Weekly Virological Update on 28 July 2010
Virological Surveillance, week n° 28-2010 (11 July to 17 July 2010)
Trend of proportions of different type and subtype influenza viruses
Summary on week 28
- Overall influenza activity has remained at low levels in most parts of the world.
- Co-circulation of pandemic A(H1N1) and seasonal A(H3N2) viruses has been reported from some countries,.
- Influenza type B virus detections have decreased.
Global Virological Surveillance
Overall influenza activity has remained low. Globally 50.7% of the subtyped influenza A viruses were pandemic influenza A(H1N1) with circulation reported from Australia, Brazil, China, Japan, Mauritius, Madagascar and Singapore. Co-circulation of pandemic A(H1N1) and A(H3N2) viruses was reported from China and Singapore. Sporadic influenza B activity has been observed in some countries with decreased detections in China (45.1% of all influenza detections).
FluNet Report (For the week 11 July to 17 July 2010)
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 18 countries was 454. Of these, 279 (60.4%) were typed as influenza A and 180 (39.6%) as influenza B.
From the start of the pandemic in 19 April 2009 to 17 July 2010, the total number of specimens reported positive for influenza by NIC laboratories was 650,584*. Of these, 491,055 (75.5%) were pandemic A(H1N1), 8,959 (1.4%) were seasonal A(H1N1), 34,852 (5.4%) were A(H3N2), 81,020 (12.5%) were A (not subtyped) and 34,571 (5.3%) were influenza B.
Pandemic virus characterization
19 April 2009 to 25th July 2010 - cumulatively 155 countries shared a total of 26, 519 specimens (20,165 clinical and 6,354 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.