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Annual influenza vaccine effectiveness meeting 2013 – summary of discussions on obtained results and recommended future research focus

13 Sep 2013
Influenza vaccine experts from thirteen EU countries and invited guests from Canada and the US gathered for three days July 1-3, 2013 in Annecy, France to report and discuss obtained national and pooled multi-country seasonal influenza vaccine effectiveness (VE) obtained in the 2012/2013 season. The meeting was co-organised by ECDC and Epiconcept.
Presentations included results from the mid-season analysis, preliminary results from the end-of-season analysis and future visions for continued research.
Interim results published in January-February 2013 from Europe, Canada, and the US were first compared and discussed (see table below). Vaccine effectiveness varied somewhat by influenza subtype but given that slightly different methodology for collection of data was utilized in the different geographical regions, results were surprisingly similar.
  Influenza type/ Geographical region 
VE (%)
VE (%)
United States
VE (%)

 All influenza 
50%  (95%CI-21-80%)
52% (95%CI 25-69%) 
 62% (95%CI 51-71%)
 All influenza A
  55% (95%CI 39-67%)
 Influenza A H1N1pdm09
62% (95%CI -22-88%) 
 Influenza A H3N2
42% (95%CI -67-80%)
45% (95%CI 13-66%)
 All Influenza B
78% (95%CI 18-94%)
 70% (95%CI 56-80%)
*Not enough influenza A H1N1pdm09, influenza A H3N2 and influenza B subtypes in circulation in some of the geographical regions at the time to calculate estimates for these vaccine components
The influenza B component of the trivalent combination vaccines used this season induced the best protection (VE>70%) (1, 3), and the lowest effectiveness was observed for the subtype influenza A H3N2 [1, 2].
The reasons for the low effectiveness reported both in Europe and North America for the influenza A H3N2 component, is likely due to what WHO recently reported, namely that this season the match between the influenza A H3N2 vaccine strain and the influenza A H3N2 strains circulating in the Northern hemisphere populations was suboptimal.  A virus evolution had occurred during production of vaccine virus in eggs without a similar evolution in the viruses circulating in the human population [4].
The interim results from Europe and North America were  presented to the 2013 WHO influenza strain selection meeting and contributed to the selection of the viruses to be included in the vaccines for the Northern hemisphere for the upcoming 2013/2014 season [4]. 
Further, the preliminary end-of-season VE results from Europe and North America were discussed and final data are expected to be published in the near future. They will include age-specific and risk-group specific VE data. 
Representatives from the public health and regulatory sectors participating in the meeting welcomed the results and encouraged continued work in view of the 2009 EU Council recommendation on seasonal influenza immunization (offer seasonal influenza vaccine to >75% of elderly and risk groups in all EU Member States) [5] and the new 2012 pharmacovigilance legislation mentioning vaccine efficacy to be analysed [6]. 
Assessing vaccine effectiveness in the EU is of particular interest to public health responsible for the organized immunization programmes with many different variants of influenza vaccines authorised and available for use; inactivated whole virion influenza vaccines, inactivated split influenza vaccines, inactivated subunit influenza vaccines, inactivated virosomal influenza vaccines and live attenuated influenza vaccines with limited knowledge on their individual impact [7].
At the end of the meeting recommended future research areas were discussed. It was agreed that the following areas beyond the yearly effectiveness analysis need to be addressed in future studies; a) serological correlates of protection following infection and vaccination, b) waning immunity following vaccination in the first and subsequent seasons,  c) influence of previous vaccination/infection on obtained immune response after vaccination and d) genetic characterization of influenza viruses causing breakthrough infections in vaccinated individuals.
Of relevance to the future research are also the new quadrivalent seasonal influenza vaccines already available for use in the US for the 2013/2014 season and under assessment in the EU (8-12). Long-term, there are great hopes for the development of universal influenza vaccines able to protect against all types/subtypes of influenza. EU DG RTD has just awarded five research projects funding for development of universal influenza vaccines [13]. The established vaccine effectiveness assessment methodology in the EU will likely prove valuable assessing the many new foreseen developments.
Comments or questions on this Public Health Development are welcome and should be addressed to:
1. Valenciano M, Kissling E; I-MOVE Case-Control Study Team. Early estimates of seasonal influenza vaccine effectiveness in Europe: results from the I-MOVE multicentre case-control study, 2012/13. Euro Surveill. 2013 Feb 14;18(7):3.
2. Skowronski DM, Janjua NZ, De Serres G, Dickinson JA, Winter AL, Mahmud SM, Sabaiduc S, Gubbay JB, Charest H, Petric M, Fonseca K, Van Caeseele P, Kwindt TL, Krajden M, Eshaghi A, Li Y. Interim estimates of influenza vaccine effectiveness in 2012/13 from Canada's sentinel surveillance network, January 2013. Euro Surveill. 2013 Jan 31;18(5). pii: 20394.
3. Early estimates of seasonal influenza vaccine effectiveness--United States, January 2013. MMWR Morb Mortal Wkly Rep. 2013 Jan 18;62(2):32-5.
Public Health Development prepared by Kari Johansen and Andrew Amato-Gauci
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