WHO announcement of strains to be included in the Southern Hemisphere 2013 influenza vaccine compositionArchived

The World Health Organization (WHO)–September 2012

Following a meeting of the global influenza collaborating centres in Beijing hosted by the newest Centre that in China the World Health Organization (WHO) recently recommended that influenza vaccines to be used in the 2013 Southern Hemisphere (SH) influenza season should contain the same three strains as the vaccines that now are being used in the Northern Hemisphere (NH). The recommendation has been published in WHO’s website. Two of the strains included in this new strain selection will be different from those that were used in the SH vaccines this year 2012 (summertime in Europe). The recommendation that WHO issued in February 2012 for vaccine composition of the vaccine to be used in the NH this Autumn already included a change in the influenza A(H3N2) and B strains. These recommendations for the SH influenza vaccine composition are made in September or October to allow sufficient time for vaccine preparation and mass production, process which typically takes several months to complete.

Hence in relation to the virological composition, WHO has recommended including the following strains in the vaccine to be used in the 2013 SH influenza season:

• A/California/7/2009 (H1N1)pdm09 (which is the ‘2009 pandemic’ virus)
• A/Victoria/361/2011 (H3N2)
• B/Wisconsin/1/2010 (Yamagata lineage)

The recommendation is accompanied by a review of the influenza activity in the world from February to September 2012. This review describes how all seasonal A(H1N1) influenza viruses were the ‘2009 pandemic’ strain i.e. the A(H1N1)pdm09 influenza virus, which is included in the vaccine currently in use in the NH. The A(H1N1)pdm09 virus has been included in every WHO influenza vaccine recommendation since September 2009, when it was first included in the vaccine composition of the vaccine to be used in the SH 2010 influenza season. Most of the A(H3N2) influenza viruses circulating in the SH in 2012 were closely related to A/Victoria/361/2011, the strain in the 2012-2013 vaccine. With regards to influenza B, viruses from both Victoria and Yamagata lineages circulated widely in 2012, but the B/Wisconsin/1/2010 strain that has been recommended for inclusion in the 2012-2013 vaccine is of the Yamagata lineage. For pharmaceutical companies making a quadrivalent (four-strain) vaccine with two B strains, the WHO recommends including a B/Brisbane/60/2008-like virus, which is of the Victoria lineage and was used in the 2012 SH vaccines.

On antiviral resistance, the data presented in WHO’s report suggested that only 1.4% (16 of 1,124) of A(H1N1)pdm09 viruses that were tested were resistant to oseltamivir, but most of the resistant isolates were not associated with use of the antiviral. All of these isolates remained susceptible to zanamivir. In addition, only one A(H3N2) isolate and one type B isolate were found to show reduced susceptibility to neuraminidase inhibitors.

ECDC Comment (7 October 2012):

The switch to a new A(H3N2) influenza virus component in the vaccine is important as there have been strong indications of lowered field effectiveness of the flu vaccines in the Northern Hemisphere season just passed for the main risk groups .(1-3) I.e. the virology has matched the findings in the field.

A version of the description mentioned above for virological isolates coming from the EU/EEA European countries was published by ECDC having been prepared by the Community Network Reference Laboratory (specifically the WHO Influenza Collaborating Centre in London).(4) This noted two important developments. Firstly recent B/Yamagata-lineage viruses fell into two genetic clades, represented by the recommended vaccine component for the 2012/2013 influenza season, B/Wisconsin/1/2010 (clade 3) and B/Estonia/55669/2012 (clade 2). The viruses in these clades are antigenically distinguishable. This suggests that the B/Wisconsin/1/2010 Yamagata component may not be that effective against all the B Yamagata strains that may circulate in Europe in season 2012-2013. Also there remains some concerns over the new A(H3N2) vaccines in that viruses isolated in mammalian cells show low titres with post-infection ferret antisera raised against egg-propagated viruses, including the new vaccine virus A/Victoria/361/2011 for A(H3N2) viruses. This did not apply for current reference viruses propagated exclusively in tissue culture. Therefore, in the laboratories, it is crucial to use the correct controls in the antigenic characterisation analyses.Both findigs indicate the importance of looking at field effectiveness this coming season to see if the improvement in antigenic composition of the seasonal vaccine is reflected in increased field effectiveness.