Early influenza vaccine effectiveness results 2015-16: I-MOVE multicentre case-control study

• Published in: Euro surveillance : bulletin européen sur les maladies transmissibles 2016-02, Vol.21 (6), p.1
• Main Authors: Kissling, E, Valenciano, M
• Format: Article
• Language: English
• Subjects: Case-Control Studies; Confidence intervals; Effectiveness; Epidemiological Monitoring; Humans; Influenza; Influenza A Virus, H1N1 Subtype; Influenza Vaccines - administration & dosage; Influenza Vaccines - immunology; Influenza, Human - epidemiology; Influenza, Human - prevention & control; Sample size; Treatment Outcome; Vaccines
• ISSN: 1560-7917; 1025-496X; 1560-7917
• DOI: 10.2807/1560-7917.ES.2016.21.6.30134

On 11 February 2016, the Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) published the 2015-16 interim vaccine effectiveness (VE) estimates against influenza from a multi-centre case control study in 10 study sites: Germany, France, Hungary, Ireland, Italy, Poland, Portugal, Spain, Sweden and the Netherlands, on their website. Adjusted VE interim results against any influenza among all ages were at 46.3% (95% confidence interval (CI): 4.9-69.7%) and 45.2% (95% CI: -12.5-73.3%) among the 18-64 year olds. Among those aged 65 years and older, there were only 14 influenza cases in the study. The adjusted VE against influenza A(H1N1)pdm09 was at 44.2% (95% CI: -3.1-69.8%) among all ages and thus lower compared with end of season estimates published in previous years (55.5% in 2010-11, 50.4% in 2012-13; 47.5% in 2013-14, 54.2% in 2014-15). Early season influenza VE was measured against medically-attended laboratory-confirmed influenza from week 41/2015 to week 3/2016 using a test-negative design as described in the I-MOVE generic protocol and in the I-MOVE multicentre case-control publications. Some 1,933 influenza-like illness patients among whom 348 were positive to influenza were included: four cases of influenza A not subtyped, 246 A(H1N1)pdm09, 21 A(H3N2), and 77 influenza B cases. Among the 37 influenza B cases where lineage was available, 36 (97.3%) were of the Victoria lineage, a lineage not included in the trivalent vaccine. For this interim analysis, there was no information on genetic characterisation of the viruses. The recently published European Centre for Disease Prevention and Control risk assessment reported that all A(H1N1)pdm09 viruses characterised in the European Union up to week three belonged to the 6B subgroup. The interim estimates should be interpreted with caution. The 2015-16 season started late in the participating countries and the sample size for these interim estimates is low, resulting in low precision. The final estimates will be available at the end of the influenza season.