The 2013/14 influenza season to date in Canada has been characterised by predominant (90%) A(H1N1)pdm09 activity. Vaccine effectiveness (VE) was assessed in January 2014 by Canada's sentinel surveillance network using a test-negative case-control design. Interim adjusted-VE against medically-attended laboratory-confirmed influenza A(H1N1)pdm09 infection was 74% (95% CI: 58-83). Relative to vaccine, A(H1N1)pdm09 viruses were antigenically similar and genetically well conserved, with most showing just three mutations across the 50 amino acids comprising antigenic sites of the haemagglutinin protein.
Skowronski, D. M., Chambers, C., Sabaiduc, S., De Serres, G., Dickinson, J. A., Winter, A. L., … Li, Y. (2014). Interim estimates of 2013/14 vaccine effectiveness against influenza A(H1N1)PDM09 from Canada’s sentinel surveillance network, January 2014. Eurosurveillance, 19(5). https://doi.org/10.2807/1560-7917.ES2014.19.5.20690