Announcement

**Giuseppe** · October 10, 2012, 11:10 AM

Re: ECDC: Influenza virus characterisation: Summary Europe, September 2012

From full PDF document: http://www.ecdc.europa.eu/en/publica...ember-2012.pdf

Influenza A(H3N2) virus analyses

As described before, A(H3N2) viruses have continued to be difficult to characterise antigenically by HI assay due to variable agglutination of red blood cells from guinea pigs, turkeys and humans.

Approximately 70% of viruses gave sufficient titre in HA assays, in the presence of 20nM oseltamivir, to be analysed by HI assay using guinea pig red blood cells in the presence of 20nM oseltamivir, added to circumvent the NA-mediated binding of H3N2 viruses to the red blood cells (Lin et al. 2010).

The results of HI assays carried out since the July report are shown in Table 3. HI assays using post-infection ferret antiserum raised against the virus recommended for the 2011/2012 northern hemisphere influenza vaccine, A/Perth/16/2009, showed all 35 test viruses to have ≥8-fold reductions in HI titre compared with the titre for the homologous virus.

Using post-infection ferret antiserum raised against the newly recommended, egg-propagated vaccine virus for the northern hemisphere 2012/2013 influenza season, A/Victoria/361/2011, only 8/35 test viruses gave an HI titre within fourfold of that of the homologous virus.

In contrast, with antiserum raised against the cell-culture propagated A/Victoria/361/2011 only 1/35 test viruses showed ≥8-fold reduced reactivity compared with the titre of the homologous cell-propagated virus (Table 3).

The test viruses also showed good reactivity with post-infection ferret antisera raised against other reference viruses propagated exclusively in cell culture, regardless of HA genetic group: A/Alabama/5/2010 (group 5), A/Stockholm/18/2011 (subgroup 3A), A/Athens/GR112/2012 (subgroup 3B), A/Hong Kong/3969/2011 (subgroup 3C) and A/Berlin/93/2011 (subgroup 3C).

However, test viruses reacted poorly with post-infection ferret antisera raised against other egg-propagated reference viruses, A/Victoria/208/2009 and A/Iowa/19/2010, compared to the HI reactivity of the homologous egg-propagated viruses.

The low reactivity of test viruses with antisera raised against each of the egg-adapted viruses, importantly including the new vaccine virus A/Victoria/361/2011, suggests that egg adaptation of the H3N2 reference viruses influences the immune response of the ferret and consequently the HI assay.

In light of these observations, results of HI tests and other serological assays with currently circulating A(H3N2) viruses continue to warrant careful consideration.

Phylogenetic analysis of the HA gene sequences of representative viruses has been carried out (Figure 2).

Viruses from the EU/EEA collected since January have HA genes that fall into HA genetic groups 5 and 6, and subgroups 3A, 3B and 3C.

The amino acid substitutions that are associated with each of these groupings are:

? Subgroup 3A: V223I ,N144D (resulting in the loss of a glycosylation site), and N145S, e.g. A/Stockholm/18/2011;
? Subgroup 3B: V223I, N145S, A198S and N312S, e.g. A/Athens/GR112/2012;
? Subgroup 3C: V223I, S45N, T48I, A198S and N312S, e.g. A/Hong Kong/3969/2011 and the prototype vaccine virus A/Victoria/361/2011, with some viruses also carrying the substitutions Q33R and N278K;
? Group 5: D53N, Y94H, I230V and E280A, e.g. A/Alabama/5/2010;
? Group 6: D53N, Y94H, S199A, I230V and E280A, e.g. A/Iowa/19/2010.

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**Giuseppe** · October 10, 2012, 11:16 AM

Re: ECDC: Influenza virus characterisation: Summary Europe, September 2012

From full PDF document: http://www.ecdc.europa.eu/en/publica...ember-2012.pdf

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Influenza A(H3N2)v virus

On 3 August 2012, the United States CDC issued a Health Advisory describing an increase in the number of influenza A(H3N2)v infections in three US states; CDC prepared further background information and provided regular updates.

Antigenic and genetic characterisation of H3N2v viruses has been described by Lindstrom et al., 2012.

The virus was characterised as being antigenically distinct from currently circulating human seasonal influenza viruses and to be a reassortant virus with seven genes from swine influenza 'triple reassortant' H3N2 viruses and the M gene from an influenza A(H1N1)pdm09 virus

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The prevalence of antibodies in human sera cross-reactive with H3N2v virus has been examined in Norway, the USA and Canada, and the authors concluded that there was a high level of immunity in young adults but less so in other groups.

Active surveillance of swine influenza has shown that influenza A(H3N2)v viruses have not circulated in pigs in Europe.

Antigenic analysis of two H3N2v viruses, three viruses from humans infected with triple reassortant swine influenza viruses (TRV) and two human seasonal H3N2 viruses, performed at the WHO CC in London (Table 6), support the conclusion that both triple reassortant H3N2 and H3N2v influenza viruses are antigenically distinct from recent human seasonal influenza viruses.

Risk assessments for these A(H3N2)v viruses as a risk to public health have been posted by the United States CDC and ECDC.

A description of results generated by the WHO Collaborating Centre for Reference and Research on Influenza, based at the MRC National Institute for Medical Research in London, and evaluated at the WHO Vaccine

Composition Meetings held at WHO Geneva from 20 to 22 February 2012 and Beijing, China, from 17 to 19 September 2012 can be found at:

http://www.nimr.mrc.ac.uk/documents/about/interim-report-feb-2012.pdf

http://www.nimr.mrc.ac.uk/documents/about/Interim_Report_September_2012_2.pdf

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Announcement

ECDC: Influenza virus characterisation: Summary Europe, September 2012

ECDC: Influenza virus characterisation: Summary Europe, September 2012

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