts of the world.
- In Northern Hemisphere the number of influenza type B virus detections exceeded that of influenza A.
- However, the detection of influenza A increased in South Hemisphere with the proportion of A(H3N2) increasing and exceeding that of the pandemic A(H1N1)
Global Virological Surveillance
Influenza B viruses continued to be predominating in some countries and areas of Northern Hemisphere, including China (69.8% of all influenza detections), 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 AFRO region, including Cameroon, Kenya and Madagascar, with the proportion of A(H3N2) increasing (15%).
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 23 countries was 288. Of these, 88 (30.6%) were typed as influenza A and 200 (69.4%) as influenza B.
From the start of the pandemic in 19 April 2009 to 12 June 2010, the total number of specimens reported positive for influenza by NIC laboratories was 643,702*. Of these, 488,740 (75.9%) were pandemic A(H1N1), 8,915 (1.4%) were seasonal A(H1N1), 32,630 (5.1%) were A(H3N2), 80,620(12.5%) were A (not subtyped) and 32,678(5.1%) 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 below to obtain more information on oseltamivir resistant viruses)
19 April 2009 to 20th June 2010 - cumulatively 155 countries shared a total of 26,105 specimens (19,866 clinical and 6,239 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.