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Overall, reporting of influenza remains subdued, although there are some signs of slight increases in influenza-like activity in the southern hemisphere.
Once again, seasonal H3N2 is part of the mix being reported in some countries, which means we may have two influenza A strains to contend with this fall.
The good news is, H3N2 is included in this fall’s seasonal flu shot, along with novel H1N1, and the B/Brisbane/60/2008-like virus.
The bad news is, since the new strain of H3N2 (A/Perth/16/2009) has drifted antigenically away from the previous strain, those who don’t get vaccinated may find themselves without much in the way of acquired immunity this fall.
First a look at this week’s Virological report from the World Health Organization, and then the CDC’s latest International Update.
Weekly Virological Update on 30 June 2010
Virological Surveillance, week no. 24 (13 to 19 June 2010)
Summary on week 24
- 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 co-circulation of A(H1N1)2009 pandemic virus and seasonal A(H3N2).
Global Virological Surveillance
Influenza B viruses continued to be predominating in some countries and areas of Northern Hemisphere, including China (69.7% of all influenza detections) and Russian Federation (86.7%). 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, Chile and South Africa. The proportion of A(H3N2) increased in Australia and South Africa while A(H1N1)2009 pandemic virus was reported as predominant virus in Brazil and Chile.
FluNet Report
The total number of specimens reportedly positive for influenza viruses by National Influenza Centres (NICs) from 20 countries was 218. Of these, 117 (53.7%) were typed as influenza A and 101 (46.3%) as influenza B.
From the start of the pandemic in 19 April 2009 to 19 June 2010, the total number of specimens reported positive for influenza by NIC laboratories was 644,883*. Of these, 489,229 (75.9%) were pandemic A(H1N1), 8,923 (1.4%) were seasonal A(H1N1), 32,897 (5.1%) were A(H3N2), 80,669(12.5%) were A (not subtyped) and 33,046(5.1%) were influenza B.
From the CDC we get this International update for week 23 to 24. As you can see, H3N2 continues to circulate in Singapore, South Africa, and Chile.
2009 H1N1 continues to actively circulate in certain areas of the tropics, including the Caribbean, West Africa, and South and Southeast Asia. In the Southern Hemisphere, influenza A (H3N2) viruses are currently co-circulating with 2009 H1N1. In the Northern Hemisphere, the number of influenza B viruses detected has exceeded reports of influenza A.
Influenza A (H3N2) activity is currently increasing in Nicaragua and circulating at low levels in South Africa, Australia, East Africa, and South America. Low levels of 2009 H1N1 influenza activity have been reported from Chile and Argentina. 2009 H1N1 activity continues to increase in Southern regions of India and is circulating at low levels in several countries in Southeast Asia. Influenza type B continues to actively circulate in Central and Southern regions of Africa and is currently co-circulating with 2009 H1N1 in Bangladesh.
Selected Highlights
- According to WHO, the majority of 2009 H1N1 virus isolates tested worldwide remains sensitive to oseltamivir, an antiviral medicine used to treat flu. Among 2009 H1N1 isolates tested worldwide, 298 have been found to be resistant to oseltamivir – as of May 28, 2010, 67 of these isolates were detected in the United States. Approximately 1% of U.S. 2009 H1N1 viruses tested by CDC since September 1, 2009, have been resistant to oseltamivir.
- Influenza B continues to predominate in many countries of the Northern Hemisphere, including China (69.7% of all influenza detections) and the Russian Federation (86.7%).
- The proportion of influenza A (H3N2) detections increased in Australia and South Africa, while 2009 H1N1 is circulating as the predominant virus in Brazil and Chile. On February 18, 2010, WHO published recommendations for the following viruses to be used for influenza vaccines in the 2010-2011 influenza season of the Northern Hemisphere:
- an A/California/7/2009 (H1N1)-like virus;
- an A/Perth/16/2009 (H3N2)-like virus*;
- a B/Brisbane/60/2008-like virus.
* A/Wisconsin/15/2009 is an A/Perth/16/2009 (H3N2)-like virus and is a 2010 Southern Hemisphere vaccine virus.
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