Influenza vaccine effectiveness in Italy: Age, subtype-specific and vaccine type estimates 2014/15 season

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Vaccine. 2016 May 4. pii: S0264-410X(16)30237-7. doi: 10.1016/j.vaccine.2016.04.072. [Epub ahead of print]
Influenza vaccine effectiveness in Italy: Age, subtype-specific and vaccine type estimates 2014/15 season.

Rizzo C¹, Bella A², Alfonsi A², Puzelli S², Palmieri AP², Chironna M³, Pariani E⁴, Piatti A⁵, Tiberti D⁶, Ghisetti V⁷, Rangoni R⁸, Colucci ME⁹, Affanni P⁹, Germinario C³, Castrucci MR².
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Abstract

The 2014/15 influenza season in Europe was characterised by the circulation of influenza A(H3N2) viruses with an antigenic and genetic mismatch from the vaccine strain A/Texas/50/2012(H3N2) recommended for the Northern hemisphere for the 2014/15 season. Italy, differently from other EU countries where most of the subtyped influenza A viruses were H3N2, experienced a 2014/15 season characterized by an extended circulation of two influenza viruses: A(H1N1)pdm09 and A(H3N2), that both contributed substantially to morbidity. Within the context of the existing National sentinel influenza surveillance system (InfluNet) a test-negative case-control study was established in order to produce vaccine effectiveness (VE) estimates. The point estimates VE were adjusted by age group (<5; 5-15; 15-64; 65+ years), the presence of at least one chronic condition, target group for vaccination and need help for walking or bathing. In Italy, adjusted estimates of the 2014/15 seasonal influenza VE against medically attended influenza-like illness (ILI) laboratory-confirmed as influenza for all age groups were 6.0% (95%CI: -36.5 to 35.2%), 43.6% (95%CI: -3.7 to 69.3%), -84.5% (95%CI: (-190.4 to -17.2%) and 50.7% (95% CI: -2.5 to 76.3%) against any influenza virus, A(H1N1)pdm09, A(H3N2) and B, respectively. These results suggest evidence of good VE against A(H1N1)pdm09 and B viruses in Italy and evidence of lack of VE against A(H3N2) virus due to antigenic and genetic mismatch between circulating A(H3N2) and the respective 2014/15 vaccine strain.
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KEYWORDS:

Influenza; Test negative case?control studies; Vaccine effectiveness

PMID: 27154392 [PubMed - as supplied by publisher] .