WHO : Influenza update number 154

The latest influenza update from WHO, excerpt :

" Summary

• Influenza activity in the temperate regions of the northern hemisphere is low but increasing in North America and most of Europe. A few countries of southern Europe appear to have now peaked along with the countries of northern Africa and the Middle East.

•Countries in the tropical zone reported low levels of influenza activity.

• Influenza activity in the temperate countries of the southern hemisphere is at inter-seasonal levels.

• The most commonly detected virus type or subtype throughout the northern hemisphere temperate zone has been influenza A(H3N2). Mexico is the exception, where influenza A(H1N1)pdm09 is the predominant subtype circulating and China and the surrounding countries where influenza type B is predominant. Influenza type B has been increasing in recent weeks in Canada as well.

• Oseltamivir resistance has not increased notably over levels reported in previous seasons.

• While most of the viruses characterized early this season were antigenically related viruses in the current trivalent vaccine, the vaccine strain selection committee in a meeting held on 20 - 24 February noted that there is evidence of increasing antigenic and genetic drift in circulating influenza A(H3N2) recently and that the proportion of type B viruses that are from the Yamagata lineage of type B has been increasing relative to the Victoria lineage. The committee therefore recommended a change in the composition of the next northern hemisphere vaccine formulation to include an A/Victoria/361/2011 (H3N2)-like virus and a B/Wisconsin/1/2010-like virus of the Yamagata lineage, and continuing the inclusion of an A/California/7/2009 (H1N1)pdm09-like virus."