For their guidance and support, the authors extend their thanks to Monique Berlier and Jean-Marie Preaud at PATH, France and to Marie-Pierre Preziosi and Michel Akt inhibitor Zaffran at WHO, Geneva. “
“Influenza is a major public health threat, and in the US, seasonal influenza epidemics account for more than 200,000 hospitalizations and more than 30,000 deaths annually [1] and [2]. Although influenza B is less of a public health burden than influenza A/H3N2 [2], influenza B viruses cause seasonal epidemics in adults every two to four years [3], and based on data across four seasons, clinical symptoms and hospital admission rates were similar in patients infected with
influenza B compared with influenza A [4]. Two antigenically-distinct influenza B lineages (B/Victoria and B/Yamagata) emerged in the 1980s, and have co-circulated in the US since 2000. However, seasonal influenza vaccines have conventionally been trivalent, including only one B lineage, meaning that mismatch between the circulating influenza
B virus and the vaccine strain is common. For example, between 2000 and 2010 in the US, the trivalent vaccine was mismatched for the circulating influenza B strain in six of ten seasons [5], resulting in reduced vaccine effectiveness in the mismatched years [6] and [7]. The huge impact of seasonal influenza vaccine mismatch with the circulating B lineage FRAX597 mouse was demonstrated in Taiwan during the 2011–2012 season when the trivalent vaccine contained a B/Victoria lineage strain whereas the predominant virus was an influenza B/Yamagata strain; based on laboratory-confirmed cases of influenza in vaccinated outpatients
identified over 6 months during the peak season, a test-negative case-control analysis showed that the adjusted vaccine effectiveness against influenza A was 54% (95% confidence interval: 3, 78), yet against influenza B was −66% (95% confidence interval: −132, −18) [8]. The inclusion of an influenza B strain from both the Victoria and Yamagata lineages in a quadrivalent vaccine could improve protection against influenza B, and could reduce the burden of Resminostat seasonal influenza illness, hospitalization, and death [9]. As such, for the first time, the World Health Organization (WHO) recommended B strains from both lineages for use in vaccines for the 2012–2013 season in the Northern Hemisphere [10]. There are currently four quadrivalent vaccines approved in the US, produced by three manufacturers (MedImmune, Sanofi Pasteur, GlaxoSmithKline Vaccines) [11]. A live attenuated quadrivalent vaccine has been assessed in children aged 2–17 years [12], and in adults aged 18–49 years [13], and in each study was found to provide non-inferior immune responses compared with a live attenuated trivalent influenza vaccine.