Circulating influenza viruses and the effectiveness of seasonal influenza vaccine in Romania, season 2012-2013 / Virusurile gripale circulante și eficacitatea vaccinului gripal sezonier în România, în sezonul 2012-2013

Backgound. Using influenza epidemiological and virological surveillance data, we aimed at investigating the profile of influenza viruses circulating in Romania during the season 2012-2013 and estimating the effectiveness (VE) of the seasonal vaccine. Methods. We tested all specimens collected from patients with influenza like illness (ILI) in the national surveillance system between week 40/2012 to week 20/2013. Influenza A/B positive specimens identified by molecular detection (RT-PCR) were further characterized. We used hemagglutination inhibition assay for antigenic characterization and chemiluminiscence assay for the antiviral susceptibility testing. Subsequently we conducted nucleotide sequencing of hemagglutinin and neuraminidase genes and phylogenetic tree analyses. We estimated influenza VE using the test negative case-control study design, as 1-odds ratio of vaccination among ILI cases positive for influenza and ILI negative controls. Results and Discussions. We tested 1087 specimens, and 537 cases were positive (56.2% influenza B, 40.6% A(H1N1)pdm09, 3.2% A(H3N2). Sixty-four influenza viruses were antigenically and/or genetically characterized. A(H1N1)pdm09 viruses were related to the vaccine strain A/ California/07/2009 and clustered with genetic group 6 similar to A/St. Petersburg/27/2011. Influenza B viruses belonged to clade 2 of type B/Yamagata lineage, related to B/Estonia/55669/2011 except one, B/Victoria lineage, representative strain B/Brisbane/60/2008. A(H3) viruses clustered with group 3C of the A/Victoria/208/2009 clade, similar to the vaccine strain A/Victoria/361/2011. All tested strains (57) demonstrated susceptibility to oseltamivir and zanamivir. The adjusted seasonal influenza vaccine effectiveness against influenza A(H1N1)pdm09 (N=119) was 76.9% (95% CI: -113.4, 98.5), suggesting a good protection, consistent with the good match between the vaccine and circulating strains.